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Re: definitions in macros?

From: David Kastrup
Subject: Re: definitions in macros?
Date: Sun, 22 Mar 2020 22:09:25 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

Han-Wen Nienhuys <address@hidden> writes:

> Hi there,
> in my quest to get lilypond working with GUILE 2+, I've hit another
> stumbling block.
> In order to make compilation with GUILE 2+ working, we have to move
> away from runtime symbol definition (ie. module-define! calls).
> In the code below, it looks like only one of the two definitions in
> the body of my-macro-new takes effect. Is this expected, and if so,
> why?
> (defmacro-public my-macro-old (command-and-args . definition)
>   (module-define! (current-module) 'x1 "I am X1\n")
>   (module-define! (current-module) 'x2 "I am X2\n"))
> (defmacro-public my-macro-new (command-and-args . definition)
>     `(define p "i am P\n")
>     `(define q "i am Q\n"))

This is very much expected.  The macro body contains two side-effect
free expressions (namely quoted lists) and returns the last one which is

(define q "i am Q\n")

This then gets evaluated at run time, defining q .

You probably wanted something like
  `(begin (define p ...) (define q ...))

as your body (and return expression) instead.

> (my-macro-old 1 2)
> (my-macro-new 1 2)
> (display x1)
> (display x2)
> (display q)
> (display p)
> thanks,

David Kastrup

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