module Relational =
struct
  open GT
  open OCanren
  open OCanren.Std

  type data_ground = Nat.ground (* with show, gmap *)
  [@@deriving gt ~options:{ show; gmap }]
  type data_logic = Nat.logic
  [@@deriving gt ~options:{ show; gmap }]
  type data_injected = Nat.injected

  module ReadCap = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec t = Rd | NRd
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = t
    ]
  end

  module WriteCap = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec t = AlwaysWr | MayWr | NeverWr
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = t
    ]
  end

  module CopyCap = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec t = Rf | Cp
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = t
    ]

  end

  module InCap = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec t = In | NIn
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = t
    ]
  end

  module OutCap = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec t = Out | NOut
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = t
    ]
  end

  module Mode = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('i, 'o) t = Mode of 'i * 'o
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = (InCap.ground, OutCap.ground) t
    ]

    (* constructors *)
    let n_val = let open InCap in
                let open OutCap in
                ocanren { Mode (NIn, NOut) }
    let i_val = let open InCap in
                let open OutCap in
                ocanren { Mode (In, NOut) }
    let o_val = let open InCap in
                let open OutCap in
                ocanren { Mode (NIn, Out) }
    let io_val = let open InCap in
                 let open OutCap in
                 ocanren { Mode (In, Out) }

    (* accessors *)
    let is_ino m = let open InCap in ocanren {
                     fresh o_ in
                     m == Mode (In, o_) }
    let is_not_ino m = let open InCap in ocanren {
                         fresh o_ in
                         m == Mode (NIn, o_) }
    let is_outo m = let open OutCap in ocanren {
                      fresh i_ in
                      m == Mode (i_, Out) }
    let is_not_outo m = let open OutCap in ocanren {
                          fresh i_ in
                          m == Mode (i_, NOut) }

    (* module Test = struct *)
      (* @type answer = logic GT.list with show *)

      (* let test _ = show(answer) (Stream.take (run q (fun q -> let open InCap in *)
                                                              (* let open OutCap in *)
                                                              (* ocanren {q == Mode (In, NOut)}) *)
                                                    (* (fun q -> q#reify reify))) *)
    (* end *)
  end

  (* TODO: access: data or int ? *)
  module Path = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('d, 'p) t = VarP of 'd | DerefP of 'p | AccessP of 'p * 'd
      [@@deriving gt ~options:{ show; gmap }]
      type ground = (Nat.ground, ground) t
    ]
  end

  module Type = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('r, 'w, 'c, 't, 'tl, 'mtl) t = UnitT of 'r * 'w | RefT of 'c * 't | TupleT of 'tl | FunT of 'mtl
      [@@deriving gt ~options:{ show; gmap }]
      type ground = (ReadCap.ground, WriteCap.ground, CopyCap.ground, ground, ground List.ground, (Mode.ground * ground) List.ground) t
    ]
  end

  (* moded type - no separated type ? *)

  module Expr = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('d, 'p, 'el) t = UnitE | PathE of 'p | RefE of 'd | TupleE of 'el
      [@@deriving gt ~options:{ show; gmap }]
      type ground = (Nat.ground, Path.ground, ground List.ground) t
    ]
  end

  module Stmt = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('p, 'el, 's) t = SkipS | CallS of 'p * 'el | WriteS of 'p | ReadS of 'p | SeqS of 's * 's | ChoiceS of 's * 's
      [@@deriving gt ~options:{ show; gmap }]
      type ground = (Path.ground, Expr.ground List.ground, ground) t
    ]
  end

  (* TODO: list of 3 is not impelmented ?, replaced with two lists for now *)
  module Decl = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('d, 't, 'e, 'dl, 'mtl, 's) t = VarD of 'd * 't * 'e | FunD of 'd * 'dl * 'mtl * 's
      [@@deriving gt ~options:{ show; gmap }]
      type ground = (Nat.ground, Type.ground, Expr.ground, Nat.ground List.ground, (Mode.ground * Type.ground) List.ground, Stmt.ground) t
    ]
  end

  module Prog = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('dl, 's) t = Prog of 'dl * 's
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = (Decl.ground List.ground, Stmt.ground) t
    ]
  end

