use parser combinators to parse the shell commands. simplified CommandLine type

src-3.0/PGF/ExprSyntax.hs

@@ -0,0 +1,71 @@
+module PGF.ExprSyntax(readExp, showExp,
+                      pExp,ppExp,
+                      
+                     -- helpers
+                      pIdent
+                     ) where
+
+import PGF.CId
+import PGF.Data
+
+import Data.Char
+import Control.Monad
+import qualified Text.PrettyPrint as PP
+import qualified Text.ParserCombinators.ReadP as RP
+
+
+-- | parses 'String' as an expression
+readExp :: String -> Maybe Exp
+readExp s = case [x | (x,cs) <- RP.readP_to_S (pExp False) s, all isSpace cs] of
+              [x] -> Just x
+              _   -> Nothing
+
+-- | renders expression as 'String'
+showExp :: Exp -> String
+showExp = PP.render . ppExp False
+
+pExps :: RP.ReadP [Exp]
+pExps = liftM2 (:) (pExp True) pExps RP.<++ (RP.skipSpaces >> return [])
+
+pExp :: Bool -> RP.ReadP Exp
+pExp isNested = RP.skipSpaces >> (pParen RP.<++ pAbs RP.<++ pApp RP.<++ pNum RP.<++ pStr RP.<++ pMeta)
+  where 
+        pParen = RP.between (RP.char '(') (RP.char ')') (pExp False)
+        pAbs = do xs <- RP.between (RP.char '\\') (RP.skipSpaces >> RP.string "->") (RP.sepBy1 (RP.skipSpaces >> pCId) (RP.skipSpaces >> RP.char ','))
+                  t  <- pExp False
+                  return (EAbs xs t)
+        pApp = do f  <- pCId
+                  ts <- (if isNested then return [] else pExps)
+                  return (EApp f ts)
+        pMeta = do RP.char '?'
+                   x <- RP.munch1 isDigit
+                   return (EMeta (read x))
+        pStr = RP.char '"' >> liftM EStr (RP.manyTill (pEsc RP.<++ RP.get) (RP.char '"'))
+          where
+            pEsc = RP.char '\\' >> RP.get    
+        pNum = do x <- RP.munch1 isDigit
+                  ((RP.char '.' >> RP.munch1 isDigit >>= \y -> return (EFloat (read (x++"."++y))))
+                   RP.<++
+                   (return (EInt (read x))))
+
+pCId = fmap mkCId pIdent
+
+pIdent = liftM2 (:) (RP.satisfy isIdentFirst) (RP.munch isIdentRest)
+  where
+    isIdentFirst c = c == '_' || isLetter c
+    isIdentRest c = c == '_' || c == '\'' || isAlphaNum c
+
+ppExp isNested (EAbs xs t) = ppParens isNested (PP.char '\\' PP.<>
+                                                PP.hsep (PP.punctuate PP.comma (map (PP.text . prCId) xs)) PP.<+>
+                                                PP.text "->" PP.<+>
+                                                ppExp False t)
+ppExp isNested (EApp f []) = PP.text (prCId f)
+ppExp isNested (EApp f ts) = ppParens isNested (PP.text (prCId f) PP.<+> PP.hsep (map (ppExp True) ts))
+ppExp isNested (EStr   s)  = PP.text (show s)
+ppExp isNested (EInt   n)  = PP.integer n
+ppExp isNested (EFloat d)  = PP.double d
+ppExp isNested (EMeta  n)  = PP.char '?' PP.<> PP.int n
+ppExp isNested (EVar  id)  = PP.text (prCId id)
+
+ppParens True  = PP.parens
+ppParens False = id