Re: Obscure error message from 2.25.0

[Jean Abou Samra]

Le 15/01/2023 à 20:20, Graham King a écrit :
> I've just run convert-ly on a 600+ line file and its \include files, from 
> 2.19.40 to 2.25.0.  Nothing seemed to change apart from the \version statement, 
> but on trying to compile the file, I get:
>
> Processing `/tmp/....ly'
> Parsing...ERROR: In procedure %resolve-variable:
> Unbound variable: %
> Exited with return code 1.
>
> Does this point to an obvious problem?



You probably tried to use LilyPond comment syntax in a Scheme function.
Scheme comments start with ';' not '%'.

With Guile 1, as used in LilyPond 2.22, it happens that

#(define (func)
   % a bunch of unbound variables
   'x)

#(display (func))


"works" and prints "x". This is weird. The function body has several
expressions: %, a, ..., 'x, where all the ones before 'x are references
to variables called '%', 'a', ... In Scheme, the expressions before the
last one in a function body are evaluated only for their side effects, the
result is discarded. It seems that Guile 1 somehow detects that a
simple variable can't have a side effect and removes it, even
though it would trigger an error if it were evaluated.

We're on Guile 2 now, and it doesn't have this obscure behavior.

Best,
Jean

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