  (* NOTE: deepvalue - not used (?) *)

  module Value = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('sl, 'd, 'vl) t = ZeroV | SmthV | BotV | FunV of 'sl | RefV of 'd | TupleV of 'vl
      [@@deriving gt ~options:{ show; gmap }]
      type ground = ((Nat.ground List.ground * Stmt.ground) List.ground, Nat.ground, ground List.ground) t
    ]
  end

  (* --- *)

  module Mem = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('vl, 'd) t = Mem of 'vl * 'd
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = (Value.ground List.ground, Nat.ground) t
    ]
  end

  module Types = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec 'dtl t = Types of 'dtl
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = ((Nat.ground * Type.ground) List.ground) t
    ]
  end

  module Vals = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec 'ddl t = Vals of 'ddl
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = ((Nat.ground * Nat.ground) List.ground) t
    ]
  end

  module St = struct
    [@@@warning "-26-27-32-33-34-35-36-37-38-39-60-66-67"]
    [%%ocanren_inject
      type nonrec ('mem, 'types, 'vals) t = St of 'mem * 'types * 'vals
      [@@deriving gt ~options:{ show; gmap }]
      type nonrec ground = (Mem.ground, Types.ground, Vals.ground) t
    ]
  end

  (* --- *)

  (* - utils *)

  let rec list_replaceo xs id value ys = ocanren {
    (* xs == [] & ys == [] | (* NOTE: error *) *)
    { fresh x, xs' in
        xs == x :: xs' &
        id == Nat.o &
        ys == value :: xs' } |
    { fresh x, xs', id', ys' in
        xs == x :: xs' &
        id == Nat.s id' &
        ys == x :: ys' &
        list_replaceo xs' id' value ys' }
  }

  let rec list_ntho xs id x' = ocanren {
    (* xs == [] | (* NOTE: error *) *)
    { fresh y', xs' in
      id == Nat.o &
      y' :: xs' == xs &
      x' == y' } |
    { fresh id', y', xs' in
      Nat.s id' == id &
      y' :: xs' == xs &
      list_ntho xs' id' x' }
  }

  let mem_geto mem id v = ocanren {
    fresh mem_data, mem_len, rev_id  in
    Std.pair mem_data mem_len == mem &
    Nat.addo (Nat.s rev_id) id mem_len &
    list_ntho mem_data rev_id v
  }

  let mem_addo mem v mem_with_id' = ocanren {
    fresh mem_data, mem_len, mem' in
    Std.pair mem_data mem_len == mem &
    mem' == Std.pair (v :: mem_data) (Nat.s mem_len) &
    Std.pair mem' mem_len == mem_with_id'
  }

  let mem_seto mem id v mem' = ocanren {
    fresh mem_data, mem_len, rev_id, mem_data' in
    Std.pair mem_data mem_len == mem &
    Nat.addo (Nat.s rev_id) id mem_len &
    list_replaceo mem_data rev_id v mem_data' &
    Std.pair mem_data' mem_len == mem'
  }

  (* --- FIXME --- CURRENT REWRITE POINT --- FIXME --- *)

  (* --- *)

  (* let rec list_zip_witho f xs ys zs = ocanren { *)
    (* { fresh x, xs', y, ys', z, zs' in *)
      (* xs == x :: xs' & *)
      (* ys == y :: ys' & *)
      (* zs == z :: zs' & *)
      (* f x y z & *)
      (* list_zip_witho f xs' ys' zs' } | *)
    (* { fresh x, xs' in *)
      (* xs == x :: xs' & *)
      (* ys == [] & *)
      (* zs == [] } | *)
    (* { fresh y, ys' in *)
      (* xs == [] & *)
      (* ys == y :: ys' & *)
      (* zs == [] } | *)
    (* { xs == [] & ys == [] & zs == [] } *)
  (* } *)

