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

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

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

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. 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.

RegexContext is the polymorphic interface to do matching. Since target is polymorphic you may need to suply 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"]