Re: unhandled constant?

[Han-Wen Nienhuys <hanwenn@gmail.com>]

On Fri, Jan 31, 2020 at 3:58 PM Linus Björnstam
<linus.bjornstam@veryfast.biz> wrote:
>
> 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!

When is the code executed?  If have complex set of macros to define a
special type of functions (so called markup commands).  Some of these
refer to other markup commands through a macro.

What I can observe that some of the functions involved are not called
during the compilation, but others are.

In particular, the function that registers a markup command using something like

  (module-define! (current-module)
      (string->symbol (format #f "~a-markup" name))   defn))

but this function is not called during the compile

There is a convenience macro that is called within some function
bodies, that does get called. Unfortunately, the latter convenience
macro is expanded and then executed; the execution tries to then do

   (module-ref (current-module)
      (string->symbol (format #f "~a-markup" name)

which fails.



> 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 - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen
> >
> >



-- 
Han-Wen Nienhuys - hanwenn@gmail.com - http://www.xs4all.nl/~hanwen