Re: PEG tutorial example doesnt work

Tomas Volf <[email protected]> Tue, 13 Aug 2024 01:38:01 +0200
Newsgroups	gmane.lisp.guile.user
Message-ID	<Zrqc2S7skODl0wY9@ws>
Hello,

On 2024-08-11 21:52:42 -0500, Diego Antonio Rosario Palomino wrote:
> Hello, i am a new scheme user trying to exploit the peg library but have
> encountered the following error :
>
> guile c.scm
> ;;; note: source file /home/diego/Documents/Guile/c.scm
> ;;;       newer than compiled
> /home/diego/.cache/guile/ccache/3.0-LE-8-4.6/home/diego/Documents/Guile/c.scm.go
> ;;; note: auto-compilation is enabled, set GUILEAUTO_COMPILE=0
> ;;;       or pass the --no-auto-compile argument to disable.
> ;;; compiling /home/diego/Documents/Guile/c.scm
> ;;; /home/diego/Documents/Guile/c.scm:20:57: warning: possibly unbound
> variable `⇒'
> ;;; compiled
> /home/diego/.cache/guile/ccache/3.0-LE-8-4.6/home/diego/Documents/Guile/c.scm.go
> Backtrace:
> In ice-9/boot-9.scm:
>   1752:10  6 (with-exception-handler   #:unwind?  # )
> In unknown file:
>            5 (apply-smob/0 #<thunk 7fcf881b52a0>)
> In ice-9/boot-9.scm:
>     724:2  4 (call-with-prompt   #<procedure default-prompt-handle…>)
> In ice-9/eval.scm:
>     619:8  3 ( #(#(#<directory (guile-user) 7fcf881b9c80>)))
> In ice-9/boot-9.scm:
>    2836:4  2 (save-module-excursion )
>   4388:12  1 ()
> In /home/diego/Documents/Guile/c.scm:
>     20:57  0 (_)
>
> /home/diego/Documents/Guile/c.scm:20:57: Unbound variable: ⇒

The arrow character in the documentation is a stand in meaning that A returns
B.

So in this example:

    (match-pattern cfunc "int square(int a) { return a*a;}") ⇒
    (32
     (cfunc (ctype "int")
            (cname "square")
            (cargs (carg (ctype "int") (cname "a")))
            (cbody (cstatement "return a*a"))))

It means that

    (match-pattern cfunc "int square(int a) { return a*a;}")

Returns this value:

    (32
     (cfunc (ctype "int")
            (cname "square")
            (cargs (carg (ctype "int") (cname "a")))
            (cbody (cstatement "return a*a"))))

This is used fairly commonly across Scheme info pages, so it is good thing to
know.

Hope this helps,
Tomas

--
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.
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