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  • GWB | 30 Posts in 60 Days Update

    - by Staff of Geeks
    One month after the contest started, we definitely have some leaders and one blogger who has reached the mark.  Keep up the good work guys, I have really enjoyed the content being produced by our bloggers. Current Winners: Enrique Lima (37 posts) - http://geekswithblogs.net/enriquelima Almost There: Stuart Brierley (28 posts) - http://geekswithblogs.net/StuartBrierley Dave Campbell (26 posts) - http://geekswithblogs.net/WynApseTechnicalMusings Eric Nelson (23 posts) - http://geekswithblogs.net/iupdateable Coming Along: Liam McLennan (17 posts) - http://geekswithblogs.net/liammclennan Christopher House (13 posts) - http://geekswithblogs.net/13DaysaWeek mbcrump (13 posts) - http://geekswithblogs.net/mbcrump Steve Michelotti (10 posts) - http://geekswithblogs.net/michelotti Michael Freidgeim (9 posts) - http://geekswithblogs.net/mnf MarkPearl (9 posts) - http://geekswithblogs.net/MarkPearl Brian Schroer (8 posts) - http://geekswithblogs.net/brians Chris Williams (8 posts) - http://geekswithblogs.net/cwilliams CatherineRussell (7 posts) - http://geekswithblogs.net/CatherineRussell Shawn Cicoria (7 posts) - http://geekswithblogs.net/cicorias Matt Christian (7 posts) - http://geekswithblogs.net/CodeBlog James Michael Hare (7 posts) - http://geekswithblogs.net/BlackRabbitCoder John Blumenauer (7 posts) - http://geekswithblogs.net/jblumenauer Scott Dorman (7 posts) - http://geekswithblogs.net/sdorman   Technorati Tags: Standings,Geekswithblogs,30 in 60

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  • 30 in 60 Contest | Standings Update

    - by Staff of Geeks
    The contest has definitely ended the first week with a clear leader.  One of our new bloggers, Enrique Lima, has posted 20 times since the beginning of the contest with some great content on Team Foundation Server.  Another noticeable face we see on the leader board is Chris Williams who is making headway.  Chris, are you going to challenge up D’Arcy Lussier for the lead position on GWB again, notice who isn’t on this list :D.  Also, Chris House who is a new blogger is making some strong strides.  And finally, let us not forget Dave Campbell who writes Silverlight Cream who always has great content for us.  We hope to see more names joining this list soon, what else could be better than a world full of Geekswithblogs.net custom shirts?   Current Leader Board: Enrique Lima (20 posts) - http://geekswithblogs.net/enriquelima Eric Nelson (7 posts) - http://geekswithblogs.net/iupdateable Christopher House (7 posts) - http://geekswithblogs.net/13DaysaWeek StuartBrierley (7 posts) - http://geekswithblogs.net/StuartBrierley Dave Campbell (6 posts) - http://geekswithblogs.net/WynApseTechnicalMusings Chris Williams (5 posts) - http://geekswithblogs.net/cwilliams Frez (4 posts) - http://geekswithblogs.net/Frez MarkPearl (4 posts) - http://geekswithblogs.net/MarkPearl mbcrump (4 posts) - http://geekswithblogs.net/mbcrump Rajesh Charagandla (3 posts) - http://geekswithblogs.net/crajesh Technorati Tags: 30 in 60,Geekswithblogs,Standings

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  • Computer Networks UNISA - Chap 12 – Networking Security

    - by MarkPearl
    After reading this section you should be able to Identify security risks in LANs and WANs and design security policies that minimize risks Explain how physical security contributes to network security Discuss hardware and design based security techniques Understand methods of encryption such as SSL and IPSec, that can secure data in storage and in transit Describe how popular authentication protocols such as RADIUS< TACACS,Kerberos, PAP, CHAP, and MS-CHAP function Use network operating system techniques to provide basic security Understand wireless security protocols such as WEP, WPA and 802.11i Security Audits Before spending time and money on network security, examine your networks security risks – rate and prioritize risks. Different organizations have different levels of network security requirements. Security Risks Not all security breaches result from a manipulation of network technology – there are human factors that can play a role as well. The following categories are areas of considerations… Risks associated with People Risks associated with Transmission and Hardware Risks associated with Protocols and Software Risks associated with Internet Access An effective security policy A security policy identifies your security goals, risks, levels of authority, designated security coordinator and team members, responsibilities for each team member, and responsibilities for each employee. In addition it specifies how to address security breaches. It should not state exactly which hardware, software, architecture, or protocols will be used to ensure security, nor how hardware or software will be installed and configured. A security policy must address an organizations specific risks. to understand your risks, you should conduct a security audit that identifies vulnerabilities and rates both the severity of each threat and its likelihood of occurring. Security Policy Content Security policy content should… Policies for each category of security Explain to users what they can and cannot do and how these measures protect the networks security Should define what confidential means to the organization Response Policy A security policy should provide for a planned response in the event of a security breach. The response policy should identify the members of a response team, all of whom should clearly understand the the security policy, risks, and measures in place. Some of the roles concerned could include… Dispatcher – the person on call who first notices the breach Manager – the person who coordinates the resources necessary to solve the problem Technical Support Specialist – the person who focuses on solving the problem Public relations specialist – the person who acts as the official spokesperson for the organization Physical Security An important element in network security is restricting physical access to its components. There are various techniques for this including locking doors, security people at access points etc. You should identify the following… Which rooms contain critical systems or data and must be secured Through what means might intruders gain access to these rooms How and to what extent are authorized personnel granted access to these rooms Are authentication methods such as ID cards easy to forge etc. Security in Network Design The optimal way to prevent external security breaches from affecting you LAN is not to connect your LAN to the outside world at all. The next best protection is to restrict access at every point where your LAN connects to the rest of the world. Router Access List – can be used to filter or decline access to a portion of a network for certain devices. Intrusion Detection and Prevention While denying someone access to a section of the network is good, it is better to be able to detect when an attempt has been made and notify security personnel. This can be done using IDS (intrusion detection system) software. One drawback of IDS software is it can detect false positives – i.e. an authorized person who has forgotten his password attempts to logon. Firewalls A firewall is a specialized device, or a computer installed with specialized software, that selectively filters or blocks traffic between networks. A firewall typically involves a combination of hardware and software and may reside between two interconnected private networks. The simplest form of a firewall is a packet filtering firewall, which is a router that examines the header of every packet of data it receives to determine whether that type of packet is authorized to continue to its destination or not. Firewalls can block traffic in and out of a LAN. NOS (Network Operating System) Security Regardless of the operating system, generally every network administrator can implement basic security by restricting what users are authorized to do on a network. Some of the restrictions include things related to Logons – place, time of day, total time logged in, etc Passwords – length, characters used, etc Encryption Encryption is the use of an algorithm to scramble data into a format that can be read only by reversing the algorithm. The purpose of encryption is to keep information private. Many forms of encryption exist and new ways of cracking encryption are continually being invented. The following are some categories of encryption… Key Encryption PGP (Pretty Good Privacy) SSL (Secure Sockets Layer) SSH (Secure Shell) SCP (Secure CoPy) SFTP (Secure File Transfer Protocol) IPSec (Internet Protocol Security) For a detailed explanation on each section refer to pages 596 to 604 of textbook Authentication Protocols Authentication protocols are the rules that computers follow to accomplish authentication. Several types exist and the following are some of the common authentication protocols… RADIUS and TACACS PAP (Password Authentication Protocol) CHAP and MS-CHAP EAP (Extensible Authentication Protocol) 802.1x (EAPoL) Kerberos Wireless Network Security Wireless transmissions are particularly susceptible to eavesdropping. The following are two wireless network security protocols WEP WPA

