hxt-7.5: A collection of tools for processing XML with Haskell.ContentsIndex
Text.XML.HXT.Validator.RE
Description

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.

Version : $Id: RE.hs,v 1.1 20040902 19:12:03 hxml Exp $

Synopsis
data RE a
= RE_ZERO String
| RE_UNIT
| RE_SYM a
| RE_DOT
| RE_REP RE a
| RE_PLUS RE a
| RE_OPT RE a
| RE_SEQ RE a RE a
| RE_ALT RE a RE a
re_unit :: RE a
re_zero :: String -> RE a
re_sym :: a -> RE a
re_rep :: RE a -> RE a
re_plus :: RE a -> RE a
re_opt :: RE a -> RE a
re_seq :: RE a -> RE a -> RE a
re_alt :: RE a -> RE a -> RE a
re_dot :: RE a
checkRE :: Show a => RE a -> String
matches :: (Eq a, Show a) => RE a -> [a] -> RE a
nullable :: Show a => RE a -> Bool
printRE :: Show a => RE a -> String
Documentation
data RE a
Data type for regular expressions.
Constructors
RE_ZERO String
RE_UNIT
RE_SYM a
RE_DOT
RE_REP RE a
RE_PLUS RE a
RE_OPT RE a
RE_SEQ RE a RE a
RE_ALT RE a RE a
show/hide Instances
Eq a => Eq (RE a)
Show a => Show (RE a)
re_unit :: RE a

Constructs a regular expression for an empty sequence.

  • returns : regular expression for an empty sequence
re_zero :: String -> RE a

Constructs a regular expression for an empty set.

  • 1.parameter errMsg : error message
  • returns : regular expression for an empty set
re_sym :: a -> RE a

Constructs a regular expression for accepting a symbol

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

Constructs an optional repetition (*) of a regular expression

  • 1.parameter re_a : regular expression to be repeted
  • returns : new regular expression
re_plus :: RE a -> RE a

Constructs a repetition (+) of a regular expression

  • 1.parameter re_a : regular expression to be repeted
  • returns : new regular expression
re_opt :: RE a -> RE a

Constructs an option (?) of a regular expression

  • 1.parameter re_a : regular expression to be optional
  • returns : new regular expression
re_seq :: RE a -> RE a -> RE a

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
re_alt :: RE a -> RE a -> RE a

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
re_dot :: RE a

Constructs a regular expression for accepting any singel symbol

  • returns : regular expression for accepting any singel symbol
checkRE :: Show a => RE a -> String

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
matches :: (Eq a, Show a) => RE a -> [a] -> RE a

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
nullable :: Show a => RE a -> Bool

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
printRE :: Show a => RE a -> String

Constructs a string representation of a regular expression.

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