问题
I'm writing a monadic parser using Alex and Happy in Haskell.
My error function is defined like this:
parseError :: Token -> Alex a
parseError _ = alexError "error occurred"
How can I send custom errors (like incorrect type while trying to add a string to a number) during parsing?
UPDATE
The parser doesn't need to do the type checking, I'm doing it inside the production since I keep track of the operands type.
As said in a comment, I cannot use the parseError, so is there a way to print an error and stop the parser?
回答1:
I've solved it by implementing this function:
fatalError :: (Show a1, Show a) => [Char] -> a -> a1 -> t
fatalError s l c = error ("Error at line " ++ (show l) ++ " column " ++ (show c) ++ ": " ++ s)
and I call it from the production when an error is detected
来源：https://stackoverflow.com/questions/37059704/show-custom-errors-while-parsing-happy-haskell