regex-applicative-0.3.4: Regex-based parsing with applicative interface

Copyright(c) Roman Cheplyaka
LicenseMIT
MaintainerRoman Cheplyaka <roma@ro-che.info>
Stabilityexperimental
Safe HaskellSafe
LanguageHaskell2010

Text.Regex.Applicative

Contents

Description

To get started, see some examples on the wiki: https://github.com/feuerbach/regex-applicative/wiki/Examples

Synopsis

Documentation

data RE s a Source #

Type of regular expressions that recognize symbols of type s and produce a result of type a.

Regular expressions can be built using Functor, Applicative, Alternative, and Filtrable instances in the following natural way:

  • f <$> ra matches iff ra matches, and its return value is the result of applying f to the return value of ra.
  • pure x matches the empty string (i.e. it does not consume any symbols), and its return value is x
  • rf <*> ra matches a string iff it is a concatenation of two strings: one matched by rf and the other matched by ra. The return value is f a, where f and a are the return values of rf and ra respectively.
  • ra <|> rb matches a string which is accepted by either ra or rb. It is left-biased, so if both can match, the result of ra is used.
  • empty is a regular expression which does not match any string.
  • many ra matches concatenation of zero or more strings matched by ra and returns the list of ra's return values on those strings.
  • some ra matches concatenation of one or more strings matched by ra and returns the list of ra's return values on those strings.
  • catMaybes ram matches iff ram matches and produces 'Just _'.
  • ra <> rb matches ra followed by rb. The return value is a <> b, where a and b are the return values of ra and rb respectively. (See https://github.com/feuerbach/regex-applicative/issues/37#issue-499781703 for an example usage.)
  • mempty matches the empty string (i.e. it does not consume any symbols), and its return value is the mempty value of type a.
Instances
Functor (RE s) Source # 
Instance details

Defined in Text.Regex.Applicative.Types

Methods

fmap :: (a -> b) -> RE s a -> RE s b #

(<$) :: a -> RE s b -> RE s a #

Applicative (RE s) Source # 
Instance details

Defined in Text.Regex.Applicative.Types

Methods

pure :: a -> RE s a #

(<*>) :: RE s (a -> b) -> RE s a -> RE s b #

liftA2 :: (a -> b -> c) -> RE s a -> RE s b -> RE s c #

(*>) :: RE s a -> RE s b -> RE s b #

(<*) :: RE s a -> RE s b -> RE s a #

Alternative (RE s) Source # 
Instance details

Defined in Text.Regex.Applicative.Types

Methods

empty :: RE s a #

(<|>) :: RE s a -> RE s a -> RE s a #

some :: RE s a -> RE s [a] #

many :: RE s a -> RE s [a] #

Filtrable (RE s) Source #

Since: 0.3.4

Instance details

Defined in Text.Regex.Applicative.Types

Methods

mapMaybe :: (a -> Maybe b) -> RE s a -> RE s b #

catMaybes :: RE s (Maybe a) -> RE s a #

filter :: (a -> Bool) -> RE s a -> RE s a #

mapMaybeA :: (Traversable (RE s), Applicative p) => (a -> p (Maybe b)) -> RE s a -> p (RE s b) #

filterA :: (Traversable (RE s), Applicative p) => (a -> p Bool) -> RE s a -> p (RE s a) #

mapEither :: (a -> Either b c) -> RE s a -> (RE s b, RE s c) #

mapEitherA :: (Traversable (RE s), Applicative p) => (a -> p (Either b c)) -> RE s a -> p (RE s b, RE s c) #

partitionEithers :: RE s (Either a b) -> (RE s a, RE s b) #

(char ~ Char, string ~ String) => IsString (RE char string) Source # 
Instance details

Defined in Text.Regex.Applicative.Types

Methods

fromString :: String -> RE char string #

Semigroup a => Semigroup (RE s a) Source #

Since: 0.3.4

Instance details

Defined in Text.Regex.Applicative.Types

Methods

(<>) :: RE s a -> RE s a -> RE s a #

sconcat :: NonEmpty (RE s a) -> RE s a #

stimes :: Integral b => b -> RE s a -> RE s a #

Monoid a => Monoid (RE s a) Source #

Since: 0.3.4

Instance details

Defined in Text.Regex.Applicative.Types

Methods

mempty :: RE s a #

mappend :: RE s a -> RE s a -> RE s a #

mconcat :: [RE s a] -> RE s a #

sym :: Eq s => s -> RE s s Source #

Match and return the given symbol

psym :: (s -> Bool) -> RE s s Source #

Match and return a single symbol which satisfies the predicate

msym :: (s -> Maybe a) -> RE s a Source #

Like psym, but allows to return a computed value instead of the original symbol

anySym :: RE s s Source #

Match and return any single symbol

string :: Eq a => [a] -> RE a [a] Source #

Match and return the given sequence of symbols.

Note that there is an IsString instance for regular expression, so if you enable the OverloadedStrings language extension, you can write string "foo" simply as "foo".

Example:

{-# LANGUAGE OverloadedStrings #-}
import Text.Regex.Applicative

number = "one" *> pure 1  <|>  "two" *> pure 2

main = print $ "two" =~ number

reFoldl :: Greediness -> (b -> a -> b) -> b -> RE s a -> RE s b Source #

Match zero or more instances of the given expression, which are combined using the given folding function.

