open Noun

let rec nock subject formula =
  match formula with
  | Atom _ -> raise Exit
  | Cell (head_node, tail_node) -> (
      match head_node with
      | Atom op when Z.fits_int op ->
          let opcode = Z.to_int op in
          begin match opcode with
          | 0 ->
              let axis = match tail_node with
                | Atom z -> z
                | _ -> raise Exit
              in
              slot axis subject
          | 1 ->
              tail_node
          | 2 ->
              if not (is_cell tail_node) then raise Exit;
              let b = head tail_node in
              let c = tail tail_node in
              let new_subject = nock subject b in
              let new_formula = nock subject c in
              nock new_subject new_formula
          | 3 ->
              let res = nock subject tail_node in
              if is_cell res then zero else one
          | 4 ->
              let res = nock subject tail_node in
              inc res
          | 5 ->
              let res = nock subject tail_node in
              if not (is_cell res) then raise Exit;
              let a = head res in
              let b = tail res in
              if equal a b then zero else one
          | 6 ->
              if not (is_cell tail_node) then raise Exit;
              let b = head tail_node in
              let rest = tail tail_node in
              if not (is_cell rest) then raise Exit;
              let c = head rest in
              let d = tail rest in
              let test = nock subject b in
              begin match test with
              | Atom z when Z.equal z Z.zero -> nock subject c
              | Atom z when Z.equal z Z.one -> nock subject d
              | _ -> raise Exit
              end
          | 7 ->
              if not (is_cell tail_node) then raise Exit;
              let b = head tail_node in
              let c = tail tail_node in
              let new_subject = nock subject b in
              nock new_subject c
          | 8 ->
              if not (is_cell tail_node) then raise Exit;
              let b = head tail_node in
              let c = tail tail_node in
              let value = nock subject b in
              let new_subject = cell value subject in
              nock new_subject c
          | 9 ->
              if not (is_cell tail_node) then raise Exit;
              let b = head tail_node in
              let c = tail tail_node in
              let axis = match b with
                | Atom z -> z
                | _ -> raise Exit
              in
              let core = nock subject c in
              let target = slot axis core in
              nock core target
          | 10 ->
              if not (is_cell tail_node) then raise Exit;
              let _p = head tail_node in
              let q = tail tail_node in
              nock subject q
          | 11 ->
              if not (is_cell tail_node) then raise Exit;
              let _p = head tail_node in
              let q = tail tail_node in
              nock subject q
          | _ ->
              raise Exit
          end
      | _ ->
          let left = nock subject head_node in
          let right = nock subject tail_node in
          cell left right)

let nock_on subject formula = nock subject formula