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Re: unhandled constant?

From: Linus Björnstam
Subject: Re: unhandled constant?
Date: Fri, 31 Jan 2020 15:57:41 +0100
User-agent: Cyrus-JMAP/3.1.7-781-gfc16016-fmstable-20200127v1

Guile1.8's macros are run-time macros: they are executed directly and not 
transformed to output code that is then compiled. That is the reason why your 
code works: to newer guiles the (inner ...) is only available at expansion 
time. The macro output is trying to call code that does not exist at runtime!

For this to be working code the (inner ...) function needs to be available in 
the macro expansion. I didn't read through exactly what you are trying to do, 
but try outputting a let:

`(let ((inner (lambda (n v) (set ! ...))))
  (inner ,name ,value))

I doubt you can make the old code work in newer guiles, since I doubt any 
scheme is a s lax about expansion time and macro time separation.
  Linus Björnstam

On Wed, 29 Jan 2020, at 00:08, Han-Wen Nienhuys wrote:
> Some of the lilypond Scheme files do the following:
> (define decl '())
> (define (make-var n v) (list "var" n v))
> (defmacro define-session (name value)
>   (define (inner n v)
>     (set! decl
>         (cons
>          (make-var n v)
>          decl))
>     )
>   `(,inner ',name ,value))
> (define-session foo 1)
> (display decl)
> (newline)
> In GUILE 2.2, this yields
> ;;; WARNING: compilation of /home/hanwen/vc/lilypond/q.scm failed:
> ;;; unhandled constant #<procedure inner (a b)>
> What does this error message mean, and what should I do to address the 
> problem?
> -- 
> Han-Wen Nienhuys - address@hidden -

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