Based on my experiments, it appears that parser-tools/lex picks the rule with the longest match, breaking ties in favor of the rule appearing first. As far as I can tell, this fact is not documented in the lexer manual. It says:
"Produces a function that takes an input-port, matches the re’s against the buffer, and returns the result of executing the corresponding action-expr." Here's the text of my proposed commit. Unless I see a comment to the contrary, I'll commit this later today or tomorrow. Thanks! John >From eefa87cd51cc579ef4762e6986671797e0473718 Mon Sep 17 00:00:00 2001 From: John Clements <[email protected]> Date: Wed, 1 May 2013 07:51:40 -0700 Subject: [PATCH] specified match precedence in lexer... hope I'm right --- collects/parser-tools/parser-tools.scrbl | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff --git a/collects/parser-tools/parser-tools.scrbl b/collects/parser-tools/parser-tools.scrbl index cb3a84f..9bc5ef5 100644 --- a/collects/parser-tools/parser-tools.scrbl +++ b/collects/parser-tools/parser-tools.scrbl @@ -51,8 +51,10 @@ style lexer and parser generators. (id datum ...)])]{ Produces a function that takes an input-port, matches the - @racket[re]'s against the buffer, and returns the result of - executing the corresponding @racket[action-expr]. + @racket[re] patterns against the buffer, and returns the result of + executing the corresponding @racket[action-expr]. When multiple + patterns match, a lexer will choose the longest match, breaking + ties in favor of the rule appearing first. @margin-note{The implementation of @racketmodname[syntax-color/racket-lexer] contains a lexer for the @racketmodname[racket] language. -- 1.7.7.5 (Apple Git-26) ____________________ Racket Users list: http://lists.racket-lang.org/users
