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Signature REG_EXP (pkg github.com/diku-dk/sml-regexp)

NFA implementation of regular expression matching. 

structure RegExp : REG_EXP (pkg github.com/diku-dk/sml-regexp)

signature REG_EXP =
  sig
    type regexp
    val fromString : string -> regexp
    val match      : regexp -> string -> bool
    val extract    : regexp -> string -> string list option
  end
[type regexp]
is the type of regular expressions.

[fromString s]
returns a regular expression by parsing the string s according to the syntax given for regular expressions below. Raises (Fail msg) in case s is not a regular expression according to the syntax below.

[match r s]
returns true if the regular expression r matches the string s according to the description below. Returns false if the regular expression r does not match the string s.

[extract r s]
returns NONE if the regular expression r does not match the string s. Returns SOME l if the regular expression r matches the string s; the list l is a list of all substrings in s that is matched by some regular expression appearing in parentheses in r. Strings in l appear in the same order as they appear in s. Nested parentheses are supported, but empty substrings of s that are matched by a regular expression appearing in a parenthesis in r are not listed in l. Grammar for regular expressions (RegExp): 
   re ::= re1 "|" re2         re1 or re2
       |  re1 re2             re1 followed by re2
       |  re "*"              re repeated zero or more times
       |  re "+"              re repeated one or more times
       |  re "?"              re zero or one time
       |  "(" re ")"          re
       |  c                   specific character
       |  "\" c               escaped character; c is one of |,*,+,?,(,),[,],$,.,\,t,n,v,f,r
       |  "[" class "]"       character class
       |  "[^" class "]"      negated character class
       |  $                   empty string
       |  .                   any character

   class ::=  c               specific character
          |   "\" c           escaped character; c is one of [,],-,\,t,n,v,f,r
          |   c1 "-" c2       ascii character range
          |                   empty class
          |   class class     composition
Whitespace is significant. Special characters can be escaped by \. Authors: Ken Friis Larsen. Support for regular expression classes and parenthesis extraction by Martin Elsman.

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