New parser for Hatt with support for associativity and operator precedence

hatt-parser2.hs

module Data.Logic.Propositional.Parser2 where

import Data.Logic.Propositional

import Text.Parsec.Prim ((<|>), (<?>), runPT)
import Text.Parsec.Char (char, letter, spaces, string)
import Text.Parsec.Expr

parseExpr' = runPT expr ()

expr = buildExpressionParser operators term
    <?> "compound expression"

term =  parens expr
    <|> variable
    <?> "expression"

variable = do c <- letter
              return $ Variable (Var c)
        <?> "variable"

parens p = do char '('
              spaces
              x <- p
              spaces
              char ')'
              return x
        <?> "parens"

operators = [ [Prefix (string "~" >> return Negation)]
            , [binary "&" Conjunction]
            , [binary "|" Disjunction]
            , [binary "->" Conditional]
            , [binary "<->" Biconditional]
            ]

binary n c = Infix (spaces >> string n >> spaces >> return c) AssocRight