What is wrong with this list comprehension code?

Posted by suresh on Stack Overflow See other posts from Stack Overflow or by suresh
Published on 2012-03-26T22:20:08Z Indexed on 2012/03/26 23:30 UTC
Read the original article Hit count: 175

Filed under:

haskell

My aim is to list all elements of the array a whose values are greater than their index positions. I wrote a Haskell code like this.

[a|i<-[0..2],a<-[1..3],a!!i>i]

When tested on ghci prelude prompt, I get the following error message which I am unable to understand.

No instance for (Num [a]) arising from the literal 3 at <interactive>:1:20 Possible fix: add an instance declaration for (Num [a])

Related posts about haskell

Learning Haskell: How to remove an item from a List in Haskell

as seen on Stack Overflow - Search for 'Stack Overflow'
Trying to learn Haskell. I am trying to write a simple function to remove a number from a list without using built-in function (delete...I think). For the sake of simplicity, let's assume that the input parameter is an Integer and the list is an Integer list. Here is the code I have, Please tell me… >>> More
Using Data.Heap in Haskell, or reading Haskell docs for a beginner

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to use Haskells Data.Heap module, but I'm incapable of even using it with integers. The only heap I've been capable of using is "empty", which does not take any arguments. Later on I'll figure out how to instance for my needs, but for now I'd be glad if I was even able to test it with… >>> More
What kind of things are easy in Haskell and hard in Scala, and vice versa?

as seen on Programmers - Search for 'Programmers'
There has been some intermingling of Scala and Haskell communities, and I have noticed now and then people commenting on stuff that's supposed to be easy in Haskell and hard and Scala. Less often (maybe because I read Scala questions, not Haskell ones), I see someone mentioning that something in Scala… >>> More
Haskell's cabal dependency problem with happy

as seen on Programmers - Search for 'Programmers'
I have problems installing ghc-mod on my linux machine. cabal worries about "happy" not being available in versione = 1.17: $ cabal install ghc-mod Resolving dependencies... [1 of 1] Compiling Main ( /tmp/haskell-src-exts-1.14.0-1357/haskell-src-exts-1.14.0/Setup.hs, /tmp/haskell-src-exts-1… >>> More
Understanding Haskell's fibonacci

as seen on Stack Overflow - Search for 'Stack Overflow'
fibs :: [Int] fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)] This generates the Fibonacci sequence. I understand the behaviour of the guards, of :, zip and tail, but I don't understand <-. What is it doing here? >>> More

Developer IT

What is wrong with this list comprehension code? - Developer IT

What is wrong with this list comprehension code?

haskell

Related posts about haskell

Learning Haskell: How to remove an item from a List in Haskell

Using Data.Heap in Haskell, or reading Haskell docs for a beginner

What kind of things are easy in Haskell and hard in Scala, and vice versa?

Haskell's cabal dependency problem with happy

Understanding Haskell's fibonacci

Categories cloud