builder := NewAhoCorasickBuilder(Opts{
  AsciiCaseInsensitive: true,
  MatchOnlyWholeWords:  true,
  MatchKind:            LeftMostLongestMatch,
  DFA:                  true,
})

ac := builder.Build([]string{"bear", "masha"})
haystack := "The Bear and Masha"
matches := ac.FindAll(haystack)

for _, match := range matches {
  println(haystack[match.Start():match.End()])
}

Matching can be done via NFA or DFA. NFA has runtime complexity O(N + M) in relation to the haystack and number of matches. DFA has runtime complexity O(N), but it uses more memory.

Replacing of matches in the haystack.

replaceWith needs to be the same length as the patterns

r := NewReplacer(ac)
replaced := r.ReplaceAll(haystack, replaceWith)

replaced := r.ReplaceAllFunc(haystack, func(match Match) (string, bool) {
    return `<a>` + haystack[match.Start():match.End()] + `<\a>`, true
})

iter := ac.Iter(haystack)

for next := iter.Next(); next != nil; next = iter.Next() {
    ...
}

var w sync.WaitGroup

w.Add(50)
for i := 0; i < 50; i++ {
    go func() {
        ac := ac
        matches := ac.FindAll(haystack)
        println(len(matches))
        w.Done()
    }()
}
w.Wait()