[antlr-interest] Re: CLI with ANTLR - best practice
idontwantanidwith2000init
idontwantanidwith2000init at yahoo.com
Fri Apr 9 12:49:22 PDT 2004
about unput, taken from jguru faq:
Question Can I push back the most recently read token into the
input stream?
Topics Tools:ANTLR:Recognition:Lookahead,
Tools:ANTLR:Recognition:Syntactic predicates
Author Terence Parr PREMIUM
Created Oct 27, 2001
Answer
You are thinking in terms of the old one-token-of-lookahead type
parser generators without backtracking capabilities. ANTLR
specifically provides a mechanism to lookahead ahead a fixed amount,
k, or infinitely via syntactic predicates (a selective programmer-
controlled form of backtracking). You can tell ANTLR to try out an
alternative and back up to retry the next potentially viable
alternative if that one fails. It's like specifying the infinite
lookahead language that predicts an alternative.
--- In antlr-interest at yahoogroups.com, "thierryj8" <thierryj8 at y...>
wrote:
> Best practice for CLI in Lex&Yacc, O'Reilly:
>
> ".. In order to scan the command line rather than a file, we must
> rewrite input() and unput()..." (p38),
>
> "...The input routine handles calls from the lexer to obtain
> characters" (p41),
>
> "...The unput() routine handles calls from the lexer to "push back"
> characters into the input stream." (p41)
>
> Input() treats the CLI end of line as the end of file. Is there an
> equivalent in ANTLR?
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