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  • Sorting Algorithms

    - by MarkPearl
    General Every time I go back to university I find myself wading through sorting algorithms and their implementation in C++. Up to now I haven’t really appreciated their true value. However as I discovered this last week with Dictionaries in C# – having a knowledge of some basic programming principles can greatly improve the performance of a system and make one think twice about how to tackle a problem. I’m going to cover briefly in this post the following: Selection Sort Insertion Sort Shellsort Quicksort Mergesort Heapsort (not complete) Selection Sort Array based selection sort is a simple approach to sorting an unsorted array. Simply put, it repeats two basic steps to achieve a sorted collection. It starts with a collection of data and repeatedly parses it, each time sorting out one element and reducing the size of the next iteration of parsed data by one. So the first iteration would go something like this… Go through the entire array of data and find the lowest value Place the value at the front of the array The second iteration would go something like this… Go through the array from position two (position one has already been sorted with the smallest value) and find the next lowest value in the array. Place the value at the second position in the array This process would be completed until the entire array had been sorted. A positive about selection sort is that it does not make many item movements. In fact, in a worst case scenario every items is only moved once. Selection sort is however a comparison intensive sort. If you had 10 items in a collection, just to parse the collection you would have 10+9+8+7+6+5+4+3+2=54 comparisons to sort regardless of how sorted the collection was to start with. If you think about it, if you applied selection sort to a collection already sorted, you would still perform relatively the same number of iterations as if it was not sorted at all. Many of the following algorithms try and reduce the number of comparisons if the list is already sorted – leaving one with a best case and worst case scenario for comparisons. Likewise different approaches have different levels of item movement. Depending on what is more expensive, one may give priority to one approach compared to another based on what is more expensive, a comparison or a item move. Insertion Sort Insertion sort tries to reduce the number of key comparisons it performs compared to selection sort by not “doing anything” if things are sorted. Assume you had an collection of numbers in the following order… 10 18 25 30 23 17 45 35 There are 8 elements in the list. If we were to start at the front of the list – 10 18 25 & 30 are already sorted. Element 5 (23) however is smaller than element 4 (30) and so needs to be repositioned. We do this by copying the value at element 5 to a temporary holder, and then begin shifting the elements before it up one. So… Element 5 would be copied to a temporary holder 10 18 25 30 23 17 45 35 – T 23 Element 4 would shift to Element 5 10 18 25 30 30 17 45 35 – T 23 Element 3 would shift to Element 4 10 18 25 25 30 17 45 35 – T 23 Element 2 (18) is smaller than the temporary holder so we put the temporary holder value into Element 3. 10 18 23 25 30 17 45 35 – T 23   We now have a sorted list up to element 6. And so we would repeat the same process by moving element 6 to a temporary value and then shifting everything up by one from element 2 to element 5. As you can see, one major setback for this technique is the shifting values up one – this is because up to now we have been considering the collection to be an array. If however the collection was a linked list, we would not need to shift values up, but merely remove the link from the unsorted value and “reinsert” it in a sorted position. Which would reduce the number of transactions performed on the collection. So.. Insertion sort seems to perform better than selection sort – however an implementation is slightly more complicated. This is typical with most sorting algorithms – generally, greater performance leads to greater complexity. Also, insertion sort performs better if a collection of data is already sorted. If for instance you were handed a sorted collection of size n, then only n number of comparisons would need to be performed to verify that it is sorted. It’s important to note that insertion sort (array based) performs a number item moves – every time an item is “out of place” several items before it get shifted up. Shellsort – Diminishing Increment Sort So up to now we have covered Selection Sort & Insertion Sort. Selection Sort makes many comparisons and insertion sort (with an array) has the potential of making many item movements. Shellsort is an approach that takes the normal insertion sort and tries to reduce the number of item movements. In Shellsort, elements in a collection are viewed as sub-collections of a particular size. Each sub-collection is sorted so that the elements that are far apart move closer to their final position. Suppose we had a collection of 15 elements… 10 20 15 45 36 48 7 60 18 50 2 19 43 30 55 First we may view the collection as 7 sub-collections and sort each sublist, lets say at intervals of 7 10 60 55 – 20 18 – 15 50 – 45 2 – 36 19 – 48 43 – 7 30 10 55 60 – 18 20 – 15 50 – 2 45 – 19 36 – 43 48 – 7 30 (Sorted) We then sort each sublist at a smaller inter – lets say 4 10 55 60 18 – 20 15 50 2 – 45 19 36 43 – 48 7 30 10 18 55 60 – 2 15 20 50 – 19 36 43 45 – 7 30 48 (Sorted) We then sort elements at a distance of 1 (i.e. we apply a normal insertion sort) 10 18 55 60 2 15 20 50 19 36 43 45 7 30 48 2 7 10 15 18 19 20 30 36 43 45 48 50 55 (Sorted) The important thing with shellsort is deciding on the increment sequence of each sub-collection. From what I can tell, there isn’t any definitive method and depending on the order of your elements, different increment sequences may perform better than others. There are however certain increment sequences that you may want to avoid. An even based increment sequence (e.g. 2 4 8 16 32 …) should typically be avoided because it does not allow for even elements to be compared with odd elements until the final sort phase – which in a way would negate many of the benefits of using sub-collections. The performance on the number of comparisons and item movements of Shellsort is hard to determine, however it is considered to be considerably better than the normal insertion sort. Quicksort Quicksort uses a divide and conquer approach to sort a collection of items. The collection is divided into two sub-collections – and the two sub-collections are sorted and combined into one list in such a way that the combined list is sorted. The algorithm is in general pseudo code below… Divide the collection into two sub-collections Quicksort the lower sub-collection Quicksort the upper sub-collection Combine the lower & upper sub-collection together As hinted at above, quicksort uses recursion in its implementation. The real trick with quicksort is to get the lower and upper sub-collections to be of equal size. The size of a sub-collection is determined by what value the pivot is. Once a pivot is determined, one would partition to sub-collections and then repeat the process on each sub collection until you reach the base case. With quicksort, the work is done when dividing the sub-collections into lower & upper collections. The actual combining of the lower & upper sub-collections at the end is relatively simple since every element in the lower sub-collection is smaller than the smallest element in the upper sub-collection. Mergesort With quicksort, the average-case complexity was O(nlog2n) however the worst case complexity was still O(N*N). Mergesort improves on quicksort by always having a complexity of O(nlog2n) regardless of the best or worst case. So how does it do this? Mergesort makes use of the divide and conquer approach to partition a collection into two sub-collections. It then sorts each sub-collection and combines the sorted sub-collections into one sorted collection. The general algorithm for mergesort is as follows… Divide the collection into two sub-collections Mergesort the first sub-collection Mergesort the second sub-collection Merge the first sub-collection and the second sub-collection As you can see.. it still pretty much looks like quicksort – so lets see where it differs… Firstly, mergesort differs from quicksort in how it partitions the sub-collections. Instead of having a pivot – merge sort partitions each sub-collection based on size so that the first and second sub-collection of relatively the same size. This dividing keeps getting repeated until the sub-collections are the size of a single element. If a sub-collection is one element in size – it is now sorted! So the trick is how do we put all these sub-collections together so that they maintain their sorted order. Sorted sub-collections are merged into a sorted collection by comparing the elements of the sub-collection and then adjusting the sorted collection. Lets have a look at a few examples… Assume 2 sub-collections with 1 element each 10 & 20 Compare the first element of the first sub-collection with the first element of the second sub-collection. Take the smallest of the two and place it as the first element in the sorted collection. In this scenario 10 is smaller than 20 so 10 is taken from sub-collection 1 leaving that sub-collection empty, which means by default the next smallest element is in sub-collection 2 (20). So the sorted collection would be 10 20 Lets assume 2 sub-collections with 2 elements each 10 20 & 15 19 So… again we would Compare 10 with 15 – 10 is the winner so we add it to our sorted collection (10) leaving us with 20 & 15 19 Compare 20 with 15 – 15 is the winner so we add it to our sorted collection (10 15) leaving us with 20 & 19 Compare 20 with 19 – 19 is the winner so we add it to our sorted collection (10 15 19) leaving us with 20 & _ 20 is by default the winner so our sorted collection is 10 15 19 20. Make sense? Heapsort (still needs to be completed) So by now I am tired of sorting algorithms and trying to remember why they were so important. I think every year I go through this stuff I wonder to myself why are we made to learn about selection sort and insertion sort if they are so bad – why didn’t we just skip to Mergesort & Quicksort. I guess the only explanation I have for this is that sometimes you learn things so that you can implement them in future – and other times you learn things so that you know it isn’t the best way of implementing things and that you don’t need to implement it in future. Anyhow… luckily this is going to be the last one of my sorts for today. The first step in heapsort is to convert a collection of data into a heap. After the data is converted into a heap, sorting begins… So what is the definition of a heap? If we have to convert a collection of data into a heap, how do we know when it is a heap and when it is not? The definition of a heap is as follows: A heap is a list in which each element contains a key, such that the key in the element at position k in the list is at least as large as the key in the element at position 2k +1 (if it exists) and 2k + 2 (if it exists). Does that make sense? At first glance I’m thinking what the heck??? But then after re-reading my notes I see that we are doing something different – up to now we have really looked at data as an array or sequential collection of data that we need to sort – a heap represents data in a slightly different way – although the data is stored in a sequential collection, for a sequential collection of data to be in a valid heap – it is “semi sorted”. Let me try and explain a bit further with an example… Example 1 of Potential Heap Data Assume we had a collection of numbers as follows 1[1] 2[2] 3[3] 4[4] 5[5] 6[6] For this to be a valid heap element with value of 1 at position [1] needs to be greater or equal to the element at position [3] (2k +1) and position [4] (2k +2). So in the above example, the collection of numbers is not in a valid heap. Example 2 of Potential Heap Data Lets look at another collection of numbers as follows 6[1] 5[2] 4[3] 3[4] 2[5] 1[6] Is this a valid heap? Well… element with the value 6 at position 1 must be greater or equal to the element at position [3] and position [4]. Is 6 > 4 and 6 > 3? Yes it is. Lets look at element 5 as position 2. It must be greater than the values at [4] & [5]. Is 5 > 3 and 5 > 2? Yes it is. If you continued to examine this second collection of data you would find that it is in a valid heap based on the definition of a heap.