  (* --- *)

  (* let value_combineo left right res = let open Value in ocanren { *)
    (* { left == Unit & right == Unit & res == Unit } | *)
    (* { left == Bot & right == Bot & res == Bot } | *)
    (* { left == Unit & right == Bot & res == Undef } | *)
    (* { left == Bot & right == Unit & res == Undef } *)
  (* } *)

  (* let memory_combineo left right res = ocanren { *)
    (* list_zip_witho value_combineo left right res *)
  (* } *)

  (* let state_combineo left right res = let open St in ocanren { *)
    (* fresh lenv, lmem, lmem_len, lvisited, renv, rmem, rmem_len, rvisited, res_mem in *)
    (* left == St (lenv, lmem, lmem_len, lvisited) & *)
    (* right == St (renv, rmem, rmem_len, rvisited) & *)
    (* lenv == renv & lmem_len == rmem_len & *)
    (* memory_combineo lmem rmem res_mem  & *)
    (* res == St (lenv, rmem, lmem_len, List.appendo lvisited rvisited) *)
    (* TODO: union visited lists instead ? *)
  (* } *)

  (* --- *)

  (* let rec list_replaceo xs id value ys = ocanren { *)
    (* xs == [] & ys == [] | (* NOTE: error *) *)
    (* { fresh x, xs' in *)
        (* xs == x :: xs' & *)
        (* id == Nat.o & *)
        (* ys == value :: xs' } | *)
    (* { fresh x, xs', id', ys' in *)
        (* xs == x :: xs' & *)
        (* id == Nat.s id' & *)
        (* ys == x :: ys' & *)
        (* list_replaceo xs' id' value ys' } *)
  (* } *)

  (* let env_geto state id tag' mem_id' = *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh env, _mem, _mem_len, _visited, elem in *)
      (* state == St (env, _mem, _mem_len, _visited) & *)
      (* List.assoco id env elem & *)
      (* Std.pair tag' mem_id' == elem *)
  (* } *)

  (* let env_addo state id tg mem_id state' = *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh env, env', mem, mem_len, visited, elem in *)
      (* state == St (env, mem, mem_len, visited) & *)
      (* Std.pair tg mem_id == elem & *) 
      (* (Std.pair id elem) :: env == env' & *)
      (* state' == St (env', mem, mem_len, visited) *)
  (* } *)

  (* let inv_ido mem_len id id' = ocanren { *)
    (* fresh inv_id_inc in *)
      (* Nat.addo inv_id_inc id mem_len & *)
      (* Nat.addo id' 1 inv_id_inc *)
  (* } *)

  (* --- *)

  (* let rec list_ntho xs id x' = ocanren { *)
    (* xs == [] | (* NOTE: error *) *)
    (* { fresh y', xs' in *)
      (* id == Nat.o & *)
      (* y' :: xs' == xs & *)
      (* x' == y' } | *)
    (* { fresh id', y', xs' in *)
      (* Nat.s id' == id & *)
      (* y' :: xs' == xs & *)
      (* list_ntho xs' id' x' } *)
  (* } *)

  (* let mem_geto state id value' = *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh mem, mem_len, mem_id, mem_id_inv, _env, _visited, _tag in *)
    (* state == St (_env, mem, mem_len, _visited) & *)
    (* env_geto state id _tag mem_id & *)
    (* inv_ido mem_len mem_id mem_id_inv & *)
    (* list_ntho mem mem_id_inv value' *)
  (* } *)

  (* let mem_seto state id value state'= *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh env, mem, mem_len, visited, mem_id, inv_mem_id, mem', _tag in *)
      (* state == St (env, mem, mem_len, visited) & *)
      (* env_geto state id _tag mem_id & *)
      (* inv_ido mem_len mem_id inv_mem_id & *)
      (* list_replaceo mem inv_mem_id value mem' & *)
      (* state' == St (env, mem', mem_len, visited) *)
  (* } *)

