Re: match-record

["Ludovic Courtès" <ludo@gnu.org>]

Hi Aleksandr,

Aleksandr Vityazev <avityazev@posteo.org> skribis:

> Before cc9ee514e37f6ec74dd9cab91a13d51f7b8d47e7 commit the code below
> worked:
>
> #+begin_src scheme :scheme guile :season guile
>
> (define (iwd-etc-service config)
>   (match-record config <iwd-configuration> (config)
>     `(("iwd/main.conf"
>        ,(apply mixed-text-file
>                "main.conf"
>                (serialize-ini-config config))))))
> #+end_src
>
>
> then this lead to an error:
> Syntax error:
> test.scm:109:44: lookup-field: unknown record type field in subform
> config of (lookup-field config (+ 1 (+ 1 (+ 1 0))) ())
>
>
> If you fix the code to the following one, it will work. 
>
> #+begin_src scheme :scheme guile :season guile
>
> (define (iwd-etc-service cfg)
>   (match-record cfg <iwd-configuration> (config)

[...]

> Should the code from the first block work, or should I not write it that
> way?

You have to write it that way.  (Though I would recommend a different
name for the field anyway, maybe ‘raw-file’?)

This is due to how “literals” are matched in syntax-{case,rules} (info
"(guile) Syntax Rules"):

     A literal matches an input expression if the input expression is an
  identifier with the same name as the literal, and both are unbound(1).

Here, because of the ‘config’ parameter, one of the two identifiers was
bound while the other is not, hence the match error.

HTH!

Ludo’.