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  • Cryptographic Validation Explained

    - by MarkPearl
    We have been using LogicNP’s CryptoLicensing for some of our software and I was battling to understand how exactly the whole process worked. I was sent the following document which really helped explain it – so if you ever use the same tool it is well worth a read. Licensing Basics LogicNP CryptoLicensing For .Net is the most advanced and state-of-the art licensing and copy protection system you can use for your software. LogicNP CryptoLicensing System uses the latest cryptographic technology to generate and validate licenses. The cryptographic algorithm used is the RSA algorithm which consists of a pair of keys called as the generation key and the validation key. Data encrypted using the generation key can only be decrypted using the corresponding validation key. How does cryptographic validation work? When a new license project is created, a unique validation-generation key pair is created for the project. When LogicNP CryptoLicensing For .Net generates licenses, it encrypts the license settings using the generation key. The validation key can be safely distributed with your software and is used during validation. During license validation, LogicNP CryptoLicensing For .Net attempts to decrypt the encrypted license code using the validation key. If the decryption is successful, this means that the data was encrypted using the generation key, since only the corresponding validation key can decrypt data encrypted with the generation key. This further means that not only is the license valid but that it was generated by you and only you since nobody else has access to the generation key. Generation Key This key is used by CryptoLicensing Generator to generate encrypted license codes. This key is stored in the license project file, so the license project file must be kept secure and confidential and must be accorded the same care as any other critical asset such as source code. Validation Key This key is used for validating generated license codes. It is the same key displayed in the 'Get Validation Key And Code' dialog (Ctrl+K) and is used by your software when validating license codes (using LogicNP.CryptoLicensing.dll). Unlike the generation key, it is not necessary to keep this key secure and confidential. Note that the generation key pair is stored in the project file created by LogicNP CryptoLicensing For .Net, so it is very important to backup this file and to keep it secure. Once the file is lost, it is not possible to retrieve the key pair. FAQ Do I use the same validation key to validate all license codes? Yes, the validation key (and generation key) for the project remains the same; you use the same key to validate all license codes generated using the project. You can retrieve the validation key using the "Project" menu --> "Get Validation Key & Code" menu item. Can license codes generated using generation key from one project be validated using validation key of another project? No! Q. Is every generated license code unique? A. Yes, every license code generated by CryptoLicensing is guaranteed to be unique, even if you generate thousands of codes at a time. Q. What makes CryptoLicensing so secure? A. CryptoLicensing uses the latest cryptographic technology to generate and validate licenses. The cryptographic algorithm used is the RSA asymmetric key algorithm which can use upto 3072-bit keys. Given current computing power, it takes years to break a 3072-bit key. Q. Is is possible for a hacker to develop a keygen for my software? A. Impossible. The cryptographic algorithm used by CryptoLicensing consists of a pair of keys called as the generation key and the validation key. Data encrypted with one key can only be decrypted by the other key and vice versa. Licenses are generated using the generation key and validated using the validation key. Without the generation key, it is impossible to generate valid licenses. Q. What is the difference between validation key and generation key? Generation Key This key is used by CryptoLicensing Generator to generate encrypted license codes. This key is stored in the license project file, so the license project file must be kept secure and confidential and must be accorded the same care as any other critical asset such as source code. Validation Key This key is used for validating generated license codes. It is the same key displayed in the 'Get Validation Key And Code' dialog (Ctrl+K) and is used by your software when validating license codes (using LogicNP.CryptoLicensing.dll). Unlike the generation key, it is not necessary to keep this key secure and confidential. Q. Do I have to include the license project file (.licproj) with my software? A. No!!! This goes against the very essence of the security of the asymmetric cryptographic scheme because the project file contains both the validation and generation key. With your software, you only need to include the validation key which will be used to validate licenses generated by CryptoLicensing using the generation key. The license project file should be treated as any other valuable and confidential asset such as your source code. Q. Does the license service need the license project file? A. Yes. The license project file is needed whenever new licenses are generated (via the UI, via the API or via the license service). As just one example, the license service generates new machine-locked licenses when activated licenses are presented to it for activation, therefore the license service needs the license project file. Q. Is it possible to embed my own data in the generated licenses? A. Yes. You can embed any amount of additional data in the licenses. This data will have the same amount of security as the license code itself and will be tamper-proof. The embedded user data can be retrieved from your software. Q. What additional steps can I take to ensure that my software does not get cracked? A. There are many methods and techniques which can make it extremely difficult for a hacker to crack your software. See Writing Effective License Checking Code And Designing Effective Licenses for more information. Q. Why is the license service not working? A. The most common cause is not setting the CryptoLicense.LicenseServiceURL property before trying to validate a license. Make sure that this property is set to the correct URL where your license service is hosted. The most common cause after this is that the license project file on the web server where your license service is hosted is not the latest. This happens if you make changes to the license project (for example, set the 'Enable With Serials' setting for a profile), but don't upload the updated project file to your web server. Q. Why are my serials not working? Serial codes require the user of a license service. See Using Serial Codes for more details. Also see the earlier question 'Why is the license service not working?' Q. Is the same validation key used to validate license codes generated from different profiles. A. Yes. Profiles are just pre specified license settings for quickly generating licenses having those settings. The actual license code is still generated using the license project's cryptographic generation key and thus, can be validated using the project's validation key. Q. Why are changes made to a profile not getting saved? A. Simply changing license settings via UI and saving the license project does not save those license settings to the active profile. You must first save the license settings to a profile using the Save/Save As command from the Profiles menu (see above). Q. Why is validation of activated licenses failing from CryptoLicensing Generator, but works from my software? A. Make sure that you have specified the URL of the license service using the Project Properties Dialog. Also see the earlier question 'Why is the license service not working?' Q. How can I extend the trial period of my customer? A. To extend the evaluation period of the customer, simply send him a new license code specifying the desired evaluation limits. Evaluation information such as the current used days, executions, etc are stored in garbled form in a registry location which is derived from the license code. Therefore, when a new license code is used, the old evaluation information will not be used and a new evaluation period will be started.