  (* let mem_addo state value state' = *)
    (* let open St in *)
    (* ocanren { *)
      (* fresh env, mem, mem_len, mem_len', visited, mem' in *)
      (* state == St (env, mem, mem_len, visited) & *)
      (* mem' == value :: mem & *)
      (* mem_len' == Nat.s mem_len & *)
      (* state' == St (env, mem', mem_len', visited) *)
  (* } *)

  (* let mem_checko state id = *)
    (* let open Value in *)
    (* ocanren { *)
      (* mem_geto state id Unit *)
    (* } *)

  (* --- *)

  (* let rec list_foldlo f acc xs acc' = ocanren { *)
    (* xs == [] & acc' == acc | *)
    (* { fresh x', xs', acc_upd in *)
      (* xs == x' :: xs' & *)
      (* list_foldlo f acc xs' acc_upd & *)
      (* f acc_upd x' acc' } *)
  (* } *)

  (* let rec list_foldro f acc xs acc' = ocanren { *)
    (* xs == [] & acc' == acc | *)
    (* { fresh x', xs', acc_upd in *)
      (* xs == x' :: xs' & *)
      (* f acc x' acc_upd & *)
      (* list_foldro f acc_upd xs' acc' } *)
    (* TODO: inf search on swap, investigate *)
  (* } *)


  (* let rec list_foldr2o f acc xs ys acc' = ocanren { *)
    (* xs == [] & ys == [] & acc' == acc | *)
    (* { fresh x', xs', y', ys', acc_upd in *)
      (* xs == x' :: xs' & *)
      (* ys == y' :: ys' & *)
      (* f acc x' y' acc_upd & *)
      (* list_foldr2o f acc_upd xs' ys' acc' } *)
  (* } *)

  (* let rec list_foldl2o f acc xs ys acc' = ocanren { *)
    (* xs == [] & ys == [] & acc' == acc | *)
    (* { fresh x', xs', y', ys', acc_upd in *)
      (* xs == x' :: xs' & *)
      (* ys == y' :: ys' & *)
      (* list_foldl2o f acc xs' ys' acc_upd & *)
      (* f acc_upd x' y' acc' } *)
  (* } *)

  (* let arg_to_valueo state arg value' = *)
    (* let open Arg in *)
    (* let open Value in *)
    (* ocanren { *)
    (* arg == RValue & value' == Unit | *)
    (* { fresh id in *)
      (* arg == LValue id & *)
      (* mem_geto state id value' } *)
  (* } *)

  (* let arg_to_rvalueo arg value' = *)
    (* let open Arg in *)
    (* let open Tag in *)
    (* ocanren { is_valueo arg & value' == RValue } *)

  (* let st_mem_leno state mem_len' = *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh _env, _mem, _visited in *)
      (* state == St (_env, _mem, mem_len', _visited) *)
  (* } *)

  (* let tag_correcto tg = *)
    (* let open Tag in *)
    (* ocanren { *)
      (* {is_not_outo tg | { is_outo tg & is_always_writeo tg } } & *)
      (* {is_not_reado tg | { is_reado tg & is_ino tg } } *)
    (* } *)

  (* let st_add_argo state state_before id arg_tag arg state'' = *)
    (* let open Nat in *)
    (* let open Value in *)
    (* let open Arg in *)
    (* let open Tag in *)
    (* ocanren { *)
        (* tag_correcto arg_tag & { *)
        (* { fresh value', state', mem_len_prev' in *)
          (* is_valueo arg_tag & *)
          (* arg_to_valueo state_before arg value' & *)
          (* mem_addo state value' state' & *)
          (* st_mem_leno state mem_len_prev' & *)
          (* env_addo state' id arg_tag mem_len_prev' state'' } | *)
        (* { fresh arg', parent_tag, mem_id, state' in *)
          (* is_refo arg_tag & *)
            (* { arg == RValue } *) (* NOTE: not allowed for now *)
          (* arg == LValue arg' & *)
          (* env_geto state_before id parent_tag mem_id & *)
          (* env_addo state id arg_tag mem_id state' & *)
          (* { is_never_writeo arg_tag | { is_may_writeo arg_tag & is_may_writeo parent_tag } } & *)
          (* { *)
            (* { is_reado arg_tag & state' == state'' } | *)
            (* { is_not_reado arg_tag & mem_seto state' id Bot state'' } *)
          (* } *)
        (* } *)
      (* } *)
    (* } *)

