/*
*******************************************************************************
* Copyright (C) 1996-2009, International Business Machines Corporation and *
* others. All Rights Reserved. *
*******************************************************************************
*/
package com.ibm.icu.text;
import java.util.Hashtable;
/**
* RuleBasedTransliterator
is a transliterator
* that reads a set of rules in order to determine how to perform
* translations. Rule sets are stored in resource bundles indexed by
* name. Rules within a rule set are separated by semicolons (';').
* To include a literal semicolon, prefix it with a backslash ('\').
* Whitespace, as defined by UCharacterProperty.isRuleWhiteSpace()
,
* is ignored. If the first non-blank character on a line is '#',
* the entire line is ignored as a comment.
Each set of rules consists of two groups, one forward, and one * reverse. This is a convention that is not enforced; rules for one * direction may be omitted, with the result that translations in * that direction will not modify the source text. In addition, * bidirectional forward-reverse rules may be specified for * symmetrical transformations.
* *Rule syntax
* *Rule statements take one of the following forms:
* *$alefmadda=\u0622;
$alefmadda
", will be replaced by
* the Unicode character U+0622. Variable names must begin
* with a letter and consist only of letters, digits, and
* underscores. Case is significant. Duplicate names cause
* an exception to be thrown, that is, variables cannot be
* redefined. The right hand side may contain well-formed
* text of any length, including no text at all ("$empty=;
").
* The right hand side may contain embedded UnicodeSet
* patterns, for example, "$softvowel=[eiyEIY]
".ai>$alefmadda;
ai<$alefmadda;
ai<>$alefmadda;
Translation rules consist of a match pattern and an output
* string. The match pattern consists of literal characters,
* optionally preceded by context, and optionally followed by
* context. Context characters, like literal pattern characters,
* must be matched in the text being transliterated. However, unlike
* literal pattern characters, they are not replaced by the output
* text. For example, the pattern "abc{def}
"
* indicates the characters "def
" must be
* preceded by "abc
" for a successful match.
* If there is a successful match, "def
" will
* be replaced, but not "abc
". The final '}
'
* is optional, so "abc{def
" is equivalent to
* "abc{def}
". Another example is "{123}456
"
* (or "123}456
") in which the literal
* pattern "123
" must be followed by "456
".
*
The output string of a forward or reverse rule consists of
* characters to replace the literal pattern characters. If the
* output string contains the character '|
', this is
* taken to indicate the location of the cursor after
* replacement. The cursor is the point in the text at which the
* next replacement, if any, will be applied. The cursor is usually
* placed within the replacement text; however, it can actually be
* placed into the precending or following context by using the
* special character '@
'. Examples:
** **
a {foo} z > | @ bar; # foo -> bar, move cursor * before a
* {foo} xyz > bar @@|; # foo -> bar, cursor between * y and z
UnicodeSet
* *UnicodeSet
patterns may appear anywhere that
* makes sense. They may appear in variable definitions.
* Contrariwise, UnicodeSet
patterns may themselves
* contain variable references, such as "$a=[a-z];$not_a=[^$a]
",
* or "$range=a-z;$ll=[$range]
".
UnicodeSet
patterns may also be embedded directly
* into rule strings. Thus, the following two rules are equivalent:
** **
$vowel=[aeiou]; $vowel>'*'; # One way to do this
* [aeiou]>'*'; * # * Another way
See {@link UnicodeSet} for more documentation and examples.
* *Segments
* *Segments of the input string can be matched and copied to the * output string. This makes certain sets of rules simpler and more * general, and makes reordering possible. For example:
* *** **
([a-z]) > $1 $1; * # * double lowercase letters
* ([:Lu:]) ([:Ll:]) > $2 $1; # reverse order of Lu-Ll pairs
The segment of the input string to be copied is delimited by
* "(
" and ")
". Up to
* nine segments may be defined. Segments may not overlap. In the
* output string, "$1
" through "$9
"
* represent the input string segments, in left-to-right order of
* definition.
Anchors
* *Patterns can be anchored to the beginning or the end of the text. This is done with the
* special characters '^
' and '$
'. For example:
** **
^ a > 'BEG_A'; # match 'a' at start of text
* a > 'A'; # match other instances * of 'a'
* z $ > 'END_Z'; # match 'z' at end of text
* z > 'Z'; # match other instances * of 'z'
It is also possible to match the beginning or the end of the text using a UnicodeSet
.
* This is done by including a virtual anchor character '$
' at the end of the
* set pattern. Although this is usually the match chafacter for the end anchor, the set will
* match either the beginning or the end of the text, depending on its placement. For
* example:
** **
$x = [a-z$]; # match 'a' through 'z' OR anchor
* $x 1 > 2; # match '1' after a-z or at the start
* 3 $x > 4; # match '3' before a-z or at the end
Example
* *The following example rules illustrate many of the features of * the rule language.