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  • My Optimized Adam &amp; Eve

    - by MarkPearl
    Today I had a few minutes in the evening to go over my original Adam and Eve code… what I wanted to see tonight was if I could optimize the code any further… which I was pretty sure could be done. Ultimately what I wanted to find from the experiment was a balance between optimized code an reusable code. On the one hand I can put everything into a single function and end up with a totally unusable function that is extremely compressed, which would have big comebacks when making modifications at a later stage. Alternatively I could have many single line functions that are extremely loosely coupled but sparsely spaced and so would almost be to fragmented to grok. Ultimately I found with my current iteration something that I consider readable, yet compressed. Code below… // Learn more about F# at http://fsharp.net open System let people = [ ("Adam", None); ("Eve", None); ("Cain", Some("Adam", "Eve")); ("Abel", Some("Adam", "Eve")) ] // // Prints the details // let showDetails(person : string * (string * string) option) = let ParentsName = let parents = snd(person) match parents with | Some(dad, mum) -> "Father " + dad + " and Mother " + mum | None -> "Has no parents!" let result = fst(person) + Environment.NewLine + ParentsName result // // Searches an array of people and looks for a match of names // let findPerson(name : string, people : (string * (string * string) option) list) = // Try and find a match of the name let o = Seq.tryFind(fun person -> match name with | firstName when firstName = fst(person) -> true | _ -> false) people // Show the details based on the match result match o with | Option.Some(x) -> showDetails(Option.get(o)) | _ -> "Not Found" Console.WriteLine(findPerson("Cains", people)) Console.ReadLine()

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  • Formal Languages, Inductive Proofs &amp; Regular Expressions

    - by MarkPearl
    So I am slogging away at my UNISA stuff. I have just finished doing the initial once non stop read through the first 11 chapters of my COS 201 Textbook - “Introduction to Computer Theory 2nd Edition” by Daniel Cohen. It has been an interesting couple of days, with familiar concepts coming up as well as some new territory. In this posting I am going to cover the first couple of chapters of the book. Let start with Formal Languages… What exactly is a formal language? Pretty much a no duh question for me but still a good one to ask – a formal language is a language that is defined in a precise mathematical way. Does that mean that the English language is a formal language? I would say no – and my main motivation for this is that one can have an English sentence that is correct grammatically that is also ambiguous. For example the ambiguous sentence: "I once shot an elephant in my pyjamas.” For this and possibly many other reasons that I am unaware of, English is termed a “Natural Language”. So why the importance of formal languages in computer science? Again a no duh question in my mind… If we want computers to be effective and useful tools then we need them to be able to evaluate a series of commands in some form of language that when interpreted by the device no confusion will exist as to what we were requesting. Imagine the mayhem that would exist if a computer misinterpreted a command to print a document and instead decided to delete it. So what is a Formal Language made up of… For my study purposes a language is made up of a finite alphabet. For a formal language to exist there needs to be a specification on the language that will describe whether a string of characters has membership in the language or not. There are two basic ways to do this: By a “machine” that will recognize strings of the language (e.g. Finite Automata). By a rule that describes how strings of a language can be formed (e.g. Regular Expressions). When we use the phrase “string of characters”, we can also be referring to a “word”. What is an Inductive Proof? So I am not to far into my textbook and of course it starts referring to proofs and different types. I have had to go through several different approaches of proofs in the past, but I can never remember their formal names , so when I saw “inductive proof” I thought to myself – what the heck is that? Google to the rescue… An inductive proof is like a normal proof but it employs a neat trick which allows you to prove a statement about an arbitrary number n by first proving it is true when n is 1 and then assuming it is true for n=k and showing it is true for n=k+1. The idea is that if you want to show that someone can climb to the nth floor of a fire escape, you need only show that you can climb the ladder up to the fire escape (n=1) and then show that you know how to climb the stairs from any level of the fire escape (n=k) to the next level (n=k+1). Does this sound like a form of recursion? No surprise then that in the same chapter they deal with recursive definitions. An example of a recursive definition for the language EVEN would the 3 rules below: 2 is in EVEN If x is in EVEN then so is x+2 The only elements in the set EVEN are those that be produced by the rules above. Nothing to exciting… So if a definition for a language is done recursively, then it makes sense that the language can be proved using induction. Regular Expressions So I am wondering to myself what use is this all – in fact – I find this the biggest challenge to any university material is that it is quite hard to find the immediate practical applications of some theory in real life stuff. How great was my joy when I suddenly saw the word regular expression being introduced. I had been introduced to regular expressions on Stack Overflow where I was trying to recognize if some text measurement put in by a user was in a valid form or not. For instance, the imperial system of measurement where you have feet and inches can be represented in so many different ways. I had eventually turned to regular expressions as an easy way to check if my parser could correctly parse the text or not and convert it to a normalize measurement. So some rules about languages and regular expressions… Any finite language can be represented by at least one if not more regular expressions A regular expressions is almost a rule syntax for expressing how regular languages can be formed regular expressions are cool For a regular expression to be valid for a language it must be able to generate all the words in the language and no other words. This is important. It doesn’t help me if my regular expression parses 100% of my measurement texts but also lets one or two invalid texts to pass as well. Okay, so this posting jumps around a bit – but introduces some very basic fundamentals for the subject which will be built on in later postings… Time to go and do some practical examples now…

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  • Great Surprise &ndash; MSDN Ultimate

    - by MarkPearl
    So, I attended the Microsoft Community Evening. The attendance was better than I was expecting for December and we had our first Programming Languages Meeting where Gary did a great presentation on an intro to Ruby. The best surprize of the evening happened when I was about to leave, Robert MacLean asked me how we did our MS licensing – the fact being that we were about to reach the end of our empower license with Microsoft and that I had no idea how we were going to afford upgrading it early next year. Well, out comes a Microsoft Visual Studio Ultimate with MSDN 12 month subscription. An absolute awesome gift – thanks Robert! Best gift ever!

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  • Inversion of Control Resource

    - by MarkPearl
    Well… this is going to be another really short blog posting. I have been meaning to read more about IOC containers and came across this blog post which seemed to really explain the concept well – based on Castle Windsor. I also  enjoyed reading the replies about IOC on stack overflow and what it meant. If anyone knows of other good articles that explain the basics really well – wont you comment them to me.

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  • South African .Net Bloggers

    - by MarkPearl
    Where would I be without the inspiration of the following South African developers who are constantly contributing to the .NET community. Robert MacClean Hilton Giesenow Rubi Grobler Zayd Kara Zlatan Dzinic Dave Coates As well as the great input we get from the local Microsoft people.

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  • F# &ndash; Immutable List vs a Mutable Collection in Arrays

    - by MarkPearl
    Another day gone by looking into F#. Today I thought I would ramble on about lists and arrays in F#. Coming from a C# background I barely ever use arrays now days in my C# code – why you may ask – because I find lists generally handle most of the business scenario’s that I come across. So it has been an interesting experience with me keep bumping into Array’s & Lists in F# and I wondered why the frequency of coming across arrays was so much more in this language than in C#. Take for instance the code I stumbled across today. let rng = new Random() let shuffle (array : 'a array) = let n = array.Length for x in 1..n do let i = n-x let j = rng.Next(i+1) let tmp = array.[i] array.[i] <- array.[j] array.[j] <- tmp array   Quite simply its purpose is to “shuffle” an array of items. So I thought, why does it have the “a’ array'” explicitly declared? What if I changed it to a list? Well… as I was about to find out there are some subtle differences between array’s & lists in F# that do not exist in C#. Namely, mutability. A list in F# is an ordered, immutable series of elements of the same type, while an array is a fixed-size zero based, mutable collection of consecutive data elements that are all of the same type. For me the keyword is immutable vs mutable collection. That’s why I could not simply swap the ‘a array with ‘a list in my function header because then later on in the code the syntax would not be valid where I “swap” item positions. i.e. array.[i] <- array.[j] would be invalid because if it was a list, it would be immutable and so couldn’t change by its very definition.. So where does that leave me? It’s to early days to say. I don’t know what the balance will be in future code – will I typically always use lists or arrays or even have a balance, but time will tell.

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  • MSCRM Tax default to Zero

    - by MarkPearl
    I have been playing around with MSCRM4 lately. It has been interesting going. I had a problem getting the tax to reflect correctly, it was defaulting at zero. Eventually I found a solution after scouring the web for a while... see steps below…                 Add the following code to OnSave and OnLoad events of quotedetails form with (crmForm.all) { try { var dTax = (baseamount.DataValue - manualdiscountamount.DataValue) *15.5 /100;         tax.DataValue = dTax;         extendedamount.DataValue = baseamount.DataValue - manualdiscountamount.DataValue + tax.DataValue ; } catch(e) {         alert(e.message); } } // with Don’t forget to publish your changes once you are done and to test.

