Question

（noob alert）我正在经历Write yourself a Scheme in 48 hours;但是在编译与Ch.4，错误检查和异常有关的代码时，我得到一个“不在范围内：ParseError”消息（按照教程1：1，不需要在这里重复）。我使用GHC 7.6.3。导入部分：

import Control.Monad
import Text.ParserCombinators.Parsec hiding (spaces)

但我也尝试添加import Text.ParserCombinators.Parsec.Error和import Text.Parsec.Error，但无济于事。似乎ParseError ADT由几个不同的库公开，但由于某种原因，编译器没有看到它。其他Parsec功能可以正常工作。

任何指针？提前谢谢

Answer 1

修复来自于替换一个函数声明中的变量名：

WRONG：

showError :: LispError -> String
showError (UnboundVar msg varname) = msg ++ ": " ++ varname
showError (BadSpecialForm msg frm) = msg ++ ": " ++ show frm
showError (NotFunction msg f) = msg ++ ": " ++ show f
showError (NumArgs expected found) = "Expected " ++ show expected ++ " args: found values     " ++ unwordsList found
showError (TypeMismatch expected found) = "Invalid type: expected " ++ expected ++ ", found " ++ show found
showError (ParseError pe) = "Parse error at " ++ show pe

RIGHT：

showError :: LispError -> String
showError (UnboundVar message varname) = message ++ ": " ++ varname
showError (BadSpecialForm message form) = message ++ ": " ++ show form
showError (NotFunction message func) = message ++ ": " ++ show func
showError (NumArgs expected found) = "Expected " ++ show expected 
                              ++ " args: found values " ++ unwordsList found
showError (TypeMismatch expected found) = "Invalid type: expected " ++ expected
                                   ++ ", found " ++ show found
showError (Parser parseErr) = "Parse error at " ++ show parseErr

我发誓，我不明白。任何澄清都将受到高度赞赏。

ParseError不在范围内 - “48小时内的方案”

1 个答案: