PEG tutorial example doesnt work

PEG tutorial example doesnt work

[Diego Antonio Rosario Palomino]

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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: ⇒

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(define-peg-string-patterns
  "cfunc <-- cSP ctype cSP cname cSP cargs cLB cSP cbody cRB
ctype <-- cidentifier
cname <-- cidentifier
cargs <-- cLP (! (cSP cRP) carg cSP (cCOMMA / cRP) cSP)* cSP
carg <-- cSP ctype cSP cname
cbody <-- cstatement *
cidentifier <- [a-zA-z][a-zA-Z0-9_]*
cstatement <-- (!';'.)*cSC cSP
cSC < ';'
cCOMMA < ','
cLP < '('
cRP < ')'
cLB < '{'
cRB < '}'
cSP < [ \t\n]*")


(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"))))
        
        
(match-pattern cfunc "int mod(int a, int b) { int c = a/b;return a-b*c; }") ⇒
(52
 (cfunc (ctype "int")
        (cname "mod")
        (cargs (carg (ctype "int") (cname "a"))
               (carg (ctype "int") (cname "b")))
        (cbody (cstatement "int c = a/b")
               (cstatement "return a- b*c"))))

Re: PEG tutorial example doesnt work

[Tomas Volf]

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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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