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GHC 9.10.3 · lts/ghc-9.10.x · 248f8f0 · 2026-10-05

Moduleregex-base-0.94.0.3Haskell2010

Text.Regex.Base.RegexLike

Classes and instances for Regex matching.

All the classes are declared here, and some common type aliases, and the MatchResult data type.

The only instances here are for Extract String, Extract ByteString, and Extract Text. There are no data values. The RegexContext instances are in Text.Regex.Base.Context, except for ones which run afoul of a repeated variable (RegexContext regex a a), which are defined in each modules' String and ByteString modules.

  • 9 types
  • 5 classes

Type aliases

4 declarations
typetype MatchOffset = Int
#

0 based index from start of source, or (-1) for unused

Data types

1 declaration

Classes

9 declarations
classclass RegexOptions regex compOpt execOpt | regex -> compOpt execOpt, compOpt -> regex execOpt, execOpt -> regex compOpt where
#

Rather than carry them around separately, the options for how to execute a regex are kept as part of the regex. There are two types of options. Those that can only be specified at compilation time and never changed are compOpt. Those that can be changed later and affect how matching is performed are execOpt. The actually types for these depend on the backend.

Methods

  • blankCompOpt :: compOpt

    No options set at all in the backend.

  • blankExecOpt :: execOpt

    No options set at all in the backend.

  • defaultCompOpt :: compOpt

    Reasonable options (extended, caseSensitive, multiline regex).

  • defaultExecOpt :: execOpt

    Reasonable options (extended, caseSensitive, multiline regex).

  • setExecOpts :: execOpt -> regex -> regex

    Forget old flags and use new ones.

  • getExecOpts :: regex -> execOpt

    Retrieve the current flags.

classclass RegexOptions regex compOpt execOpt => RegexMaker regex compOpt execOpt source | regex -> compOpt execOpt, compOpt -> regex execOpt, execOpt -> regex compOpt where
#

RegexMaker captures the creation of the compiled regular expression from a source type and an option type. Methods makeRegexM and makeRegexM report parse errors using MonadError, usually (Either String regex).

The makeRegex function has a default implementation that depends on makeRegexOpts and uses defaultCompOpt and defaultExecOpt. Similarly for makeRegexM and makeRegexOptsM.

There are also default implementations for makeRegexOpts and makeRegexOptsM in terms of each other. So a minimal instance definition needs to only define one of these, hopefully makeRegexOptsM.

Methods

classclass Extract source => RegexLike regex source where
#

RegexLike is parametrized on a regular expression type and a source type to run the matching on.

There are default implementations: matchTest and matchOnceText use matchOnce; matchCount and matchAllText use matchAll. Conversely, matchOnce uses matchOnceText and matchAll uses matchAllText. So a minimal complete instance need to provide at least (matchOnce or matchOnceText) and (matchAll or matchAllText). Additional definitions are often provided where they will increase efficiency.

[ c | let notVowel = makeRegex "[^aeiou]" :: Regex, c <- ['a'..'z'], matchTest notVowel [c]  ]

"bcdfghjklmnpqrstvwxyz"

The strictness of these functions is instance dependent.

Methods

  • matchOnce :: regex -> source -> Maybe MatchArray

    This returns the first match in the source (it checks the whole source, not just at the start). This returns an array of (offset,length) index pairs for the match and captured substrings. The offset is 0-based. A (-1) for an offset means a failure to match. The lower bound of the array is 0, and the 0th element is the (offset,length) for the whole match.

  • matchAll :: regex -> source -> [MatchArray]

    matchAll returns a list of matches. The matches are in order and do not overlap. If any match succeeds but has 0 length then this will be the last match in the list.

  • matchCount :: regex -> source -> Int

    matchCount returns the number of non-overlapping matches returned by matchAll.

  • matchTest :: regex -> source -> Bool

    matchTest returns True if there is a match somewhere in the source (it checks the whole source not just at the start).

  • matchAllText :: regex -> source -> [MatchText source]

    This is matchAll with the actual subsections of the source instead of just the (offset,length) information.

  • matchOnceText :: regex -> source -> Maybe (source, MatchText source, source)

    This can return a tuple of three items: the source before the match, an array of the match and captured substrings (with their indices), and the source after the match.

classclass RegexLike regex source => RegexContext regex source target where
#

RegexContext is the polymorphic interface to do matching. Since target is polymorphic you may need to supply the type explicitly in contexts where it cannot be inferred.

The monadic matchM version uses fail to report when the regex has no match in source. Two examples:

Here the contest Bool is inferred:

[ c | let notVowel = makeRegex "[^aeiou]" :: Regex, c <- ['a'..'z'], match notVowel [c]  ]

"bcdfghjklmnpqrstvwxyz"

Here the context [String] must be supplied:

let notVowel = (makeRegex "[^aeiou]" :: Regex )
in do { c <- ['a'..'z'] ; matchM notVowel [c] } :: [String]

["b","c","d","f","g","h","j","k","l","m","n","p","q","r","s","t","v","w","x","y","z"]

Methods

Instances26RegexContext, …
classclass Extract source where
#

Extract allows for indexing operations on String or ByteString.

Methods

  • before :: Int -> source -> source

    before is a renamed take.

  • after :: Int -> source -> source

    after is a renamed drop.

  • empty :: source

    When there is no match, this can construct an empty data value.

  • extract :: (Int, Int) -> source -> source

    extract takes an offset and length, and has this default implementation:

      extract (off, len) source = before len (after off source)
Instances6Extract
  • Extract ByteStringDefined in regex-base-0.94.0.3 · Text.Regex.Base.RegexLike
  • Extract ByteStringDefined in regex-base-0.94.0.3 · Text.Regex.Base.RegexLike
  • Extract StringDefined in regex-base-0.94.0.3 · Text.Regex.Base.RegexLike
  • Extract TextDefined in regex-base-0.94.0.3 · Text.Regex.Base.RegexLike
  • Extract TextDefined in regex-base-0.94.0.3 · Text.Regex.Base.RegexLike
  • Extract (Seq a)Defined in regex-base-0.94.0.3 · Text.Regex.Base.RegexLike
newtypenewtype AllTextSubmatches (f :: Type -> Type) b
#

Used in results of RegexContext instances.

Constructors

Instances4RegexContext
newtypenewtype AllMatches (f :: Type -> Type) b
#

Used in results of RegexContext instances.

Constructors

Instances3RegexContext
newtypenewtype AllTextMatches (f :: Type -> Type) b
#

Used in results of RegexContext instances.

Constructors

Instances6RegexContext