* *Rule 1. | *abc{def}>x|y |
*
Rule 2. | *xyz>r |
*
Rule 3. | *yz>q |
*
Applying these rules to the string "adefabcdefz
"
* yields the following results:
|adefabcdefz |
* Initial state, no rules match. Advance * cursor. | *
a|defabcdefz |
* Still no match. Rule 1 does not match * because the preceding context is not present. | *
ad|efabcdefz |
* Still no match. Keep advancing until * there is a match... | *
ade|fabcdefz |
* ... | *
adef|abcdefz |
* ... | *
adefa|bcdefz |
* ... | *
adefab|cdefz |
* ... | *
adefabc|defz |
* Rule 1 matches; replace "def "
* with "xy " and back up the cursor
* to before the 'y '. |
*
adefabcx|yz |
* Although "xyz " is
* present, rule 2 does not match because the cursor is
* before the 'y ', not before the 'x '.
* Rule 3 does match. Replace "yz "
* with "q ". |
*
adefabcxq| |
* The cursor is at the end; * transliteration is complete. | *
The order of rules is significant. If multiple rules may match * at some point, the first matching rule is applied.
* *Forward and reverse rules may have an empty output string. * Otherwise, an empty left or right hand side of any statement is a * syntax error.
* *Single quotes are used to quote any character other than a
* digit or letter. To specify a single quote itself, inside or
* outside of quotes, use two single quotes in a row. For example,
* the rule "'>'>o''clock
" changes the
* string ">
" to the string "o'clock
".
*
Notes
* *While a RuleBasedTransliterator is being built, it checks that * the rules are added in proper order. For example, if the rule * "a>x" is followed by the rule "ab>y", * then the second rule will throw an exception. The reason is that * the second rule can never be triggered, since the first rule * always matches anything it matches. In other words, the first * rule masks the second rule.
* *Copyright (c) IBM Corporation 1999-2000. All rights reserved.
* * @author Alan Liu * @internal * @deprecated This API is ICU internal only. */ public class RuleBasedTransliterator extends Transliterator { private Data data; /** * Constructs a new transliterator from the given rules. * @param rules rules, separated by ';' * @param direction either FORWARD or REVERSE. * @exception IllegalArgumentException if rules are malformed * or direction is invalid. * @internal * @deprecated This API is ICU internal only. */ /*public RuleBasedTransliterator(String ID, String rules, int direction, UnicodeFilter filter) { super(ID, filter); if (direction != FORWARD && direction != REVERSE) { throw new IllegalArgumentException("Invalid direction"); } TransliteratorParser parser = new TransliteratorParser(); parser.parse(rules, direction); if (parser.idBlockVector.size() != 0 || parser.compoundFilter != null) { throw new IllegalArgumentException("::ID blocks illegal in RuleBasedTransliterator constructor"); } data = (Data)parser.dataVector.get(0); setMaximumContextLength(data.ruleSet.getMaximumContextLength()); }*/ /** * Constructs a new transliterator from the given rules in the *FORWARD
direction.
* @param rules rules, separated by ';'
* @exception IllegalArgumentException if rules are malformed
* or direction is invalid.
* @internal
* @deprecated This API is ICU internal only.
*/
/*public RuleBasedTransliterator(String ID, String rules) {
this(ID, rules, FORWARD, null);
}*/
RuleBasedTransliterator(String ID, Data data, UnicodeFilter filter) {
super(ID, filter);
this.data = data;
setMaximumContextLength(data.ruleSet.getMaximumContextLength());
}
/**
* Implements {@link Transliterator#handleTransliterate}.
* @internal
* @deprecated This API is ICU internal only.
*/
protected synchronized void handleTransliterate(Replaceable text,
Position index, boolean incremental) {
/* We keep start and limit fixed the entire time,
* relative to the text -- limit may move numerically if text is
* inserted or removed. The cursor moves from start to limit, with
* replacements happening under it.
*
* Example: rules 1. ab>x|y
* 2. yc>z
*
* |eabcd start - no match, advance cursor
* e|abcd match rule 1 - change text & adjust cursor
* ex|ycd match rule 2 - change text & adjust cursor
* exz|d no match, advance cursor
* exzd| done
*/
/* A rule like
* a>b|a
* creates an infinite loop. To prevent that, we put an arbitrary
* limit on the number of iterations that we take, one that is
* high enough that any reasonable rules are ok, but low enough to
* prevent a server from hanging. The limit is 16 times the
* number of characters n, unless n is so large that 16n exceeds a
* uint32_t.
*/
int loopCount = 0;
int loopLimit = (index.limit - index.start) << 4;
if (loopLimit < 0) {
loopLimit = 0x7FFFFFFF;
}
while (index.start < index.limit &&
loopCount <= loopLimit &&
data.ruleSet.transliterate(text, index, incremental)) {
++loopCount;
}
}
static class Data {
public Data() {
variableNames = new Hashtable