Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
Synopsis
- newtype Parser s r = Parser ([s] -> ([(r, [s])], DifferenceList (ParseError [s])))
- anySymbol :: Parser s s
- satisfy :: (s -> Bool) -> Parser s s
- empty :: Alternative f => f a
- failp :: Parser s a
- succeed :: a -> Parser s a
- pure :: Applicative f => a -> f a
- (<|>) :: Alternative f => f a -> f a -> f a
- (<<|>) :: Parser s a -> Parser s a -> Parser s a
- (<*>) :: Applicative f => f (a -> b) -> f a -> f b
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- (>>=) :: Monad m => m a -> (a -> m b) -> m b
- look :: Parser s [s]
- parseAndTrace :: (ErrorsPretty s, Ord s) => Config -> Parser s a -> [s] -> [(a, [s])]
- parseWithConfig :: Ord s => Config -> Parser s a -> [s] -> Either (ParseErrorBundle [s]) (NonEmpty (a, [s]))
- parse :: (ErrorsPretty s, Ord s) => Parser s a -> [s] -> [(a, [s])]
The type of parsers
An input string is mapped to a list of successful parses.
For each succesful parse, we return the result of type r
,
and the remaining input string. The input must be a list of
symbols.
Parser ([s] -> ([(r, [s])], DifferenceList (ParseError [s]))) |
Elementary parsers
satisfy :: (s -> Bool) -> Parser s s Source #
Takes a predicate and returns a parser that parses a single symbol satisfying that predicate.
empty :: Alternative f => f a #
The identity of <|>
pure :: Applicative f => a -> f a #
Lift a value.
Parser combinators
(<|>) :: Alternative f => f a -> f a -> f a infixl 3 #
An associative binary operation
(<<|>) :: Parser s a -> Parser s a -> Parser s a infixr 3 Source #
Biased choice. If the left hand side parser succeeds, the right hand side is not considered. Use with care!
(<*>) :: Applicative f => f (a -> b) -> f a -> f b infixl 4 #
Sequential application.
A few functors support an implementation of <*>
that is more
efficient than the default one.
Example
Used in combination with (
, <$>
)(
can be used to build a record.<*>
)
>>>
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 <$> produceFoo <*> produceBar <*> produceBaz
(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 #
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, <$>
is function
application lifted over a Functor
.
Examples
Convert from a
to a Maybe
Int
using Maybe
String
show
:
>>>
show <$> Nothing
Nothing>>>
show <$> Just 3
Just "3"
Convert from an
to an
Either
Int
Int
Either
Int
String
using show
:
>>>
show <$> Left 17
Left 17>>>
show <$> Right 17
Right "17"
Double each element of a list:
>>>
(*2) <$> [1,2,3]
[2,4,6]
Apply even
to the second element of a pair:
>>>
even <$> (2,2)
(2,True)
(>>=) :: Monad m => m a -> (a -> m b) -> m b infixl 1 #
Sequentially compose two actions, passing any value produced by the first as an argument to the second.
'as
' can be understood as the >>=
bsdo
expression
do a <- as bs a
Lookahead
Running parsers
parseAndTrace :: (ErrorsPretty s, Ord s) => Config -> Parser s a -> [s] -> [(a, [s])] Source #
Runs a parser on a given string printing error messages to standard error (stderr).
The ErrorsPretty
constraint is automatically fulfilled by Show
instances. But if you see the following GHC error, you usually need to
add an (
constraint to your function and ErrorsPretty
s)import
ParseLib.Error (
.ErrorsPretty
)
Overlapping instances for ErrorsPretty s arising from a use of ‘parseAndTrace’
ErrorsPretty
is not defined in this package but in
uu-tc-error-error
. We
did this so you can switch back and forth between this library and
uu-tc
without the need to
remove ErrorsPretty
constraints from your code. Just permanently keep
uu-tc-error-error
in your .cabal
file. It does not conflict with
uu-tc
because there are
no module name collisions.
parseWithConfig :: Ord s => Config -> Parser s a -> [s] -> Either (ParseErrorBundle [s]) (NonEmpty (a, [s])) Source #
Runs a parser on a given string. Pretty print the error information
with errorBundlePrettyImproved
.
parse :: (ErrorsPretty s, Ord s) => Parser s a -> [s] -> [(a, [s])] Source #
Runs a parser on a given string printing error messages to standard error (stderr).
Notice that, when using parse
, you might need to add Ord
and
ErrorsPretty
constraints to your own functions and ensure your own
data types are deriving (
.Ord
, Show
)
The ErrorsPretty
constraint is automatically fulfilled by Show
instances. But if you see the following GHC error, you usually need to
add an (
constraint to your function and ErrorsPretty
s)import
ParseLib.Error (
.ErrorsPretty
)
Overlapping instances for ErrorsPretty s arising from a use of ‘parse’
ErrorsPretty
is not defined in this package but in
uu-tc-error-error
. We
did this so you can switch back and forth between this library and
uu-tc
without the need to
remove ErrorsPretty
constraints from your code. Just permanently keep
uu-tc-error-error
in your .cabal
file. It does not conflict with
uu-tc
because there are
no module name collisions.