haskell - Haskell パーセク接頭辞演算子の問題

Question

GHC を使用して Windows でコンパイルします。これが私のコードです（こちらからも入手できます）：

module GMC.GMLParser (parseGML) where

import Control.Applicative ((<$>), (<*>))
import Text.ParserCombinators.Parsec
import Text.ParserCombinators.Parsec.Expr
import Text.ParserCombinators.Parsec.Language
import qualified Text.ParserCombinators.Parsec.Token as P

type VarIdent = String
type FunIdent = String

data Expr =
      Var VarIdent
    | IntLit Integer
    | StringLit String
    | BiLit Bool
    | Op String Expr Expr
    | UnOp String Expr
    | Call FunIdent [Expr]
    deriving (Eq, Show)

data Stat =
      Seq [Stat]
    | Skip
    | Assign (Maybe VarIdent) Expr
    | If Expr Stat (Maybe Stat)
    deriving (Eq, Show)

lexer = P.makeTokenParser gmlDef

parens          = P.parens lexer    
braces          = P.braces lexer    
semi            = P.semi lexer
semiSep         = P.semiSep lexer  
semiSep1        = P.semiSep1 lexer    
commaSep        = P.commaSep lexer
commaSep1       = P.commaSep1 lexer
brackets        = P.brackets lexer
whiteSpace      = P.whiteSpace lexer    
symbol          = P.symbol lexer    
identifier      = P.identifier lexer    
reserved        = P.reserved lexer    
reservedOp      = P.reservedOp lexer
integer         = P.integer lexer    
charLiteral     = P.charLiteral lexer    
stringLiteral   = P.stringLiteral lexer


operators =
    [ [ prefix "-" ]
    , [ op "*"  AssocLeft, op "/"  AssocLeft ]
    , [ op "+"  AssocLeft, op "-"  AssocLeft ]
    , [ op "=" AssocNone, op "<>" AssocNone, op "<="  AssocNone
      , op "<" AssocNone, op ">="  AssocNone, op ">" AssocNone ]
    , [ op "&" AssocRight, op "&&" AssocRight ] -- Right for shortcircuiting
    , [ op "|" AssocRight, op "||" AssocRight ] -- Right for shortcircuiting
    , [ op ":=" AssocRight ]
    ]
    where
      op name assoc   = Infix (do{ reservedOp name
                                  ; return (\x y -> Op name x y) 
                                  }) assoc
      prefix name     = Prefix  (do{ reservedOp name
                                  ; return (\x -> UnOp name x)
                                  })


gmlDef :: LanguageDef st
gmlDef = emptyDef
    { commentStart    = "/*"
    , commentEnd      = "*/"
    , commentLine     = "//"
    , nestedComments  = True
    , identStart      = letter
    , identLetter     = alphaNum <|> oneOf "_"
    , reservedNames   = []
    , reservedOpNames = []
    , caseSensitive   = True
    }

parseGML :: String -> Either ParseError [Stat]
parseGML input = parse (whiteSpace >> many stat) "" input

intLit :: Parser Expr
intLit = IntLit <$> integer

strLit :: Parser Expr
strLit = StringLit <$> stringLiteral

variable :: Parser Expr
variable = do ident <- identifier
              memb <- optional $ symbol "." -- ignored for now, only parse its existance
              vname <- optional identifier -- ignored for now, only parse its existance
              indx <- optional $ brackets expr -- ignored for now, only parse its existance
              return (Var ident)

expr :: Parser Expr
expr = buildExpressionParser operators genExpr

genExpr :: Parser Expr
genExpr = choice [ intLit
                 , strLit
                 , try callExpr
                 , variable
                 , parens expr
                 ]

callExpr :: Parser Expr
callExpr = Call <$> identifier <*> parens (commaSep expr)

stat :: Parser Stat
stat =  do optional $ skipMany1 semi
           choice [ ifStat
                  , assignStat
                  , seqStat
                  ]

seqStat :: Parser Stat
seqStat = do stmts <- braces $ many stat
             return $ if null stmts then Skip else Seq stmts

ifStat :: Parser Stat
ifStat = If <$> (reserved "if" >> expr)
            <*> (optional (reserved "then") >> stat)
            <*> (optionMaybe $ reserved "else" >> stat)

assignStat :: Parser Stat
assignStat = do ident <- (optionMaybe $ try $ variable >> symbol "=")
                stmt <- case ident of
                    Just x -> expr
                    Nothing -> callExpr
                return (Assign ident stmt)

問題は、プレフィックス付きの実数と変数を解析すると奇妙な結果が生じることです。

x=-3[Assign (Just "=") (UnOp "-" (IntLit 3))]どちらが正しいかを示します。x=5+-3ただし、 andのようなより複雑な式でx = (arr[4]>-1 && 1)は、正しくない結果が得られるようです。

x = arr[4]>-1しかし、与える[Assign (Just '=') (Var "arr")]べきです[Assign (Just "x") (Op ">" (Var "arr") (UnOp "-" (IntLit 1)))]

x=5+-3奇妙なこと[Assign (Just "=" (IntLit 5))に、あるべきときに与えます[Assign (Just "x") (Op "+" (IntLit 5) (UnOp "-" (IntLit 3)))]

-演算子の優先順位に関係があるため、または一般的に前置演算子の実装が信頼できないように思われるためだと思います。ご指導いただければ幸いです。

ありがとう！