Is it possible in Lisp to undefine Macros and Functions?

Question

While using the REPL it would be helpful to undefine defined functions and macros, exspecially if you tried to make a macro for something, and then simulate it as function, and the macro is called everytime. Is it possible in Common Lisp to undefine?

Also see [How to delete variable/forms in Lisp?](http://stackoverflow.com/q/21231775/1281433) — Joshua Taylor, Feb 26 '14 at 17:34

score 18 · Accepted Answer · edited Feb 26 '14 at 11:16

18

Yes, you can use fmakunbound for this.

It works for both functions and macros. Here's an example REPL session:

CL-USER> (defun add (n m) (+ n m))
ADD        
CL-USER> (add 1 2)
3
CL-USER> (fmakunbound 'add)
ADD
CL-USER> (add 1 2)
; [snip]
; Evaluation aborted on #<UNDEFINED-FUNCTION ADD {C3305F1}>.

Note that it really is fmak rather than fmake. That still trips me up from time to time.

edited Feb 26 '14 at 11:16

lurker

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answered Feb 26 '14 at 01:38

jbm

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In clisp-REPL I only type "(fm" and tabulator, so I don't have to know if fmak or fmake. – porky11 Feb 26 '14 at 10:32
In my case, for some reason, the macro is still defined after calling fmakunbound. What could be the reason? – Philipp Ludwig Jun 19 '23 at 18:18

score 12 · Answer 2 · answered Feb 26 '14 at 08:14

Undefining a macro or function does not mean this change spreads through the code.

If you have a macro and want to redefine it as a function, then you also have to recompile the code which used the macro.

Note that if you compile code with certain optimizations (inlining), you need to recompile even more code. Even redefined functions might have no effect, until the using code also gets recompiled.

Is it possible in Lisp to undefine Macros and Functions?

2 Answers2

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