Lookaround = object
  ahead*: AheadSig
  behind*: BehindSig
  smL*: SmLookaround

func lookAround(ntn: Node; capts: var Capts3; captIdx: var int32; text: string;
                look: var Lookaround; start: int; flags: MatchFlags): bool {.
    ...raises: [], tags: [RootEffect].}

func matchImpl(text: string; regex: Regex; m: var RegexMatch2; start = 0;
               flags: MatchFlags = {}): bool {....raises: [], tags: [RootEffect].}

func reversedMatchImpl(smA, smB: var Submatches; text: string; nfa: Nfa;
                       look: var Lookaround; groupsLen: int; start, limit: int;
                       flags: MatchFlags = {}): int {....raises: [],
    tags: [RootEffect].}

func startsWithImpl2(text: string; regex: Regex; start: int): bool {....raises: [],
    tags: [RootEffect].}

template initLook(): Lookaround