A module for regular expression matching based on derivatives of regular expressions.

The code was taken from Joe English (http://www.flightlab.com/~joe/sgml/validate.html). Tested and extended by Martin Schmidt.

Further references for the algorithm:

Janusz A. Brzozowski.

Derivatives of Regular Expressions. Journal of the ACM, Volume 11, Issue 4, 1964.

Mark Hopkins.

Regular Expression Package. Posted to comp.compilers, 1994. Available per FTP at ftp://iecc.com/pub/file/regex.tar.gz.

Constructs a regular expression for an empty sequence.

• returns : regular expression for an empty sequence

Constructs a regular expression for an empty set.

• 1.parameter errMsg : error message
• returns : regular expression for an empty set

Constructs a regular expression for accepting a symbol

• 1.parameter sym : the symbol to be accepted
• returns : regular expression for accepting a symbol

Constructs an optional repetition (*) of a regular expression

• 1.parameter re_a : regular expression to be repeted
• returns : new regular expression

Constructs a repetition (+) of a regular expression

• 1.parameter re_a : regular expression to be repeted
• returns : new regular expression

Constructs an option (?) of a regular expression

• 1.parameter re_a : regular expression to be optional
• returns : new regular expression

Constructs a sequence (,) of two regular expressions

• 1.parameter re_a : first regular expression in sequence
• 2.parameter re_b : second regular expression in sequence
• returns : new regular expression

Constructs an alternative (|) of two regular expressions

• 1.parameter re_a : first regular expression of alternative
• 2.parameter re_b : second regular expression of alternative
• returns : new regular expression

Constructs a regular expression for accepting any singel symbol

• returns : regular expression for accepting any singel symbol

Checks if an input matched a regular expression. The function should be called after matches.

Was the sentence used in matches in the language of the regular expression? -> matches e s == s `in` L(e)?

• 1.parameter re : the derived regular expression
• returns : empty String if input matched the regular expression, otherwise an error message is returned

Derives a regular expression with respect to a sentence.

• 1.parameter re : regular expression
• 2.parameter s : sentence to which the regular expression is applied
• returns : the derived regular expression

Checks if a regular expression matches the empty sequence.

nullable e == [] `in` L(e)

This check indicates if a regular expression fits to a sentence or not.

• 1.parameter re : regular expression to be checked
• returns : true if regular expression matches the empty sequence, otherwise false

Constructs a string representation of a regular expression.

• 1.parameter re : a regular expression
• returns : the string representation of the regular expression