RegToAlex.hs

{-
    BNF Converter: Regular expression pretty printer
    Copyright (C) 2004  Author:  BNF Converter, Aarne Ranta

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-}

module RegToAlex (printRegAlex) where

-- modified from pretty-printer generated by the BNF converter

import AbsBNF
import Data.Char

-- the top-level printing method
printRegAlex :: Reg -> String
printRegAlex = render . prt 0

-- you may want to change render and parenth

render :: [String] -> String
render = rend (0::Int) where
  rend i ss = case ss of
    "["      :ts -> cons "["  $ rend i ts
    "("      :ts -> cons "("  $ rend i ts
    t  : "," :ts -> cons t    $ space "," $ rend i ts
    t  : ")" :ts -> cons t    $ cons ")"  $ rend i ts
    t  : "]" :ts -> cons t    $ cons "]"  $ rend i ts
    t        :ts -> space t   $ rend i ts
    _            -> ""
  cons s t  = s ++ t
  new i s   = s
  space t s = if null s then t else t ++ " " ++ s

parenth :: [String] -> [String]
parenth ss = ["("] ++ ss ++ [")"]

-- the printer class does the job
class Print a where
  prt :: Int -> a -> [String]
  prtList :: [a] -> [String]
  prtList = concat . map (prt 0)

instance Print a => Print [a] where
  prt _ = prtList

instance Print Char where
  prt _ c = if isAlphaNum c then [[c]] else ['^':[c]]
  prtList s = map (concat . prt 0) s

prPrec :: Int -> Int -> [String] -> [String]
prPrec i j = if j<i then parenth else id

instance Print Ident where
  prt _ (Ident i) = [i]

instance Print Reg where
  prt i e = case e of
   RSeq reg0 reg -> prPrec i 2 (concat [prt 2 reg0 , prt 3 reg])
   RAlt reg0 reg -> prPrec i 1 (concat [prt 1 reg0 , ["|"] , prt 2 reg])
   RMinus reg0 reg -> prPrec i 1 (concat [prt 2 reg0 , ["#"] , prt 2 reg])
   RStar reg -> prPrec i 3 (concat [prt 3 reg , ["*"]])
   RPlus reg -> prPrec i 3 (concat [prt 3 reg , ["+"]])
   ROpt reg  -> prPrec i 3 (concat [prt 3 reg , ["?"]])
   REps  -> prPrec i 3 (["$"])
   RChar c -> prPrec i 3 (concat [prt 0 c])
   RAlts str -> prPrec i 3 (concat [["["],prt 0 str,["]"]])
   RSeqs str -> prPrec i 2 (concat (map (prt 0) str))
   RDigit  -> prPrec i 3 (concat [["^d"]])
   RLetter  -> prPrec i 3 (concat [["^l"]])
   RUpper  -> prPrec i 3 (concat [["^c"]])
   RLower  -> prPrec i 3 (concat [["^s"]])
   RAny  -> prPrec i 3 (concat [["^u"]])