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  • Podcasting vs Stack Overflow vs Geekswithblogs

    - by MarkPearl
    For a few years now I have been looking for effective ways to be involved in the “community”. While there are a few community programming events in my area (Johannesberg), there isn’t too much face to face stuff – which has caused me to turn to the internet. My internet attempts have been varied – at first I took the passive approach of listening to tech podcasts. This was great for a while, but soon the content became semi-repetitive and a little boring. It seemed that the podcasts I was listening to all went round the same themes and speakers and while I am still a keen listener to several tech podcasts – it didn’t quench my thirst. So I began to be a bit more active – starting with stack overflow – where I would scan the site for questions that were in the realm of my ability to answer. It worked for a while but soon it began to be discouraging – there seems to be so many people that know so much more than me and are quicker at typing that I felt fairly ineffective. So while I still use Stack Overflow when I am in a pickle and need some help – it feels more like me taking from the community than giving anything. Which brought me to Geeks with blogs. Till I found GWB I hadn’t felt like I was an active part of a community. I had blogged before on Blogspot and Wordpress but hadn’t felt associated to the community. Now when I get a comment from someone on one of my GWB posts either thanking me or adding a bit more or correcting me, it makes me feel like I am contributing to a community. So well done GWB. Thanks for making a spot that makes me feel at home!

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  • Sound vs. Valid Argument

    - by MarkPearl
    Today I spent some time reviewing my Formal Logic course for my up coming exam. I came across a section that I have never really explored in any proper depth… the difference between a valid argument and a sound argument. Here go some notes I made… What is an argument? In this case we are not referring to a verbal fight, but more what we call a set of premise followed by a conclusion. Before we go further we need to understand what a premise is… a premise is a statement that an argument claims will induce or justify a conclusion. Think of a premise as an assumption that something is true. So, an argument can consist of one or more premises and a conclusion… When is an argument valid? An argument can be either valid or invalid. An argument is valid if, and only if, it is impossible for there to be a situation in which all it's premises are TRUE and it's conclusion is FALSE. It is generally easier to determine if an argument is invalid. Do this by applying the following… Assume that all the premises are true, then ask yourself if it is now possible for the conclusion to be false. If the answer is "yes," the argument is invalid. If it's "no," the argument is valid. Example 1… P1 – Mark is Tall P2 – Mark is a boy C –  Mark is a tall boy Walkthrough 1… Assume Mark is Tall is true and also assume that Mark is a boy. Based on these two premises, the conclusion is also true – Mark is a tall boy, thus the it is a valid argument. Let’s make this an invalid argument…   Example 2… P1 – Mark is Tall P2 – Mark is a boy C – Mark is a short boy Walkthrough 2… This would be an invalid argument, since from the premises we assume that Mark is tall and he is a boy, and then the conclusion goes against this by saying that Mark is short. Thus an invalid argument.   When is an argument sound? An argument is said to be sound when it is valid and all the premises are indeed true (not just assumed to be true). Rephrased, an argument is said to be sound when the conclusion will follow from the premises and the premises are indeed true in real life. In example 1 we were referring to a specific person, if we generalized it a bit we could come up with the following example.   Example 3 P1 – All people called Mark are tall P2 – I know a specific person called Mark C – He is a tall person   In this instance, it is a valid argument (we assume the premises are true, which leads to the conclusion being true), but the argument is NOT sound. In the real world there must be at least one person called Mark who is not tall. Something also to note, all invalid arguments are also unsound – this makes sense, if an argument is not valid, how on earth can it be true in the real world.   What happens when the premises contradict themselves? This is an interesting one… An argument is valid if, and only if, it is impossible for there to be a situation in which all it's premises are TRUE and it's conclusion is FALSE. When premises are contradictory, the argument is always valid because it is impossible for all the premises to be true at one time. Lets look at an example.. P1 - Elvis is dead P2 – Elvis is alive C – Laura is a woolly mammoth This is a valid argument, but not a sound one. Think about it. Is it possible to have a situation in which the premises are true and the conclusion is false? Sure, it's possible to have a situation in which the conclusion is false, but for the argument to be invalid, it has to be possible for the premises to all be true at the same time the conclusion is false. So if the premises can't all be true, the argument is valid. (If you still think the argument is invalid, draw a picture in which the premises are all true and the conclusion is false. Remember, there's only one Elvis, and you can't be both dead and alive.) For more info on this I suggest reading the following blog post.

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  • Lazy Evaluation &ndash; Why being lazy in F# blows my mind!

    - by MarkPearl
    First of all – shout out to Peter Adams – from the feedback I have gotten from him on the last few posts of F# that I have done – my mind has just been expanded. I did a blog post a few days ago about infinite sequences – I didn’t really understand what was going on with it, and I still don’t really get it – but I am getting closer. In Peter’s last comment he made mention of Lazy Evaluation. I am ashamed to say that up till then I had never heard about lazy evaluation – how can evaluation be lazy? I mean, I know about lazy loading and that makes sense… but surely something is either evaluated or not! Well… a bit of reading today and I have been enlightened to a point – if you do know of any good articles explaining lazy evaluation please send them to me. So what is lazy evaluation and why is it useful? Lazy evaluation is a process whereby the system only computes the values needed and “ignores” the computations not needed. I’m going out on a limb here, but with this explanation in hand, imagine the following C# code… public int CalculatedVal() { int Val1 = 0; int Val2 = 0; for (int Count = 0; Count < 1000000; Count++) { Val1++; } return Val2; }   Normally, even though Val1 is never needed, the system would loop 1000000 times and add 1 to the current value of Val1. Imagine if the system realized this and so just skipped this segment of code and instead did the following…. public int CalculatedVal() { int Val1 = 0; return Val2; }   A massive saving in computation and wasted effort. Now I am pretty sure it isn’t as simple as this but I think this is the basic idea. For a more detailed explanation of lazy evaluation in c#, Pedram Rezei has a wonderful post on lazy evaluation and makes some C# comparisons. I am not going to take any thunder from him by repeating everything he said since I think he did such a good job of explaining it himself. What I am interested in though is how in F# do you tell something to have lazy evalution, and how do you know if something will be eager or lazy by looking at it. I found this post was useful. From reading around F# by default uses eager evaluation unless explicitly told to use lazy evaluation. One exception to this is sequences, which are lazy by default. Now reading about lazy evaluation has helped me understand more about F# coding… From my understanding of F# because of its declarative nature, most of the actual code you are declaring properties and rules – very little code is actually saying do this right now - but when it comes to a “do this” code section, it then evaluates and optimizes code and applies the rules. So props to lazy evaluation and its optimizations…

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  • F# WPF Form &ndash; the basics

    - by MarkPearl
    I was listening to Dot Net Rocks show #560 about F# and during the podcast Richard Campbell brought up a good point with regards to F# and a GUI. In essence what I understood his point to be was that until one could write an end to end application in F#, it would be a hard sell to developers to take it on. In part I agree with him, while I am beginning to really enjoy learning F#, I can’t but help feel that I would be a lot further into the language if I could do my Windows Forms like I do in C# or VB.NET for the simple reason that in “playing” applications I spend the majority of the time in the UI layer… So I have been keeping my eye out for some examples of creating a WPF form in a F# project and came across Tim’s F# Twitter Stream Sample, which had exactly this…. of course he actually had a bit more than a basic form… but it was enough for me to scrap the insides and glean what I needed. So today I am going to make just the very basic WPF form with all the goodness of a XAML window. Getting Started First thing we need to do is create a new solution with a blank F# application project – I have made mine called FSharpWPF. Once you have the project created you will need to change the project type from a Console Application to a Windows Application. You do this by right clicking on the project file and going to its properties… Once that is done you will need to add the appropriate references. You do this by right clicking on the References in the Solution Explorer and clicking “Add Reference'”. You should add the appropriate .Net references below for WPF & XAMl to work. Once these references are added you then need to add your XAML file to the project. You can do this by adding a new item to the project of type xml and simply changing the file extension from xml to xaml. Once the xaml file has been added to the project you will need to add valid window XAML. Example of a very basic xaml file is shown below… <Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="F# WPF WPF Form" Height="350" Width="525"> <Grid> </Grid> </Window> Once your xaml file is done… you need to set the build action of the xaml file from “None” to “Resource” as depicted in the picture below. If you do not set this you will get an IOException error when running the completed project with a message along the lines of “Cannot locate resource ‘window.xaml’ You then need to tie everything up by putting the correct F# code in the Program.fs to load the xaml window. In the Program.fs put the following code… module Program open System open System.Collections.ObjectModel open System.IO open System.Windows open System.Windows.Controls open System.Windows.Markup [<STAThread>] [<EntryPoint>] let main(_) = let w = Application.LoadComponent(new System.Uri("/FSharpWPF;component/Window.xaml", System.UriKind.Relative)) :?> Window (new Application()).Run(w) Once all this is done you should be able to build and run your project. What you have done is created a WPF based window inside a FSharp project. It should look something like below…   Nothing to exciting, but sufficient to illustrate the very basic WPF form in F#. Hopefully in future posts I will build on this to expose button events etc.