  (* let st_spoil_foldero state_before state tg id state' = *)
    (* let open Value in *)
    (* let open Tag in *)
    (* let open St in *)
    (* ocanren { *)
      (* fresh env, mem, mem_len, _visited, parent_tg, _mem_id in *)
      (* state == St (env, mem, mem_len, _visited) & *)
      (* env_geto state id parent_tg _mem_id & *)
      (* { is_not_reado tg | { is_reado tg & mem_checko state_before id } } & *)
      (* { { is_never_writeo tg & state == state'} | *)
        (* { is_always_writeo tg & *) 
          (* is_outo tg & is_may_writeo parent_tg & mem_seto state id Unit state' } | *)
        (* { is_may_writeo tg & { *)
          (* { is_not_outo tg & is_valueo tg & state == state' } | *)
          (* { is_not_outo tg & is_refo tg & is_may_writeo parent_tg & mem_seto state id Bot state' } *)
        (* } } *)
      (* } *)
    (* } *)

  (* let st_spoil_by_argso state arg_tags args state' = *)
    (* ocanren { *)
      (* fresh state_before in *)
      (* state == state_before & (* TODO: required ? *) *)
      (* list_foldl2o (st_spoil_foldero state_before) state arg_tags args state' *)
    (* } *)

  (* let st_spoil_assignmentso state state' = *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh _env, _mem, _mem_len, visited in *)
      (* state == St (_env, _mem, _mem_len, visited) & *)
      (* list_foldlo st_spoil_foldero state visited state' *)
  (* } *)

  (* --- *)

  (* let arg_to_lvalueo arg arg' = *)
    (* let open Arg in *)
    (* ocanren { arg' == LValue arg } *)

  (* let rec list_dropo n xs xs' = ocanren { *)
    (* xs == [] & xs' == [] | *)
    (* n == Nat.o & xs == xs' & xs =/= [] | *)
    (* { fresh n', _y, ys in *)
        (* Nat.s n' == n & *)
        (* xs == _y :: ys & *)
        (* list_dropo n' ys xs' } *)
  (* } *)

  (* let rec list_not_membero xs x = ocanren { *)
    (* xs == [] | *)
    (* { fresh x', xs' in *)
        (* xs == x' :: xs' & *)
        (* x' =/= x & *)
        (* list_not_membero xs' x } *)
  (* } *)

  (* let visited_checko state f_id = *)
    (* let open St in *)
    (* ocanren { *)
      (* fresh _env, _mem, _mem_len, visited in *)
      (* state == St (_env, _mem, _mem_len, visited) & *)
      (* List.membero visited f_id *)
    (* } *)

  (* let not_visited_checko state f_id = *)
    (* let open St in *)
    (* ocanren { *)
      (* fresh _env, _mem, _mem_len, visited in *)
      (* state == St (_env, _mem, _mem_len, visited) & *)
      (* list_not_membero visited f_id *)
    (* } *)

  (* let visited_addo state f_id state' = *)
    (* let open St in *)
    (* ocanren { *)
      (* fresh env, mem, mem_len, visited, visited' in *)
      (* state == St (env, mem, mem_len, visited) & *)
      (* visited' == f_id :: visited & *)
      (* state' == St (env,mem, mem_len, visited') *)
    (* } *)

  (* let rec eval_stmto state prog stmt state' = *)
    (* let open Stmt in *)
    (* let open Value in *)
    (* let open FunDecl in *)
    (* let open Tag in *)
    (* ocanren { *)
    (* { fresh f_id, args, f, args', state_after_call, arg_tags, _body in *)
      (* stmt == Call (f_id, args) & *)
      (* list_ntho prog f_id f & *)
      (* FunDecl (arg_tags, _body) == f & *)
      (* List.mapo arg_to_lvalueo args args' & *)
      (* TODO: FIXME: memoisation, do not do calls on check successfull *)
      
