Re: [Haskell-cafe] Annoucing alternative to Text.Regex

8 Mar 2006

      Hello Chris,

Wednesday, March 8, 2006, 1:26:37 AM, you wrote:

CK> It takes the string form of the regular expression and uses Parsec to create a

he-he, i written the same thing (but very simple) 2 years ago :)  i
planned to submit it to the Parsec developers as an example of
double-Parsec usage :)

i think that it is a great lib, but not sure that it should completely
replace current lib. old lib is more appropriate for packed string,
new lib work directly with Haskell strings

one more interesting thing - generation of faster and simpler parsers
for simple regexps. just as example, code from my own program, that
parse filename wildcards. it translates simple patterns directly to
the "String->Bool" functions and use Regex library for more complex
patterns

-- |Compiled regexpr representation          EXAMPLE
data RegExpr = RE_End                     -- ""
             | RE_Anything                -- "*"
             | RE_FromEnd RegExpr         -- '*':"bc"
             | RE_AnyChar RegExpr         -- '?':"bc"
             | RE_Char    Char RegExpr    -- 'a':"bc"
             | RE_FullRE  Regex           -- "r[0-9][0-9]"

is_wildcard s  =  s `contains_one_of` "?*["

translate_RE re = "^"++ (replaceAll "*" ".*"
                        .replaceAll "?" "."
                        .replaceAll "$" "\\$"
                        .replaceAll "[[[" "[^"   
                        .replaceAll "^" "\\^"
                        .replaceAll "[^" "[[["   
                        .replaceAll "+" "\\+"
                        .replaceAll "." "\\.") re ++"$"

compile_RE s  =  case s of
  ""     -> RE_End
  "*"    -> RE_Anything
  '*':cs -> if ('*' `elem` cs) || ('[' `elem` cs)
              then RE_FullRE  (mkRegex$ translate_RE$ s)
              else RE_FromEnd (compile_RE$ reverse$   s)
  '[':cs -> RE_FullRE   (mkRegex$ translate_RE$ s)
  '?':cs -> RE_AnyChar  (compile_RE cs)
  c  :cs -> RE_Char   c (compile_RE cs)

match_RE re s  =  case re of
  RE_End        -> null s
  RE_Anything   -> True
  RE_FullRE   r -> isJust (matchRegex r s)
  RE_FromEnd  r -> match_RE r (reverse s)
  RE_AnyChar  r -> case s of
                     ""   -> False
                     _:xs -> match_RE r xs
  RE_Char   c r -> case s of
                     ""   -> False
                     x:xs -> x==c && match_RE r xs

match re {-s-}  =  match_RE (compile_RE re) {-s-}

{-# NOINLINE translate_RE #-}

-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin@gmail.com

Re: [Haskell-cafe] Annoucing alternative to Text.Regex

Bulat Ziganshin