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  • Expert F# &ndash; Pattern Matching with Adam and Eve

    - by MarkPearl
    So I am loving my Expert F# book. I wish I had more time with it, but the little time I get I really enjoy. However today I was completely stumped by what the book was trying to get across with regards to pattern matching. On Page 38 – Chapter 3, it briefly describes F# option values. On this page it gives the code snippet along the code lines below and then goes on to speak briefly about pattern matching... open System type 'a option = | None | Some of 'a let people = [ ("Adam", None); ("Eve", None); ("Cain", Some("Adam", "Eve")); ("Abel", Some("Adam", "Eve")) ] let showParents(name, parents) = match parents with | Some(dad, mum) -> printfn "%s has father %s, mother %s" name dad mum | None -> printfn "%s has no parents!" name Console.WriteLine(showParents("Adam", None))   Originally when I read this code I think I misunderstood the purpose of the example code. I for some reason thought that the showParents function would magically be parsing the people array and looking for a match of name and then showing the parents. But obviously it cannot do this since there is no reference to the people array in the showParents method. After rereading the page I realized that I had just combined the two segments of code together, possibly incorrectly, and that a better example would have been to have a code snippet like the following. let showParents(name, parents) = match parents with | Some(dad, mum) -> printfn "%s has father %s, mother %s" name dad mum | None -> printfn "%s has no parents!" name Console.WriteLine(showParents("Adam", None)) Console.WriteLine(showParents("Cain", Some("Adam", "Eve"))) Console.ReadLine()   However, what if I wanted to have a function that was passed a list of people and a name would then show the parents of the name if there were any, and if not would show that they had no parents… so that doesnt seem to difficult does it… lets look at my very unoptimized noob F# code to try and achieve this… open System let people = [ ("Adam", None); ("Eve", None); ("Cain", Some("Adam", "Eve")); ("Abel", Some("Adam", "Eve")) ] // // returns the name of the person // let showName(person : string * (string * string) option) = let name = fst(person) name // // Returns a string with the parents details or not // let showParents(itemData : string * (string * string) option) = let name = fst(itemData) let parents = snd(itemData) match parents with | Some(dad, mum) -> "Father " + dad + " and Mother " + mum | None -> "Has no parents!" // // Prints the details // let showDetails(person : string * (string * string) option) = Console.WriteLine(showName(person)) Console.WriteLine(showParents(person)) // // Check if the name matches the first portion of person // if so, return true, else return false // let nameMatch(name : string , person : string * (string * string) option) = match name with | x when x = fst(person) -> true | _ -> false // // Searches an array of people and looks for a match of names // let findPerson(name : string, people : (string * (string * string) option) list) = let o = Seq.tryFind(fun x -> nameMatch(name, x)) people if Option.isSome o then o else Option.None // // Try and find a person, if found show their details // else show no match // let FoundPerson = findPerson("Cain", people) match FoundPerson with | None -> Console.WriteLine("Not found") | Some(x) -> showDetails(x) Console.ReadLine() So, my code isn’t the cleanest but it did teach me a bit more F#. The area that I learnt about was the option keyword. The challenge being, if a match of the name isn’t found – and if a name is found but the person doesn’t have parents it should react accordingly. I’m pretty sure I can optimize this code quite a bit more and I think I may come back to it sometime in the future and relook at it, but for now at least I was able to achieve what I wanted.. and my brain has gone just that wee little bit more functional.

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  • International Radio Operators Alphabet in F# &amp; Silverlight &ndash; Part 2

    - by MarkPearl
    So the brunt of my my very complex F# code has been done. Now it’s just putting the Silverlight stuff in. The first thing I did was add a new project to my solution. I gave it a name and VS2010 did the rest of the magic in creating the .Web project etc. In this instance because I want to take the MVVM approach and make use of commanding I have decided to make the frontend a Silverlight4 project. I now need move my F# code into a proper Silverlight Library. Warning – when you create the Silverlight Library VS2010 will ask you whether you want it to be based on Silverlight3 or Silverlight4. I originally went for Silverlight4 only to discover when I tried to compile my solution that I was given an error… Error 12 F# runtime for Silverlight version v4.0 is not installed. Please go to http://go.microsoft.com/fwlink/?LinkId=177463 to download and install matching.. After asking around I discovered that the Silverlight4 F# runtime is not available yet. No problem, the suggestion was to change the F# Silverlight Library to a Silverlight3 project however when going to the properties of the project file – even though I changed it to Silverlight3, VS2010 did not like it and kept reverting it to a Silverlight4 project. After a few minutes of scratching my head I simply deleted Silverlight4 F# Library project and created a new F# Silverlight Library project in Silverlight3 and VS2010 was happy. Now that the project structure is set up, rest is fairly simple. You need to add the Silverlight Library as a reference to the C# Silverlight Front End. Then setup your views, since I was following the MVVM pattern I made a Views & ViewModel folder and set up the relevant View and ViewModels. The MainPageViewModel file looks as follows using System; using System.Net; using System.Windows; using System.Windows.Controls; using System.Windows.Documents; using System.Windows.Ink; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Animation; using System.Windows.Shapes; using System.Collections.ObjectModel; namespace IROAFrontEnd.ViewModels { public class MainPageViewModel : ViewModelBase { private string _iroaString; private string _inputCharacters; public string InputCharacters { get { return _inputCharacters; } set { if (_inputCharacters != value) { _inputCharacters = value; OnPropertyChanged("InputCharacters"); } } } public string IROAString { get { return _iroaString; } set { if (_iroaString != value) { _iroaString = value; OnPropertyChanged("IROAString"); } } } public ICommand MySpecialCommand { get { return new MyCommand(this); } } public class MyCommand : ICommand { readonly MainPageViewModel _myViewModel; public MyCommand(MainPageViewModel myViewModel) { _myViewModel = myViewModel; } public event EventHandler CanExecuteChanged; public bool CanExecute(object parameter) { return true; } public void Execute(object parameter) { var result = ModuleMain.ConvertCharsToStrings(_myViewModel.InputCharacters); var newString = ""; foreach (var Item in result) { newString += Item + " "; } _myViewModel.IROAString = newString.Trim(); } } } } One of the features I like in Silverlight4 is the new commanding. You will notice in my I have put the code under the command execute to reference to my F# module. At the moment this could be cleaned up even more, but will suffice for now.. public void Execute(object parameter) { var result = ModuleMain.ConvertCharsToStrings(_myViewModel.InputCharacters); var newString = ""; foreach (var Item in result) { newString += Item + " "; } _myViewModel.IROAString = newString.Trim(); } I then needed to set the view up. If we have a look at the MainPageView.xaml the xaml code will look like the following…. Nothing to fancy, but battleship grey for now… take careful note of the binding of the command in the button to MySpecialCommand which was created in the ViewModel. <UserControl x:Class="IROAFrontEnd.Views.MainPageView" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="400"> <Grid x:Name="LayoutRoot" Background="White"> <Grid.RowDefinitions> <RowDefinition/> <RowDefinition/> <RowDefinition/> </Grid.RowDefinitions> <TextBox Grid.Row="0" Text="{Binding InputCharacters, Mode=TwoWay}"/> <Button Grid.Row="1" Command="{Binding MySpecialCommand}"> <TextBlock Text="Generate"/> </Button> <TextBlock Grid.Row="2" Text="{Binding IROAString}"/> </Grid> </UserControl> Finally in the App.xaml.cs file we need to set the View and link it to the ViewModel. private void Application_Startup(object sender, StartupEventArgs e) { var myView = new MainPageView(); var myViewModel = new MainPageViewModel(); myView.DataContext = myViewModel; this.RootVisual = myView; }   Once this is done – hey presto – it worked. I typed in some “Test Input” and clicked the generate button and the correct Radio Operators Alphabet was generated. And that’s the end of my first very basic F# Silverlight application.

