import os fn regex_match(src string, pat string) bool { src_size := src.len + 1 pat_size := pat.len + 1 mut memo := [][]int{len: src_size, init: []int{len: pat_size, init: -1}} return regex_match_core(src, pat, 0, 0, mut memo) } fn regex_match_core(src string, pat string, src_pos int, pat_pos int, mut memo [][]int) bool { if memo[src_pos][pat_pos] != -1 { return memo[src_pos][pat_pos] == 1 } mut spos := src_pos mut ppos := pat_pos if spos >= src.len && ppos >= pat.len { memo[src_pos][pat_pos] = 1 return true } else if spos < src.len && ppos >= pat.len { memo[src_pos][pat_pos] = 0 return false } else if spos >= src.len && ppos < pat.len { if pat[ppos] == `\\` { ppos++ } res := ppos + 1 < pat.len && pat[ppos + 1] in [`*`, `?`] && regex_match_core(src, pat, spos, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else { first_is_bslash := pat[ppos] == `\\` if first_is_bslash { ppos++ } first_bslash_and_match := first_is_bslash && ppos < pat.len && (((pat[ppos] == `d` && src[spos].is_digit()) || (pat[ppos] == `D` && !src[spos].is_digit()) || (pat[ppos] == `s` && src[spos].is_space()) || (pat[ppos] == `S` && !src[spos].is_space()) || (pat[ppos] == `w` && (src[spos].is_digit() || src[spos].is_letter() || src[spos] == `_`)) || (pat[ppos] == `W` && !(src[spos].is_digit() || src[spos].is_letter() || src[spos] == `_`))) || (pat[ppos] in [`d`, `D`, `s`, `S`, `w`, `W`] && ppos + 1 < pat.len && pat[ppos + 1] in [`*`, `?`, `+`]) || (pat[ppos] !in [`d`, `D`, `s`, `S`, `w`, `W`] && src[spos] == pat[ppos])) if ppos + 1 < pat.len { match pat[ppos + 1] { `*` { if first_bslash_and_match { res := regex_match_core(src, pat, spos + 1, ppos - 1, mut memo) || regex_match_core(src, pat, spos, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else if src[spos] == pat[ppos] || pat[ppos] == `.` { res := regex_match_core(src, pat, spos + 1, ppos, mut memo) || regex_match_core(src, pat, spos, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else { res := regex_match_core(src, pat, spos, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } } `+` { if first_bslash_and_match { res := regex_match_core(src, pat, spos + 1, ppos - 1, mut memo) || regex_match_core(src, pat, spos + 1, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else if src[spos] == pat[ppos] || pat[ppos] == `.` { res := regex_match_core(src, pat, spos + 1, ppos, mut memo) || regex_match_core(src, pat, spos + 1, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else { memo[src_pos][pat_pos] = 0 return false } } `?` { if first_bslash_and_match || src[spos] == pat[ppos] || pat[ppos] == `.` { res := regex_match_core(src, pat, spos + 1, ppos + 2, mut memo) || regex_match_core(src, pat, spos, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else { res := regex_match_core(src, pat, spos, ppos + 2, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } } else {} } } if first_is_bslash { res := first_bslash_and_match && regex_match_core(src, pat, spos + 1, ppos + 1, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } else { res := (src[spos] == pat[ppos] || pat[ppos] == `.`) && pat[ppos] != `\\` && regex_match_core(src, pat, spos + 1, ppos + 1, mut memo) memo[src_pos][pat_pos] = if res { 1 } else { 0 } return res } } } fn main() { mut cnt := 0 println('currently supported patterns: . ? + * \\ \\d \\D \\s \\S \\w \\W') println('example: source `address@domain.net` matches pattern `\\w+@domain\\.net`') println('enter `exit` to quit\n') for { cnt++ src := os.input('[$cnt] enter source string: ') if src == 'exit' { break } pat := os.input('[$cnt] enter pattern string: ') if pat == 'exit' { break } println('[$cnt] whether `$src` matches `$pat`: ${regex_match(src, pat)}') } }