Hi,
using alex+happy, how could I parse lines like these?
> "mr <username> says <message>\n"
where both <username> and <message> may contain arbitrary characters (except
eol)?
If I make lexer tokens
> "mr " { T_Mr }
> " says " { T_Says }
> \r?\n { T_Eol }
> . { T_Char $$ }
and parser
> 'mr ' { T_Mr }
> ' says ' { T_Says }
> eol { T_Eol }
> char { T_Char }
...
> line :: { (String, String) }
> : 'mr ' string ' says ' string eol { ($2, $4) }
> string :: { String }
> : char { [ $1 ] }
> | char string { $1 : $2 }
then I get error when <username> or <message> contain "mr "
substrings, because parser encounters T_Mr token.
Workaround is mention all small tokens in my <string> definition:
> string :: { String }
> : { [] }
> | 'mr ' string { "mr " ++ $2 }
> | ' says ' string { " says " ++ $2 }
> | char string { $1 : $2 }
but that is weird and I'm sure there is a better way.
Thanks for advance,
Roman.
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
