Safe Haskell | Safe |
---|---|

Language | Haskell2010 |

## Synopsis

- data RE s a
- data Greediness
- sym :: Eq s => s -> RE s s
- psym :: (s -> Bool) -> RE s s
- msym :: (s -> Maybe a) -> RE s a
- anySym :: RE s s
- few :: RE s a -> RE s [a]
- reFoldl :: Greediness -> (b -> a -> b) -> b -> RE s a -> RE s b
- withMatched :: RE s a -> RE s (a, [s])
- string :: Eq a => [a] -> RE a [a]
- digit :: Num a => RE Char a
- hexDigit :: Num a => RE Char a
- signed :: Num a => RE Char a -> RE Char a
- decimal :: Num a => RE Char a
- hexadecimal :: Num a => RE Char a
- match :: RE s a -> [s] -> Maybe a
- (=~) :: [s] -> RE s a -> Maybe a
- replace :: RE s [s] -> [s] -> [s]
- findFirstPrefix :: RE s a -> [s] -> Maybe (a, [s])
- findLongestPrefix :: RE s a -> [s] -> Maybe (a, [s])
- findShortestPrefix :: RE s a -> [s] -> Maybe (a, [s])
- findFirstInfix :: RE s a -> [s] -> Maybe ([s], a, [s])
- findLongestInfix :: RE s a -> [s] -> Maybe ([s], a, [s])
- findShortestInfix :: RE s a -> [s] -> Maybe ([s], a, [s])

# Regex

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`

and
`Alternative`

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.

data Greediness #

## Instances

# Building regular expressions

## Generic combinators

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

Like `psym`

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

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","")

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

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.

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

Return matched symbols as part of the return value

## Strings

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

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

## Digits

## Numbers

hexadecimal :: Num a => RE Char a #

Parse decimal number without sign.

# Running regular expressions

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

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

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

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]) #

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.

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]) #

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.

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]) #

Find the shortest prefix (analogous to `findLongestPrefix`

)

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

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]) #

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]) #

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.