Documentation

Parser synonym for String.

An infix synonym for fmap.

The name of this operator is an allusion to $. Note the similarities between their types:

 ($)  ::              (a -> b) ->   a ->   b
(<$>) :: Functor f => (a -> b) -> f a -> f b

Whereas $ is function application, <$> is function application lifted over a Functor.

Examples

>>> show <$> Nothing
Nothing
>>> show <$> Just 3
Just "3"

>>> show <$> Left 17
Left 17
>>> show <$> Right 17
Right "17"

>>> (*2) <$> [1,2,3]
[2,4,6]

>>> even <$> (2,2)
(2,True)

The parser try p behaves like parser p, except that it pretends that it hasn't consumed any input when an error occurs.

Sequential application.

A few functors support an implementation of <*> that is more efficient than the default one.

Example

>>> data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}

>>> produceFoo :: Applicative f => f Foo

>>> produceBar :: Applicative f => f Bar
>>> produceBaz :: Applicative f => f Baz

>>> mkState :: Applicative f => f MyState
>>> mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz

Lift a value.

Sequence actions, discarding the value of the first argument.

Examples

>>> Just 2 *> Just 3
Just 3

>>> Nothing *> Just 3
Nothing

>>> import Data.Char
>>> import Text.ParserCombinators.ReadP
>>> let p = string "my name is " *> munch1 isAlpha <* eof
>>> readP_to_S p "my name is Simon"
[("Simon","")]

Sequence actions, discarding the value of the second argument.

An associative binary operation

One or more.

Zero or more.

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

Examples

>>> 'a' <$ Just 2
Just 'a'
>>> 'a' <$ Nothing
Nothing

A variant of <*> with the types of the arguments reversed. It differs from flip (<*>) in that the effects are resolved in the order the arguments are presented.

Examples

>>> (<**>) (print 1) (id <$ print 2)
1
2

>>> flip (<*>) (print 1) (id <$ print 2)
2
1

The parser satisfy f succeeds for any character for which the supplied function f returns True. Returns the character that is actually parsed.

char c parses a single character c. Returns the parsed character.

string s parses a sequence of characters given by s. Returns the parsed string

choice ps tries to apply the parsers in the list ps in order, until one of them succeeds. Returns the value of the succeeding parser.

option x p tries to apply parser p. If p fails without consuming input, it returns the value x, otherwise the value returned by p.

skipMany p applies the parser p zero or more times, skipping its result.

sepBy1 p sep parses one or more occurrences of p, separated by sep. Returns a list of values returned by p.

manyTill p end applies parser p zero or more times until parser end succeeds. Returns the list of values returned by p.

Parses a white space character (any character which satisfies isSpace) Returns the parsed character.

The class for parser input.

Run a parser.

This parser succeeds for any character. Returns the parsed character.

oneOf cs succeeds if the current character is in the supplied list of characters cs. Returns the parsed character.

As the dual of oneOf, noneOf cs succeeds if the current character not in the supplied list of characters cs. Returns the parsed character.

Parses a letter or digit (a character between '0' and '9'). Returns the parsed character.

Parses a digit. Returns the parsed character.

Parses a hexadecimal digit (a digit or a letter between 'a' and 'f' or 'A' and 'F'). Returns the parsed character.

skipSome p applies the parser p one or more times, skipping its result.