Parsing
Type instances
Application Parser instance:
Pure : takes a value and returns a parser that always succeeds with that value.
<*> : applies a function inside a parser to a value inside a parser.
Alternative Parser instance:
empty : represents a parser that always fails.
<|> : try the first parser and, if it fails, try the second parser.
Monad Parser instance
Pure : already define.
>>= : applies a parser to a value, then applies a function to the result.
Functions and Operators
(<?>) :: Parser a -> (Remaining -> ParseError) -> Parser a
Operator similar to <?> for custom error messages.
Add error message in stack error.
Utilization
Applicative Instance Examples:
pure
haskellCopy code-- Creating a parser that succeeds with the value 42
resultParser :: Parser Int
resultParser = pure 42
<*>
haskellCopy code-- Combining parsers to apply a function within a parser to a value within a parser
additionParser :: Parser Int
additionParser = (+) <$> parseNumber <*> parseNumber
Alternative Instance Examples:
empty
haskellCopy code-- Creating a parser that always fails
failParser :: Parser Int
failParser = empty
<|>
haskellCopy code-- Combining parsers to try one parser, and if it fails, try the second one
alternativeParser :: Parser Int
alternativeParser = successfulParser <|> failParser
Monad Instance Examples:
>>=
haskellCopy code-- Chaining parsers to apply a parser to a value, and then apply a function to the result
chainParser :: Parser Int
chainParser = parseNumber >>= \x -> parseNumber >>= \y -> return (x * y)
(<?>)
haskellCopy code-- Applying a custom error message in case of failure
customErrorParser :: Parser Int
customErrorParser = (parseNumber <?> CustomErrorFunction) >>= \x -> ...
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