Greediness argument controls whether this regular expression should match as many as possible (Greedy) or as few as possible (NonGreedy) instances of the underlying expression.

data Greediness Source #

Constructors

Greedy 
NonGreedy 

few :: RE s a -> RE s [a] Source #

Match zero or more instances of the given expression, but as few of them as possible (i.e. non-greedily). A greedy equivalent of few is many.

Examples:

Text.Regex.Applicative> findFirstPrefix (few anySym  <* "b") "ababab"
Just ("a","abab")
Text.Regex.Applicative> findFirstPrefix (many anySym  <* "b") "ababab"
Just ("ababa","")

comap :: (s2 -> s1) -> RE s1 a -> RE s2 a Source #

RE is a profunctor. This is its contravariant map.

(A dependency on the profunctors package doesn't seem justified.)

withMatched :: RE s a -> RE s (a, [s]) Source #

Return matched symbols as part of the return value

match :: RE s a -> [s] -> Maybe a Source #

Attempt to match a string of symbols against the regular expression. Note that the whole string (not just some part of it) should be matched.

Examples:

Text.Regex.Applicative> match (sym 'a' <|> sym 'b') "a"
Just 'a'
Text.Regex.Applicative> match (sym 'a' <|> sym 'b') "ab"
Nothing

(=~) :: [s] -> RE s a -> Maybe a infix 2 Source #

s =~ a = match a s

replace :: RE s [s] -> [s] -> [s] Source #

Replace matches of the regular expression with its value.

Text.Regex.Applicative > replace ("!" <$ sym 'f' <* some (sym 'o')) "quuxfoofooooofoobarfobar"
"quux!!!bar!bar"

findFirstPrefix :: RE s a -> [s] -> Maybe (a, [s]) Source #

Find a string prefix which is matched by the regular expression.

Of all matching prefixes, pick one using left bias (prefer the left part of <|> to the right part) and greediness.

This is the match which a backtracking engine (such as Perl's one) would find first.

If match is found, the rest of the input is also returned.

See also findFirstPrefixWithUncons, of which this is a special case.

Examples:

Text.Regex.Applicative> findFirstPrefix ("a" <|> "ab") "abc"
Just ("a","bc")
Text.Regex.Applicative> findFirstPrefix ("ab" <|> "a") "abc"
Just ("ab","c")
Text.Regex.Applicative> findFirstPrefix "bc" "abc"
Nothing

findLongestPrefix :: RE s a -> [s] -> Maybe (a, [s]) Source #

Find the longest string prefix which is matched by the regular expression.

Submatches are still determined using left bias and greediness, so this is different from POSIX semantics.

If match is found, the rest of the input is also returned.

See also findLongestPrefixWithUncons, of which this is a special case.

Examples:

Text.Regex.Applicative Data.Char> let keyword = "if"
Text.Regex.Applicative Data.Char> let identifier = many $ psym isAlpha
Text.Regex.Applicative Data.Char> let lexeme = (Left <$> keyword) <|> (Right <$> identifier)
Text.Regex.Applicative Data.Char> findLongestPrefix lexeme "if foo"
Just (Left "if"," foo")
Text.Regex.Applicative Data.Char> findLongestPrefix lexeme "iffoo"
Just (Right "iffoo","")

findShortestPrefix :: RE s a -> [s] -> Maybe (a, [s]) Source #

Find the shortest prefix (analogous to findLongestPrefix)

See also findShortestPrefixWithUncons, of which this is a special case.

findFirstInfix :: RE s a -> [s] -> Maybe ([s], a, [s]) Source #

Find the leftmost substring that is matched by the regular expression. Otherwise behaves like findFirstPrefix. Returns the result together with the prefix and suffix of the string surrounding the match.

findLongestInfix :: RE s a -> [s] -> Maybe ([s], a, [s]) Source #

Find the leftmost substring that is matched by the regular expression. Otherwise behaves like findLongestPrefix. Returns the result together with the prefix and suffix of the string surrounding the match.

findShortestInfix :: RE s a -> [s] -> Maybe ([s], a, [s]) Source #

Find the leftmost substring that is matched by the regular expression. Otherwise behaves like findShortestPrefix. Returns the result together with the prefix and suffix of the string surrounding the match.

Custom uncons function

The following functions take an argument that splits the input into the first symbol and the remaining input (if the input is non-empty).

It is useful, for example, for feeding a Text to a regex matcher:

>>> findFirstPrefixWithUncons Text.uncons (many (sym 'a')) "aaa"
Just ("aaa", "")

For another example, feeding input symbols annotated with source positions into a matcher, preserving the positions in the remaining input so the location of a lexical error can be recovered:

data AList a b = AList { annotation :: a, stripAnnotation :: Maybe (b, AList a b) }

findLongestPrefixAnnotated :: RE s a -> AList b s -> Maybe (a, AList b s)
fondLongestPrefixAnnotated = findLongestPrefixWithUncons stripAnnotation

The use of the other functions taking an uncons argument is exactly analogous.

findFirstPrefixWithUncons :: (ss -> Maybe (s, ss)) -> RE s a -> ss -> Maybe (a, ss) Source #

Find the first prefix, with the given uncons function.

Since: 0.3.4

findLongestPrefixWithUncons :: (ss -> Maybe (s, ss)) -> RE s a -> ss -> Maybe (a, ss) Source #

Find the longest prefix, with the given uncons function.

Since: 0.3.4

findShortestPrefixWithUncons :: (ss -> Maybe (s, ss)) -> RE s a -> ss -> Maybe (a, ss) Source #

Find the shortest prefix (analogous to findLongestPrefix), with the given uncons function.

Since: 0.3.4