Haskell happy生成的源码有错误"parse error on input 'data'"

Question

我正在试用 Haskell 的快乐解析器生成器。在 happy.hs 中生成模块后（生成时没有问题！），我运行命令 ghc happy.hs，我得到错误：Line 297: parse error on input 'data'。有人有解决方案吗？或者告诉我在哪里可以获得解决方案？

我尝试在 GHCi 中加载模块，而不是使用 ghc 编译它。但它似乎也不起作用 - 我得到了同样的错误。

happy.y 中的代码（快乐来源）：

-- TODO: add more of my things!!!

{
    module Main where
}
%name calc
%tokentype { Token }
%error { parseError }
-- tokens
%token
    let { TokenLet }
    in { TokenIn }
    int { TokenInt $$ }
    var { TokenVar $$ }
    '=' { TokenEq }
    '+' { TokenPlus }
    '-' { TokenSub }
    '*' { TokenMul }
    '/' { TokenDvd }
    '(' { TokenOB }
    ')' { TokenCB }
%%
Exp : let var '=' Exp in Exp { Let    }
    | Exp1 { Exp1  }
Exp1 : Exp1 '+' Term { Plus   }
    | Exp1 '-' Term { Minus   }
    | Term { Term  }
Term : Term '*' Factor { Times   }
    | Term '/' Factor { Div   }
    | Factor { Factor  }
Factor : int { Int  }
    | var { Var  }
    | '(' Exp ')' { Brack  }

{
    parseError :: [Token] -> a
    parseError _ = error "Parse error! please try again..."

    data Exp = Let String Exp Exp
        | Exp1 Exp1
    deriving Show

    data Exp1 = Plus Exp1 Term
        | Minus Exp1 Term
        | Term Term
    deriving Show

    data Term = Times Term Factor
        | Div Term Factor
        | Factor Factor
    deriving Show

    data Factor = Int Int
        | Var String
        | Brack Exp
    deriving Show

    -- the tokens 
    data Token = TokenLet
        | TokenIn
        | TokenInt Int
        | TokenVar String
        | TokenEq
        | TokenPlus
        | TokenMinus
        | TokenTimes
        | TokenDiv
        | TokenOB
        | TokenCB
        deriving Show

    -- the lexer
    lexer :: String -> [Token]
    lexer [] = []
    lexer (c:cs)
        | isSpace c = lexer cs
        | isAlpha c = lexVar (c:cs)
        | isDigit c = lexNum (c:cs)
    lexer ('=':cs) = TokenEq : lexer cs
    lexer ('+':cs) = TokenPlus : lexer cs
    lexer ('-':cs) = TokenMinus : lexer cs
    lexer ('*':cs) = TokenTimes : lexer cs
    lexer ('/':cs) = TokenDiv : lexer cs
    lexer ('(':cs) = TokenOB : lexer cs
    lexer (')':cs) = TokenCB : lexer cs
    lexNum cs = TokenInt (read num) : lexer rest
    where (num,rest) = span isDigit cs
    lexVar cs =
        case span isAlpha cs of
        ("let",rest) -> TokenLet : lexer rest
        ("in",rest) -> TokenIn : lexer rest
        (var,rest) -> TokenVar var : lexer rest

    -- the main function
    main = getContents >>= print . calc . lexer
}

happy.hs和±10行出错的行（287~307行，包括）：

287: calc tks = happyRunIdentity happySomeParser where
288:  happySomeParser = happyThen (happyParse action_0 tks) (\x -> case x of 289: {HappyAbsSyn4 z -> happyReturn z; _other -> notHappyAtAll })
290: 
291: happySeq = happyDontSeq
292:
293:
294: parseError :: [Token] -> a
295:    parseError _ = error "Parse error! please try again..."
296:
297:    data Exp = Let String Exp Exp       -- <= I get error on this line!
298:       | Exp1 Exp1
299:    deriving Show
300:
301:    data Exp1 = Plus Exp1 Term
302:        | Minus Exp1 Term
303:        | Term Term
304:    deriving Show
305:
306:    data Term = Times Term Factor
307:        | Div Term Factor

我希望程序能够运行顺利而没有任何错误，但事实并非如此。

Answer 1

Happy 在文件的第 1 列生成其生成的代码。因此，要让您的代码被视为与生成的代码（您无法控制）相同的 module-where 块的一部分，它还必须位于文件的第 1 列。

从您的快乐文件中的 plain-Haskell 代码行的开头删除四个空格，您将进入下一个错误。删除空格时，请确保 deriving 子句和 where 子句从周围缩进一级。

Haskell happy生成的源码有错误"parse error on input 'data'"

Haskell source generated by happy has error "parse error on input 'data'"

haskell

parser-generator

alex