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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
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