// Convert to an obligatory rewrite transducer
public static Fst ToRewriter(this Fst fst, ISet <char> alphabet)
{
var all = FsaBuilder.All(alphabet);
var notInDomain = all
.Difference(all.Concat(fst.Domain()).Concat(all))
.Identity()
.Optional();
return(notInDomain.Concat(fst.Concat(notInDomain).Star()));
}
public void AllFsaTest()
{
var fsa = FsaBuilder.All(new HashSet <char> {
'a', 'b', 'c'
});
Assert.Equal(3, fsa.States.Count);
Assert.Equal(1, fsa.Initial.Count);
Assert.Equal(2, fsa.Final.Count);
Assert.False(fsa.Recognize("d"));
Assert.False(fsa.Recognize("ad"));
Assert.True(new[] { "ab", string.Empty, "abc", "bbbac", "cba", "cbcbbcaaaaacb" }.All(fsa.Recognize));
}
public void ComplexFsaConstructionTest2()
{
// .*@.*\.com
var all = FsaBuilder.All(
Enumerable.Range(97, 27).Select(Convert.ToChar).ToHashSet());
var fsa = all
.Concat(
FsaBuilder.FromWord("@"),
all,
FsaBuilder.FromWord(".com"))
.Determinize();
Assert.DoesNotContain(new[] { "*****@*****.**", "you@@gmail.com", "*****@*****.**", "*****@*****.**" }, fsa.Recognize);
Assert.True(new[] { "*****@*****.**", "*****@*****.**", "*****@*****.**" }.All(fsa.Recognize));
}
// Convert to an obligatory leftmost-longest match rewrite transducer (Karttunen 1996)
public static Fst ToLmlRewriter(this Fst fst, ISet <char> alphabet)
{
if (alphabet.Intersect(markers).Any())
{
throw new ArgumentException("The alphabet contains invalid symbols.");
}
var alphabetStarFsa = FsaBuilder.All(alphabet).Minimal();
var allSymbols = alphabet.Concat(markers).ToHashSet();
var allSymbolsStarFsa = FsaBuilder.All(allSymbols).Minimal();
// Automaton recognizing all words that are not in the language of the input automaton (complement)
Fsa NotInLang(Fsa lang) => allSymbolsStarFsa.Difference(lang);
// Automaton recognizing all words that contain an occurrence of a word from the input automaton
Fsa ContainsLang(Fsa lang) => allSymbolsStarFsa.Concat(lang, allSymbolsStarFsa);
// All words w where each prefix of w representing a string in "P" is followed by a suffix which is in "S"
Fsa IfPThenS(Fsa p, Fsa s) => NotInLang(p.Concat(NotInLang(s)));
// All words for which each suffix from "S" is preceeded by a prefix from "P"
Fsa IfSThenP(Fsa p, Fsa s) => NotInLang(NotInLang(p).Concat(s));
Fsa PiffS(Fsa l, Fsa r) => IfPThenS(l, r).Intersect(IfSThenP(l, r));
/* Describes the words where every position is preceded by a string with a suffix in "L"
* if and only if it is followed by a string with a prefix in "R" */
Fsa LiffR(Fsa l, Fsa r) => PiffS(allSymbolsStarFsa.Concat(l), r.Concat(allSymbolsStarFsa));
var fstDomain = fst.Domain();
var initialMatch = // mark the beginnings of all rewrite occurrences by inserting "cb"
Intro(allSymbols, new HashSet <char> {
cb
})
.Compose(
LiffR(
FsaBuilder.FromSymbol(cb),
XIgnore(fstDomain, allSymbols, new HashSet <char> {
cb
}))
.Identity());
var leftToRight = // insert boundary markers ("lb", "rb") around the leftmost rewrite occurrences
alphabetStarFsa.Identity() // preceeded by arbitrary text that is not matched by the rule
.Concat(
FstBuilder.FromWordPair(cb.ToString(), lb.ToString()), // replace intial match marker with the left boundary marker
IgnoreX(fstDomain, allSymbols, new HashSet <char> {
cb
}).Identity(), // recognize matches with the leftover "cb" symbol inbetween the markers
FstBuilder.FromWordPair(string.Empty, rb.ToString())) // insert right boundary marker at the end of the matched substring
.Star() // handle multiple rewrite occurrences
.Concat(alphabetStarFsa.Identity()) // succeeded by arbitrary text that is not matched by the rule
.Compose(
FstBuilder.FromWordPair(cb.ToString(), string.Empty).ToRewriter(allSymbols)); // delete the remaining initial match markers
var includesNotLongestMatches =
ContainsLang(
FsaBuilder.FromSymbol(lb)
.Concat(
IgnoreX(fstDomain, allSymbols, new HashSet <char> {
lb, rb
})
.Intersect(ContainsLang(FsaBuilder.FromSymbol(rb)))));
// amongst occurrences with the same starting point, preserve only the longest ones
var longestMatch = NotInLang(includesNotLongestMatches).Identity();
var replacement = // replace the rewrite occurrence and delete the left and right markers
FstBuilder.FromWordPair(lb.ToString(), string.Empty) // delete the left boundary marker
.Concat(
fst, // perform the replacement
FstBuilder.FromWordPair(rb.ToString(), string.Empty)) // delete the right boundary marker
.ToRewriter(allSymbols);
return(initialMatch.Compose(leftToRight, longestMatch, replacement));
}
// Convert an FST to an optional rewrite transducer
public static Fst ToOptionalRewriter(this Fst fst, ISet <char> alphabet)
{
var idAll = FsaBuilder.All(alphabet).Identity();
return(idAll.Concat(fst.Concat(idAll).Star()));
}