      (* NOTE: tmp simplification for less branching (TODO?) *)
      (* { { fresh state_with_visited in *)
          (* not_visited_checko state f_id & *)
          (* visited_addo state f_id state_with_visited & *)
          (* eval_funo state_with_visited prog f args' state_after_call } | *)
        (* { visited_checko state f_id & *)
          (* state_after_call == state } } & *)
      (* st_spoil_by_argso state_after_call arg_tags args state' } | *)
    (* { fresh id in stmt == Read id & mem_checko state id & state == state' } | *)
    (* { fresh id, tag, _mem_id in *)
      (* stmt == Write id & *)
      (* env_geto state id tag _mem_id & *)
      (* is_may_writeo tag & *)
      (* mem_seto state id Unit state' } | *)
    (* { fresh xs, ys in *)
      (* stmt == Choice (xs, ys) } *)
    (* TODO: FIXME: choice actions *)
  (* } *)

  (* and eval_body_foldero prog state stmt state' = *)
    (* eval_stmto state prog stmt state' *)

  (* and eval_bodyo state prog body state' = *)
    (* list_foldro (eval_body_foldero prog) state body state' *) 

  (* and add_arg_foldero state_before state_c arg_tag arg state_c' = *)
    (* ocanren { *)
    (* fresh state, id, state', id' in *)
      (* state_c == Std.pair state id & *)
      (* st_add_argo state state_before id arg_tag arg state' & *)
      (* id' == Nat.s id & *)
      (* state_c' == Std.pair state' id' *)
  (* } *)

  (* and eval_funo state prog decl args state' = *)
    (* let open FunDecl in *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh arg_tags, body, *)
          (* env_before, mem_before, len_before, visited_before, *)
          (* state_clean, *)
          (* state_with_vars, _counter, *)
          (* state_evaled, *)
          (* _env, _mem, _len, visited, *)
          (* nil_env, nil_visited in *)
      (* nil_env == [] & *)
      (* nil_visited == [] & *)
      (* decl == FunDecl (arg_tags, body) & *)
      (* state == St (env_before, mem_before, len_before, visited_before) & *)
      (* state_clean == St (nil_env, mem_before, len_before, nil_visited) & *)
      (* list_foldr2o (add_arg_foldero state) *)
                   (* (Std.pair state Nat.o) arg_tags args *)
                   (* (Std.pair state_with_vars _counter) & (* TODO: or foldr2o ?? *) *)
      (* eval_bodyo state_with_vars prog body state_evaled & *)
      (* state_evaled == St (_env,_mem, _len, visited) & *)
      (* state' == St (env_before, mem_before, len_before, visited) *)
  (* } *)

  (* and eval_fun_empty_argso state prog decl state' = *)
    (* let open FunDecl in *)
    (* ocanren { *)
    (* fresh arg_tags, args, _body in *)
      (* decl == FunDecl (arg_tags, _body) & *)
      (* List.mapo arg_to_rvalueo arg_tags args & *)
      (* eval_funo state prog decl args state' *)
  (* } *)

  (* --- *)

  (* let empty_stateo state = *)
    (* let open St in *)
    (* ocanren { *)
    (* fresh nil_env, nil_mem, nil_visited in *)
      (* nil_env == [] & *)
      (* nil_visited == [] & *)
      (* nil_mem == [] & *)
      (* state == St (nil_env, nil_mem, Nat.o, nil_visited) *)
  (* } *)

  (* let eval_progo all_prog state' = *)
    (* let open Prog in *)
    (* ocanren { *)
    (* fresh prog, main_decl, state in *)
      (* all_prog == Prog (prog, main_decl) & *)
      (* empty_stateo state & *)
      (* eval_fun_empty_argso state prog main_decl state' *)
  (* } *)
end