diff --git a/Parser/Fix/Simple.hs b/Parser/Fix/Simple.hs new file mode 100644 --- /dev/null +++ b/Parser/Fix/Simple.hs @@ -0,0 +1,77 @@ +{-| Simple fix-expression parser + + If in doubt, just use parsefix +-} + +module Parser.Fix.Simple (TokenType (..), Fixity (..), parsefix, foldfix, shunt) where + +import Control.Monad; +import Control.Monad.Instances; +import Data.List; +import Data.Maybe; + +-- | Fixity/Associativity +data Fixity = Prefix | InfixLeft | InfixRight | InfixNull | Postfix deriving Eq; + +data TokenType = -- | Plain, i.e. operand + TokenPlain + | TokenLParenth + | TokenRParenth + -- | Operator, with fixity and precedence + | TokenOper Fixity Integer + deriving Eq; + +-- | Shunt and Fold +parsefix :: (t -> a, t -> t -> a, t -> t -> t -> a) -> (t -> TokenType) -> [t] -> [a]; +parsefix apply = liftM2 (.) (foldfix apply) shunt; + +-- | Fold expression in postfix form +foldfix :: (t -> a, t -> t -> a, t -> t -> t -> a) -> (t -> TokenType) -> [t] -> [a]; +foldfix (apply0, apply1, apply2) lookup_t = + let { + foldfix' _ [] = []; + foldfix' stack (t:ts) = + case lookup_t t of { + TokenPlain -> foldfix' (t:stack) ts; + TokenOper fix p | fix_arity fix == 2, + (x:y:stack') <- stack -> apply2 t x y : foldfix' stack' ts + | fix_arity fix == 1, + (x:stack') <- stack -> apply1 t x : foldfix' stack' ts + | otherwise -> error "Malformed fix expression"; + TokenLParenth -> error "Mismatched Parentheses"; + TokenRParenth -> error "Mismatched Parentheses"; + }; + + fix_arity Prefix = 1; + fix_arity Postfix = 1; + fix_arity InfixLeft = 2; + fix_arity InfixRight = 2; + fix_arity InfixNull = 2; + } in foldfix' []; + +{-| Change from infix to postfix form + + Precedence at start is zero +-} +-- Dijkstra's algorithm +shunt :: (t -> TokenType) -> [t] -> [t]; +shunt lookup_t = join . snd . mapAccumR + (\ stack t -> + case lookup_t t of { + TokenPlain -> (stack, [t]); + TokenOper fix1 p1 | or $ map (== fix1) [InfixLeft, InfixRight, InfixNull] -> + case map lookup_t stack of { + (TokenOper fix2 p2 : _) | fix1 == InfixLeft && p1 <= p2 || + fix1 == InfixRight && p1 < p2 -> + (t : tail stack, [head stack]); + _ -> (t : id stack, []); + } + | Postfix == fix1 -> ( stack, [t]) + | Prefix == fix1 -> (t:stack, []) + ; + TokenLParenth -> (t:stack, []); + TokenRParenth -> case break ((== TokenLParenth) . lookup_t) stack of { + (ts, _:stack') -> (stack', ts); + (ts, _) -> (error "Mismatched Parentheses", ts); + }; + }) []; diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple; +main = defaultMain; diff --git a/fix-parser-simple.cabal b/fix-parser-simple.cabal new file mode 100644 --- /dev/null +++ b/fix-parser-simple.cabal @@ -0,0 +1,17 @@ +Name:fix-parser-simple +Version:15318.1 +Description:Simple fix-expression parser +License:LGPL +License-File:license.txt +Author:Matthew Farkas-Dyck +Maintainer:strake888@gmail.com +Category:Parser +Synopsis:Simple fix-expression parser +Build-Type:Simple +Cabal-Version: >= 1.2 + +Library { + Build-Depends: base >= 4 && < 5 + Extensions: PatternGuards + Exposed-Modules: Parser.Fix.Simple +} diff --git a/license.txt b/license.txt new file mode 100644 --- /dev/null +++ b/license.txt @@ -0,0 +1,165 @@ + GNU LESSER GENERAL PUBLIC LICENSE + Version 3, 29 June 2007 + + Copyright (C) 2007 Free Software Foundation, Inc. + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + + This version of the GNU Lesser General Public License incorporates +the terms and conditions of version 3 of the GNU General Public +License, supplemented by the additional permissions listed below. + + 0. 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