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  • Bug with Set / Get Accessor in .Net 3.5

    - by MarkPearl
    I spent a few hours scratching my head on this one... So I thought I would blog about it in case someone else had the same headache. Assume you have a class, and you are wanting to use the INotifyPropertyChanged interface so that when you bind to an instance of the class, you get the magic sauce of binding to do you updates to the UI. Well, I had a special instance where I wanted one of the properties of the class to add some additional formatting to itself whenever someone changed its value (see the code below).   class Test: INotifyPropertyChanged {     private string_inputValue;     public stringInputValue     {         get        {             return_inputValue;         }         set        {             if(value!= _inputValue)             {                 _inputValue = value+ "Extra Stuff";                 NotifyPropertyChanged("InputValue");                     }         }     }     public eventPropertyChangedEventHandler PropertyChanged;     public voidNotifyPropertyChanged(stringinfo)     {         if(PropertyChanged != null)         {             PropertyChanged(this, newPropertyChangedEventArgs(info));         }     } }   Everything looked fine, but when I ran it in my WPF project, the textbox I was binding to would not update? I couldn’t understand it! I thought the code made sense, so why wasn’t it working? Eventually StackOverflow came to the rescue, where I was told that it was a bug in the .Net 3.5 Runtime and that a fix was scheduled in .Net 4 For those who have the same problem, here is the workaround… You need to put the NotifyPropertyChanged method on the application thread! public string InputValue { get { return _inputValue; } set { if (value != _inputValue) { _inputValue = value + "Extra Stuff"; // // React to the type of measurement // Application.Current.Dispatcher.BeginInvoke((Action)delegate { NotifyPropertyChanged("InputValue"); }); } } }

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  • Creating my first F# program in my new &ldquo;Expert F# Book&rdquo;

    - by MarkPearl
    So I have a brief hour or so that I can dedicate today to reading my F# book. It’s a public holiday and my wife’s birthday and I have a ton of assignments for UNISA that I need to complete – but I just had to try something in F#. So I read chapter 1 – pretty much an introduction to the rest of the book – it looks good so far. Then I get to chapter 2, called “Getting Started with F# and .NET”. Great, there is a code sample on the first page of the chapter. So I open up VS2010 and create a new F# console project and type in the code which was meant to analyze a string for duplicate words… #light let wordCount text = let words = Split [' '] text let wordset = Set.ofList words let nWords = words.Length let nDups = words.Length - wordSet.Count (nWords, nDups) let showWordCount text = let nWords,nDups = wordCount text printfn "--> %d words in text" nWords printfn "--> %d duplicate words" nDups   So… bad start - VS does not like the “Split” method. It gives me an error message “The value constructor ‘Split’ is not defined”. It also doesn’t like wordSet.Count telling me that the “namespace or module ‘wordSet’ is not defined”. ??? So a bit of googling and it turns out that there was a bit of shuffling of libraries between the CTP of F# and the Beta 2 of F#. To have access to the Split function you need to download the F# PowerPack and hen reference it in your code… I download and install the powerpack and then add the reference to FSharp.Core and FSharp.PowerPack in my project. Still no luck! Some more googling and I get the suggestions I got were something like this…#r "FSharp.PowerPack.dll";; #r "FSharp.PowerPack.Compatibility.dll";; So I add the code above to the top of my Program.fs file and still no joy… I now get an error message saying… Error    1    #r directives may only occur in F# script files (extensions .fsx or .fsscript). Either move this code to a script file, add a '-r' compiler option for this reference or delimit the directive with '#if INTERACTIVE'/'#endif'. So what does that mean? If I put the code straight into the F# interactive it works – but I want to be able to use it in a project. The C# equivalent I would think would be the “Using” keyword. The #r doesn’t seem like it should be in the FSharp code. So I try what the compiler suggests by doing the following…#if INTERACTIVE #r "FSharp.PowerPack.dll";; #r "FSharp.PowerPack.Compatibility.dll";; #endif No luck, the Split method is still not recognized. So wait a second, it mentioned something about FSharp.PowerPack.Compatibility.dll – I haven’t added this as a reference to my project so I add it and remove the two lines of #r code. Partial success – the Split method is now recognized and not underlined, but wordSet.Count is still not working. I look at my code again and it was a case error – the original wordset was mistyped comapred to the wordSet. Some case correction and the compiler is no longer complaining. So the code now seems to work… listed below…#light let wordCount text = let words = String.split [' '] text let wordSet = Set.ofList words let nWords = words.Length let nDups = words.Length - wordSet.Count (nWords, nDups) let showWordCount text = let nWords,nDups = wordCount text printfn "--> %d words in text" nWords printfn "--> %d duplicate words" nDups  So recap – if I wanted to use the interactive compiler then I need to put the #r code. In my mind this is the equivalent of me adding the the references to my project. If however I want to use the powerpack in a project – I just need to make sure that the correct references are there. I feel like a noob once again!

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  • The DOS DEBUG Environment

