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From: David Kastrup <dak@gnu.org>
To: Han-Wen Nienhuys <hanwenn@gmail.com>
Cc: lilypond-devel <lilypond-devel@gnu.org>,
	Guile Devel <guile-devel@gnu.org>
Subject: Re: definitions in macros?
Date: Sun, 22 Mar 2020 22:09:25 +0100	[thread overview]
Message-ID: <87v9mw9jwa.fsf@fencepost.gnu.org> (raw)
In-Reply-To: <CAOw_e7bVfgmrMf-ZtjF4zJqESLS1Y6CbHNztxcvfiEYwX5PzwQ@mail.gmail.com> (Han-Wen Nienhuys's message of "Sun, 22 Mar 2020 20:07:11 +0100")

Han-Wen Nienhuys <hanwenn@gmail.com> 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



  parent reply	other threads:[~2020-03-22 21:09 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-22 19:07 definitions in macros? Han-Wen Nienhuys
2020-03-22 19:16 ` Matt Wette
2020-03-22 21:09 ` David Kastrup [this message]
2020-03-23  7:21   ` Han-Wen Nienhuys

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