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|
-----------------------------------------------------------------------------
--
-- (c) The GHC Team 1997-2000
--
-- Monad for the Haskell parser.
--
-----------------------------------------------------------------------------
-- Heavily modified to work with Frown, Ralf Hinze, 2001
> module HsParseMonad ( Token(..), Result(..), LexContext(..), P, Lex(..), unLex
> , runTokens, runHsModule
> , parseError, getSrcLoc, getContext, pushContext, popContext)
> where
>
> import HsSyn
> import Monad
> data Token
> = VarId String
> | QVarId (String,String)
> | ConId String
> | QConId (String,String)
> | VarSym String
> | ConSym String
> | QVarSym (String,String)
> | QConSym (String,String)
> | IntTok String
> | FloatTok String
> | Character Char
> | StringTok String
>
> -- Symbols
>
> | LeftParen
> | RightParen
> | SemiColon
> | LeftCurly
> | RightCurly
> | VRightCurly -- a virtual close brace
> | LeftSquare
> | RightSquare
> | Comma
> | Underscore
> | BackQuote
>
> -- Reserved operators
>
> | DotDot
> | DoubleColon
> | Equals
> | Backslash
> | Bar
> | LeftArrow
> | RightArrow
> | At
> | Tilde
> | DoubleArrow
> | Minus
> | Exclamation
>
> -- Reserved Ids
>
> | KW_As
> | KW_Case
> | KW_Class
> | KW_Data
> | KW_Default
> | KW_Deriving
> | KW_Do
> | KW_Else
> | KW_Hiding
> | KW_If
> | KW_Import
> | KW_In
> | KW_Infix
> | KW_InfixL
> | KW_InfixR
> | KW_Instance
> | KW_Let
> | KW_Module
> | KW_NewType
> | KW_Of
> | KW_Then
> | KW_Type
> | KW_Where
> | KW_Qualified
> | EOF
> deriving (Eq,Show)
A simple exception monad.
> data Result a = Fail String | Return a
> deriving (Show)
> instance Monad Result where
> Fail s >>= _k = Fail s
> Return a >>= k = k a
> return = Return
> fail = Fail
> instance MonadPlus Result where
> mzero = fail ""
> Fail _s `mplus` m = m
> Return a `mplus` _m = Return a
> data LexContext = NoLayout | Layout Int
> deriving (Eq, Ord, Show)
>
> type Contexts = [LexContext]
A state monad (in CPS style).
> type P a
> = String -- input string
> -> SrcLoc -- location of last token read
> -> Int -- current column
> -> Contexts -- layout information
> -> Result a
> {- non Haskell 98
> newtype Lex a = Lex (forall ans . (a -> P ans) -> P ans)
> unLex (Lex x) = x
> run :: Lex a -> P a
> run (Lex p) = p (\a -> \i l c s -> Return a)
> -}
> newtype Lex a = Lex ((a -> P Answer) -> P Answer)
> unLex (Lex x) = x
> data Answer = Tokens [Token] | HsModule' HsModule
>
> runTokens :: Lex [Token] -> P [Token]
> runTokens (Lex p) i l c s = p (\a -> \i l c s -> Return (Tokens a)) i l c s >>= \ (Tokens a) -> return a
>
> runHsModule :: Lex HsModule -> P HsModule
> runHsModule (Lex p) i l c s = p (\a -> \i l c s -> Return (HsModule' a)) i l c s >>= \ (HsModule' a) -> return a
> instance Monad Lex where
> return a = Lex (\ cont -> cont a)
> m >>= k = Lex (\ cont -> unLex m (\ a -> unLex (k a) cont))
> fail s = Lex (\ cont i l c stk -> fail s)
> parseError :: String -> Lex a
> parseError s = Lex (\ cont r (SrcLoc y x) c stk ->
> fail (show y ++ ":" ++ show x ++ ": " ++ s))
Accessing the state.
> getSrcLoc :: Lex SrcLoc
> getSrcLoc = Lex (\cont i l c s -> cont l i l c s)
> getContext :: Lex Contexts
> getContext = Lex (\cont i l c s -> cont s i l c s)
> pushContext :: LexContext -> Lex ()
> pushContext ctxt =
> Lex (\cont i l c s -> cont () i l c (ctxt:s))
> popContext :: Lex ()
> popContext =
> Lex (\ cont i l c stk ->
> case stk of
> [] -> error "Internal error: empty context in popContext"
> (_ : s) -> cont () i l c s)
|