    - by MarkPearl
    Today I thought I would go back in time and have a look at the DEBUG command that has been available since the beginning of dawn in DOS, MS-DOS and Microsoft Windows. up to today I always knew it was there, but had no clue on how to use it so for those that are interested this might be a great geek party trick to pull out when you want the awe the younger generation and want to show them what “real” programming is about. But wait, you will have to do it relatively quickly as it seems like DEBUG was finally dumped from the Windows group in Windows 7. Not to worry, pull out that Windows XP box which will get you even more geek points and you can still poke DEBUG a bit. So, for those that are interested and want to find out a bit about the history of DEBUG read the wiki link here. That all put aside, lets get our hands dirty.. How to Start DEBUG in Windows Make sure your version of Windows supports DEBUG. Open up a console window Make a directory where you want to play with debug – in my instance I called it C221 Enter the directory and type Debug You will get a response with a – as illustrated in the image below…   The commands available in DEBUG There are several commands available in DEBUG. The most common ones are A (Assemble) R (Register) T (Trace) G (Go) D (Dump or Display) U (Unassemble) E (Enter) P (Proceed) N (Name) L (Load) W (Write) H (Hexadecimal) I (Input) O (Output) Q (Quit) I am not going to cover all these commands, but what I will do is go through a few of them briefly. A is for Assemble Command (to write code) The A command translates assembly language statements into machine code. It is quite useful for writing small assembly programs. Below I have written a very basic assembly program. The code typed out is as follows mov ax,0015 mov cx,0023 sub cx,ax mov [120],al mov cl,[120]A nop R is for Register (to jump to a point in memory) The r command turns out to be one of the most frequent commands you will use in DEBUG. It allows you to view the contents of registers and to change their values. It can be used with the following combinations… R – Displays the contents of all the registers R f – Displays the flags register R register_name – Displays the contents of a specific register All three methods are illustrated in the image above T is for Trace (To execute a program step by step) The t command allows us to execute the program step by step. Before we can trace the program we need to point back to the beginning of the program. We do this by typing in r ip, which moves us back to memory point 100. We then type trace which executes the first line of code (line 100) (As shown in the image below starting from the red arrow). You can see from the above image that the register AX now contains 0015 as per our instruction mov ax,0015 You can also see that the IP points to line 0103 which has the MOV CX,0023 command If we type t again it will now execute the second line of the program which moves 23 in the cx register. Again, we can see that the line of code was executed and that the CX register now holds the value of 23. What I would like to highlight now is the section underlined in red. These are the status flags. The ones we are going to look at now are 1st (NV), 4th (PL), 5th (NZ) & 8th (NC) NV means no overflow, the alternate would be OV PL means that the sign of the previous arithmetic operation was Plus, the alternate would be NG (Negative) NZ means that the results of the previous arithmetic operation operation was Not Zero, the alternate would be ZR NC means that No final Carry resulted from the previous arithmetic operation. CY means that there was a final Carry. We could now follow this process of entering the t command until the entire program is executed line by line. G is for Go (To execute a program up to a certain line number) So we have looked at executing a program line by line, which is fine if your program is minuscule BUT totally unpractical if we have any decent sized program. A quicker way to run some lines of code is to use the G command. The ‘g’ command executes a program up to a certain specified point. It can be used in connection with the the reset IP command. You would set your initial point and then run the G command with the line you want to end on. P is for Proceed (Similar to trace but slightly more streamlined) Another command similar to trace is the proceed command. All that the p command does is if it is called and it encounters a CALL, INT or LOOP command it terminates the program execution. In the example below I modified our example program to include an int 20 at the end of it as illustrated in the image below… Then when executing the code when I encountered the int 20 command I typed the P command and the program terminated normally (illustrated below). D is for Dump (or for those more polite Display) So, we have all these assembly lines of code, but if you have ever opened up an exe or com file in a text/hex editor, it looks nothing like assembly code. The D command is a way that we can see what our code looks like in memory (or in a hex editor). If we examined the image above, we can see that Debug is storing our assembly code with each instruction following immediately after the previous one. For instance in memory address 110 we have int and 111 we have 20. If we examine the dump of memory we can see at memory point 110 CD is stored and at memory point 111 20 is stored. U is for Unassemble (or Convert Machine code to Assembly Code) So up to now we have gone through a bunch of commands, but probably one of the most useful is the U command. Let’s say we don’t understand machine code so well and so instead we want to see it in its equivalent assembly code. We can type the U command followed by the start memory point, followed by the end memory point and it will show us the assembly code equivalent of the machine code. E is for a bunch of things… The E command can be used for a bunch of things… One example is to enter data or machine code instructions directly into memory. It can also be used to display the contents of memory locations. I am not going to worry to much about it in this post. N / L / W is for Name, Load & Write So we have written out assembly code in debug, and now we want to save it to disk, or write it as a com file or load it. This is where the N, L & W command come in handy. The n command is used to give a name to the executable program file and is pretty simple to use. The w command is a bit trickier. It saves to disk all the memory between point bx and point cx so you need to specify the bx memory address and the cx memory address for it to write your code. Let’s look at an example illustrated below. You do this by calling the r command followed by the either bx or cx. We can then go to the directory where we were working and will see the new file with the name we specified. The L command is relatively simple. You would first specify the name of the file you would like to load using the N command, and then call the L command. Q is for Quit The last command that I am going to write about in this post is the Q command. Simply put, calling the Q command exits DEBUG. Commands we did not Cover Out of the standard DEBUG commands we covered A, T, G, D, U, E, P, R, N, L & W. The ones we did not cover were H, I & O – I might make mention of these in a later post, but for the basics they are not really needed. Some Useful Resources Please note this post is based on the COS2213 handouts for UNISA A Guide to DEBUG - http://mirror.href.com/thestarman/asm/debug/debug.htm#NT

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  • International Radio Operators Alphabet in F# &amp; Silverlight &ndash; Part 1

    - by MarkPearl
    So I have been delving into F# more and more and thought the best way to learn the language is to write something useful. I have been meaning to get some more Silverlight knowledge (up to now I have mainly been doing WPF) so I came up with a really simple project that I can actually use at work. Simply put – I often get support calls from clients wanting new activation codes. One of our main app’s was written in VB6 and had its own “security” where it would require about a 45 character sequence for it to be activated. The catch being that each time you reopen the program it would require a different character sequence, which meant that when we activate clients systems we have to do it live! This involves us either referring them to a website, or reading the characters to them over the phone and since nobody in the office knows the IROA off by heart we would come up with some interesting words to represent characters… 9 times out of 10 the client would type in the wrong character and we would have to start all over again… with this app I am hoping to reduce the errors of reading characters over the phone by treating it like a ham radio. My “Silverlight” application will allow for the user to input a series of characters and the system will then generate the equivalent IROA words… very basic stuff e.g. Character Input – abc Words Generated – Alpha Bravo Charlie After listening to Anders Hejlsberg on Dot Net Rocks Show 541 he mentioned that he felt many applications could make use of F# but in an almost silo basis – meaning that you would write modules that leant themselves to Functional Programming in F# and then incorporate it into a solution where the front end may be in C# or where you would have some other sort of glue. I buy into this kind of approach, so in this project I will use F# to do my very intensive “Business Logic” and will use Silverlight/C# to do the front end. F# Business Layer I am no expert at this, so I am sure to get some feedback on way I could improve my algorithm. My approach was really simple. I would need a function that would convert a single character to a string – i.e. ‘A’ –> “Alpha” and then I would need a function that would take a string of characters, convert them into a sequence of characters, and then apply my converter to return a sequence of words… make sense? Lets start with the CharToString function let CharToString (element:char) = match element.ToString().ToLower() with | "1" -> "1" | "5" -> "5" | "9" -> "9" | "2" -> "2" | "6" -> "6" | "0" -> "0" | "3" -> "3" | "7" -> "7" | "4" -> "4" | "8" -> "8" | "a" -> "Alpha" | "b" -> "Bravo" | "c" -> "Charlie" | "d" -> "Delta" | "e" -> "Echo" | "f" -> "Foxtrot" | "g" -> "Golf" | "h" -> "Hotel" | "i" -> "India" | "j" -> "Juliet" | "k" -> "Kilo" | "l" -> "Lima" | "m" -> "Mike" | "n" -> "November" | "o" -> "Oscar" | "p" -> "Papa" | "q" -> "Quebec" | "r" -> "Romeo" | "s" -> "Sierra" | "t" -> "Tango" | "u" -> "Uniform" | "v" -> "Victor" | "w" -> "Whiskey" | "x" -> "XRay" | "y" -> "Yankee" | "z" -> "Zulu" | element -> "Unknown" Quite simple, an element is passed in, this element is them converted to a lowercase single character string and then matched up with the equivalent word. If by some chance a character is not recognized, “Unknown” will be returned… I know need a function that can take a string and can parse each character of the string and generate a new sequence with the converted words… let ConvertCharsToStrings (s:string) = s |> Seq.toArray |> Seq.map(fun elem -> CharToString(elem)) Here… the Seq.toArray converts the string to a sequence of characters. I then searched for some way to parse through every element in the sequence. Originally I tried Seq.iter, but I think my understanding of what iter does was incorrect. Eventually I found Seq.map, which applies a function to every element in a sequence and then creates a new collection with the adjusted processed element. It turned out to be exactly what I needed… To test that everything worked I created one more function that parsed through every element in a sequence and printed it. AT this point I realized the the Seq.iter would be ideal for this… So my testing code is below… let PrintStrings items = items |> Seq.iter(fun x -> Console.Write(x.ToString() + " ")) let newSeq = ConvertCharsToStrings("acdefg123") PrintStrings newSeq Console.ReadLine()   Pretty basic stuff I guess… I hope my approach was right? In Part 2 I will look into doing a simple Silverlight Frontend, referencing the projects together and deploying….

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  • My Expert F# Book has now arrived!

    - by MarkPearl
    So it has finally arrived from Amazon. Expert F# by Don Syme, Adam Granicz & Antonio Cisternino. I got a note from the post office yesterday that I needed to collect a package from their offices. After paying a 10% customs fee (that I wasn’t expecting) I had my new Yellow & Black F# Book… it’s so shinny. Trust my luck though – I have a few university assignments due this week as well as a crazy week of work so it has been sitting on my desk for a day and I haven’t managed to get into it. Eventually I managed to take a few minutes this evening to page through it and it looks really good. I can’t wait! So my goal this week is to cover Chapter 2 (by the end of the weekend) and put the appropriate posts up. F# is slowly working on me but I am keen to get a deeper understanding of the language which I am hoping this book will help me achieve.

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