| Safe Haskell | None |
|---|---|
| Language | Haskell98 |
Text.Regex.TDFA
Description
The Text.Regex.TDFA module provides a backend for regular expressions. It provides instances for the classes defined and documented in Text.Regex.Base and re-exported by this module. If you import this along with other backends then you should do so with qualified imports (with renaming for convenience).
This regex-tdfa package implements, correctly, POSIX extended regular expressions. It is highly unlikely that the regex-posix package on your operating system is correct, see http://www.haskell.org/haskellwiki/Regex_Posix for examples of your OS's bugs.
Importing and using
Add to your package.yaml/cabal file:
dependencies: - regex-tdfa
In modules where you need to use regexes:
import Text.Regex.TDFA
Note that regex-tdfa does not provide support for Text by default.
If you need this functionality, add regex-tdfa-text
as a dependency and import Text.Regex.TDFA.Text ().
Basics
λ> let emailRegex = "[a-zA-Z0-9+._-]+@[a-zA-Z-]+\\.[a-z]+" λ> "my email is email@email.com"=~emailRegex :: Bool >>> True -- non-monadic λ> <to-match-against>=~<regex> -- monadic, usesfailon lack of match λ> <to-match-against>=~~<regex>
(=~) and (=~~) are polymorphic in their return type. This is so that
regex-tdfa can pick the most efficient way to give you your result based on
what you need. For instance, if all you want is to check whether the regex
matched or not, there's no need to allocate a result string. If you only want
the first match, rather than all the matches, then the matching engine can stop
after finding a single hit.
This does mean, though, that you may sometimes have to explicitly specify the type you want, especially if you're trying things out at the REPL.
Common use cases
Get the first match
-- returns empty string if no match a=~b :: String -- or ByteString, or Text... λ> "alexis-de-tocqueville"=~"[a-z]+" :: String >>> "alexis" λ> "alexis-de-tocqueville"=~"[0-9]+" :: String >>> ""
Check if it matched at all
a=~b :: Bool λ> "alexis-de-tocqueville"=~"[a-z]+" :: Bool >>> True
Get first match + text before/after
-- if no match, will just return whole -- string in the first element of the tuple a =~ b :: (String, String, String) λ> "alexis-de-tocqueville"=~"de" :: (String, String, String) >>> ("alexis-", "de", "-tocqueville") λ> "alexis-de-tocqueville"=~"kant" :: (String, String, String) >>> ("alexis-de-tocqueville", "", "")
Get first match + submatches
-- same as above, but also returns a list of just submatches. -- submatch list is empty if regex doesn't match at all a=~b :: (String, String, String, [String]) λ> "div[attr=1234]"=~"div\\[([a-z]+)=([^]]+)\\]" :: (String, String, String, [String]) >>> ("", "div[attr=1234]", "", ["attr","1234"])
Get all matches
-- can also return Data.Array instead of ListgetAllTextMatches(a=~b) :: [String] λ>getAllTextMatches("john anne yifan"=~"[a-z]+") :: [String] >>> ["john","anne","yifan"]
Feature support
This package does provide captured parenthesized subexpressions.
Depending on the text being searched this package supports Unicode.
The [Char] and (Seq Char) text types support Unicode. The ByteString
and ByteString.Lazy text types only support ASCII. It is possible to
support utf8 encoded ByteString.Lazy by using regex-tdfa and
regex-tdfa-utf8
packages together (required the utf8-string package).
As of version 1.1.1 the following GNU extensions are recognized, all anchors:
- \` at beginning of entire text
- \' at end of entire text
- \< at beginning of word
- \> at end of word
- \b at either beginning or end of word
- \B at neither beginning nor end of word
The above are controlled by the newSyntax Bool in CompOption.
Where the "word" boundaries means between characters that are and are not in the [:word:] character class which contains [a-zA-Z0-9_]. Note that \< and \b may match before the entire text and \> and \b may match at the end of the entire text.
There is no locale support, so collating elements like [.ch.] are simply ignored and equivalence classes like [=a=] are converted to just [a]. The character classes like [:alnum:] are supported over ASCII only, valid classes are alnum, digit, punct, alpha, graph, space, blank, lower, upper, cntrl, print, xdigit, word.
This package does not provide "basic" regular expressions. This package does not provide back references inside regular expressions.
The package does not provide Perl style regular expressions. Please look at the regex-pcre and pcre-light packages instead.
This package does not provide find-and-replace.
Avoiding backslashes
If you find yourself writing a lot of regexes, take a look at raw-strings-qq. It'll let you write regexes without needing to escape all your backslashes.
{-# LANGUAGE QuasiQuotes #-}
import Text.RawString.QQ
import Text.Regex.TDFA
λ> "2 * (3 + 1) / 4" =~ [r|\([^)]+\)|] :: String
>>> "(3 + 1)"
Synopsis
- getVersion_Text_Regex_TDFA :: Version
- (=~) :: (RegexMaker Regex CompOption ExecOption source, RegexContext Regex source1 target) => source1 -> source -> target
- (=~~) :: (RegexMaker Regex CompOption ExecOption source, RegexContext Regex source1 target, MonadFail m) => source1 -> source -> m target
- data Regex
- data ExecOption = ExecOption {}
- data CompOption = CompOption {
- caseSensitive :: Bool
- multiline :: Bool
- rightAssoc :: Bool
- newSyntax :: Bool
- lastStarGreedy :: Bool
- module Text.Regex.Base
Documentation
(=~) :: (RegexMaker Regex CompOption ExecOption source, RegexContext Regex source1 target) => source1 -> source -> target Source #
This is the pure functional matching operator. If the target
cannot be produced then some empty result will be returned. If
there is an error in processing, then error will be called.
(=~~) :: (RegexMaker Regex CompOption ExecOption source, RegexContext Regex source1 target, MonadFail m) => source1 -> source -> m target Source #
This is the monadic matching operator. If a single match fails,
then fail will be called.
The TDFA backend specific Regex type, used by this module's RegexOptions and RegexMaker
Instances
data ExecOption Source #
Constructors
| ExecOption | |
Fields
| |
Instances
data CompOption Source #
Control whether the pattern is multiline or case-sensitive like Text.Regex and whether to capture the subgroups (\1, \2, etc). Controls enabling extra anchor syntax.
Constructors
| CompOption | |
Fields
| |
Instances
module Text.Regex.Base