RE: [Chicken-users] LALR parser examples

[Dominique Boucher]

Hi Joel!

> I'm looking for LALR (egg) parser examples. Can you share any? An  
> example of using a lexer like Silex (egg) with LALR would be most  
> helpful.

See below:

> (require 'lalr)
> 
> (define parser
>    (lalr-parser
>     ;; terminal symbols
>     (ABOVE AGO ALERT AND ARRAY ARRAY-NUMERIC
>            <= < >= > <> .. - + * / = [ (.  .) ] ( ) . , ; : @ ^ )
>     ...
> 
> How do I quote the parens and brackets above and use them later? Is  
> that even possible without renaming them to L-BRACKET, etc.?

Terminals can only be denoted by Scheme symbols. So yes, you'll have to 
rename all special characters to LBRACKET, RBRACKET, SEMICOLON, etc. A Silex

lexer definition that would interface with parsers generated by LALR 
would thus look like:

-------------------------- lexer.l
; some definitions ...

digit [0-9]

%% 

;; Skip whitespaces
[ \t\n]+  (yycontinue)

;; Tokens that are also Scheme symbols
("<=" | "<" | ">=" | ">" | "<>" | "-" | "+" | "*" | "/" | "=")
(string->symbol (yytext))

{digit}+   (cons 'INTEGER (string->number (yytext)))

;; special punctuation
"["   'LBRACKET
"]"   'RBRACKET
"("   'LPAREN
")"   'RPAREN
"."   'DOT
";"   'SEMICOLON

;; ... etc.

;; end of input
<<EOF>> '*eoi*
--------------------------


> If you could show me how to add parenthesis to your simple grammar  
> example it would be most helpful!

There is a more involved example that comes with the standard distribution
of LALR:

http://www.iro.umontreal.ca/~boucherd/Lalr/documentation/lalr.html

Cheers!
Dominique