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module Parser (parseProgram) where
import Control.Monad
import Data.Char
import Data.List (foldl')
import Text.Parsec hiding (token)
import AST
type Parser = Parsec String ()
parseProgram :: String -> String -> Either ParseError [Definition]
parseProgram fname source = parse pProgram fname source
pProgram :: Parser [Definition]
pProgram = do
whitespaceTo0
choice
[eof >> return []
,(:) <$> pDef <*> pProgram]
-- | Assumes column 0
pDef :: Parser Definition
pDef = do
name <- pName
whitespace
token ":"
whitespace
typ <- pTerm 0
whitespaceTo0
name2 <- pName
when (name /= name2) $
fail $ "Definition of '" ++ name ++ "' followed by definition for '" ++ name2 ++ "'"
whitespace
token "="
whitespace
rhs <- pTerm 0
return (Definition name (rhs :| typ))
-- operator precedences:
-- 0 _:_
-- 1 (_ : _) -> _
-- 2 _,_
pTerm :: Int -> Parser Term
pTerm p | p <= 0 = do
e1 <- pTerm 1
whitespace
choice
[do token ":"
whitespace
e2 <- pTerm 1
return (TAnnot (e1 :| e2))
,return e1]
pTerm 1 = do
e1 <- pTerm 2
whitespace
choice
[do (token "->" <|> token "→")
(x :| ty) <- case e1 of
TAnnot (TVar x :| ty) -> return (x :| ty)
_ -> fail $ "Expected (x : type) as left-hand side of (->)"
whitespace
e2 <- pTerm 1
return (TPi x ty e2)
,return e1]
pTerm 2 = do
e1 <- pTerm 3
whitespace
choice
[do token ","
whitespace
e2 <- pTerm 2
return (TPair e1 e2)
,return e1]
pTerm _ = pTermEAtom
pTermEAtom :: Parser Term
pTermEAtom = pLambda <|> pSpecialApp <|> pApp
pLambda :: Parser Term
pLambda = do
void (char '\\') <|> token "λ"
whitespace
_ <- char '('
whitespace
x <- pName
whitespace
token ":"
whitespace
ty <- pTerm 0
whitespace
_ <- char ')'
whitespace
token "->"
whitespace
rhs <- pTerm 0
return (TLam x ty rhs)
pSpecialApp :: Parser Term
pSpecialApp = pSet <|> pSetw <|> pSigma
where
pSet :: Parser Term
pSet = do
token "Set"
whitespace
e <- pTermEAtom
return (TSet e)
pSetw :: Parser Term
pSetw = do
token "Setw"
whitespace
n <- read <$> many1 digit
return (TSetw n)
pSigma :: Parser Term
pSigma = do
token "Sigma"
whitespace
_ <- char '('
whitespace
x <- pName
whitespace
token ":"
whitespace
ty <- pTerm 0
whitespace
_ <- char ')'
whitespace
rhs <- pTermEAtom
return (TSigma x ty rhs)
pApp :: Parser Term
pApp = do
e1 <- pAtom
args <- many (try (whitespace >> pAtom))
return (foldl' TApp e1 args)
pAtom :: Parser Term
pAtom = choice
[do _ <- char '('
whitespace
e <- pTerm 0
whitespace
_ <- char ')'
return e
,TVar <$> pName]
-- TODO TPair, TSigma ("%"). The rest are environment entries.
pName :: Parser Name
pName = do
name <- many1 pNameChar
guard (name `notElem` keywords)
guard (head name /= '\\') -- lambda syntax
return name
where
keywords = ["=", "->", "→", ":", "?", "\\", "λ", "∀", "..", "..."
,"forall", "data", "import", "in", "let"
,"Sigma", "," -- temporary
]
pNameChar :: Parser Char
pNameChar = satisfy (\c -> not (isSpace c) && c `notElem` ".;{}()@\"")
inlineWhite :: Parser ()
inlineWhite = do
skipMany inlineSpace
choice
[inlineComment
-- TODO: nested {- -} comments
,return ()]
inlineComment :: Parser ()
inlineComment = token "--" >> manyTill anyChar (lookAhead newline) >> return ()
-- | Skips to the furthest point from here that can be reached without
-- consuming any tokens, and without ending on column 0.
whitespace :: Parser ()
whitespace = do
inlineWhite
optional $ try $
many newline >> (inlineSpace <|> inlineComment) >> whitespace
inlineSpace :: Parser ()
inlineSpace = void (satisfy (\c -> isSpace c && c /= '\n')) <?> "inline whitespace"
-- | Skips as much whitespace as possible, and throws an error if that doesn't
-- leave us on column 0.
whitespaceTo0 :: Parser ()
whitespaceTo0 = do
inlineWhite
choice
[eof
,newline >> whitespaceTo0
,do pos <- getPosition
when (sourceColumn pos /= 1) $
unexpected "indented code"]
token :: String -> Parser ()
token s = try $ string s >> (eof <|> void (lookAhead (satisfy (\c -> isSpace c || c `elem` ".;{}()@\""))))
|
