Re: unhandled constant?

[Han-Wen Nienhuys]

On Fri, Jan 31, 2020 at 3:58 PM Linus Björnstam
<address@hidden> 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 - address@hidden - http://www.xs4all.nl/~hanwen
> >
> >



-- 
Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen