Rob pike regex matcher in go

regexp.go

// Match reports whether regexp matches anywhere in text.
func Match(regexp, text string) bool {
    if regexp != "" && regexp[0] == '^' {
        return matchHere(regexp[1:], text)
    }
    for {
        if matchHere(regexp, text) {
            return true
        }
        if text == "" {
            return false
        }
        text = text[1:]
    }
}

// matchHere reports whether regexp matches at beginning of text.
func matchHere(regexp, text string) bool {
    switch {
    case regexp == "":
        return true
    case regexp == "$":
        return text == ""
    case len(regexp) >= 2 && regexp[1] == '*':
        return matchStar(regexp[0], regexp[2:], text)
    case text != "" && (regexp[0] == '.' || regexp[0] == text[0]):
        return matchHere(regexp[1:], text[1:])
    }
    return false
}

// matchStar reports whether c*regexp matches at beginning of text.
func matchStar(c byte, regexp, text string) bool {
    for {
        if matchHere(regexp, text) {
            return true
        }
        if text == "" || (text[0] != c && c != '.') {
            return false
        }
        text = text[1:]
    }
}