Normalizer
Related Doc:
package impl
Expand the wildcards (\".\") and character classes, transforming them into disjunctions over the supplied alphabet
Regular expressions can have character classes and wildcards. In order to produce a NFA, they should be expanded to disjunctions. In the case of wildcards or negated characted classes, the complete alphabet must also be known to produce the expansion:
Example transformations with alphabet: abcdefgh
[abc] -> a|b|c [abc] -> d|e|f|g|h def[abc] -> def(d|e|f|g|h) . -> a|b|c|d|e|f|g|h abc. -> abc(a|b|c|d|e|f|g|h)
As the alphabet can be potentially huge (such as unicode is) something must be done to reduce the number of disjunctions:
[abc] -> a|b|c [abc] -> <other_char> def[abc] -> def(d|e|f|<other_char>) . -> <other_char> abc. -> abc(a|b|c|<other_char>)
Where <other_char> is a special metacharacter that matches any of the characters of the alphabet not present in the regex. Note that with this technique knowing the whole alphabet explicitly is not needed.
Care must be taken when the regex is meant to be used for an operation with another regex (such as intersection or difference). In this case, <other_char> must match only the characters present in neither regex. Example:
Regex space: [abc] and [cd] Characters present in any regex: abcd [abc] -> a|b|c [cd] -> a|b|<other_char>