Avoiding symbol capture when using macros to generate functions (or other macros)

Posted by Rob Lachlan on Stack Overflow See other posts from Stack Overflow or by Rob Lachlan
Published on 2010-05-28T05:10:27Z Indexed on 2010/05/28 7:51 UTC
Read the original article Hit count: 467

Filed under:

macros

|

clojure

|

symbol-capture

I'm a bit confused as to exactly when symbol capture will occur with clojure macros. Suppose that I have a macro which defines a function from keywords. In this trivial example,

(defmacro foo [keywd1 keywd2] `(defn ~(symbol (name keywd1)) 
                  [~(symbol (name keywd2))] (* 2 ~(symbol (name keywd2)))))

I call (foo :bar :baz), and this gets expanded into (defn bar [baz] (* 2 baz)).

So now the question -- can this lead to symbol capture? If so, under what circumstances? I know that it's preferred to use gensym (e.g. bar#) to prevent symbol capture, but in some cases (not many, but still) I'd like to have a pretty macro-expansion, without the auto-generated symbols.

Bonus question: does the answer change if we are considering a macro that creates macros?

© Stack Overflow or respective owner

Related posts about macros

"macros have been disabled" message in Word 2007 but no macros

as seen on Super User - Search for 'Super User'
Hi there, I open a .doc file in Word 2007 (sorry I am unable to supply the .doc) which pops up with a message above the document "Security warning: Macros have been disabled" but there are no macros shown in the macros listing and no functionality displayed in the VBScript editor. Why does Word… >>> More
Avoiding symbol capture when using macros to generate functions (or other macros)

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm a bit confused as to exactly when symbol capture will occur with clojure macros. Suppose that I have a macro which defines a function from keywords. In this trivial example, (defmacro foo [keywd1 keywd2] `(defn ~(symbol (name keywd1)) [~(symbol (name keywd2))] (* 2 ~(symbol… >>> More
Macros's that define macros

as seen on Stack Overflow - Search for 'Stack Overflow'
Does anyone know how to pull off something like this... I have alot of repetitive macros as : - #define MYMACRO1(x) Do1(x) #define MYMACRO2(x,y) Do2(x, y) #define MYNEXTMACRO1(x) Do1(x) #define MYNEXTMACRO2(x,y) Do2(x, y) The code above works fine, but I want to write a macro… >>> More
Macros in macros (C++)

as seen on Stack Overflow - Search for 'Stack Overflow'
Is it possible to put a macro in a macro in c++? Something like: #define Something\ #ifdef SomethingElse\ //do stuff \ #endif\ I tried and it didn't work so my guess is it doesn't work, unless there's some sort of syntax that can fix it? >>> More
makefile: how to call macros in macros

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello, I have the following macros in my make file: pdf: // do something clean: // just another fancy thing No I want to declare a macro all: which include (or call) the makros above. The following thing doesn't work: all: pdf: clean: I don't want to repeat the code from pdf:… >>> More

Related posts about clojure

StackOverflow in compojure web project

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi I've been playing around with clojure and have been using it to build a simple little audio player. The strange thing is that sometimes, maybe one out of twenty, when contact the server I will get the following error: 2010-04-20 15:33:20.963::WARN: Error for /control java.lang.StackOverflowError … >>> More
Wrong number of args passed to: repl$repl

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I have a trouble with a compojure "Getting started" example that I do not seem to understand. When I run the example from http://weavejester.github.com/compojure/docs/getting-started.html ...I get the following error at the lein repl step: ~/hello-www> lein repl src/hello_www/core.clj Exception… >>> More
Setting the Classpath and Accessing code from book: Programming Clojure

as seen on Stack Overflow - Search for 'Stack Overflow'
(I posted this same question on the Clojure list but haven't got an answer yet. Is anyone here ready to help?) I am going through Programming Clojure and I recently downloaded the code from the books official website. For other utils I can do, for example, (require 'clojure.contrib.str-utils) and… >>> More
How can I define a clojure type that implements the servlet interface?

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm attempting to use deftype (from the bleeding-edge clojure 1.2 branch) to create a java class that implements the java Servlet interface. I would expect the code below to compile (even though it's not very useful). (ns foo [:import [javax.servlet Servlet ServletRequest ServletResponse]]) (deftype… >>> More
Stack overflow in compojure web project

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi I've been playing around with clojure and have been using it to build a simple little audio player. The strange thing is that sometimes, maybe one out of twenty, when contacting the server I will get the following error: 2010-04-20 15:33:20.963::WARN: Error for /control java.lang.StackOverflowError … >>> More