diff --git a/lib/dune b/lib/dune
index 7791c5e..a4e98e3 100644
--- a/lib/dune
+++ b/lib/dune
@@ -1,7 +1,7 @@
-(env
- (_
-  (flags
-   (:standard -warn-error +5))))
+; (env
+;  (_
+;   (flags
+;    (:standard -warn-error +5))))
 
 (library
  (name semantic_interpreter)
@@ -26,7 +26,7 @@
  (flags
   (:standard -rectypes))
  (libraries OCanren OCanren.tester)
- (preprocessor_deps %{project_root}/lib/pp5+gt+plugins+ocanren+dump.exe)
+ (preprocessor_deps ./pp5+gt+plugins+ocanren+dump.exe)
  (inline_tests)
  (wrapped false)
  (preprocess
diff --git a/lib/relational_semantic_interpreter.ml b/lib/relational_semantic_interpreter.ml
index 1163292..a1e5cd6 100644
--- a/lib/relational_semantic_interpreter.ml
+++ b/lib/relational_semantic_interpreter.ml
@@ -45,155 +45,229 @@ struct
   type env_injected = (data_injected * data_injected) List.injected ilogic
 
   @type ('env, 'mem, 'last_mem, 'assignments) state_abs =  'env * 'mem * 'last_mem * 'assignments with show, gmap
-  @type state_ground = (list_map_ground, value_ground List.ground, data_ground, data_ground List.ground) state_abs with show, gmap
-  @type state_logic = (list_map_logic, value_logic List.logic, data_logic, data_logic List.logic) state_abs logic with show, gmap
+  @type state_ground = (env_ground, value_ground List.ground, data_ground, data_ground List.ground) state_abs with show, gmap
+  @type state_logic = (env_logic, value_logic List.logic, data_logic, data_logic List.logic) state_abs logic with show, gmap
   type state_injected = (env_injected, value_injected List.injected, data_injected, data_injected List.injected) state_abs ilogic
 
   (* ocanren type 'a lst = Nil | Cons of 'a * 'a lst *)
 
   let rec list_replace xs id value ys =
     conde
-    [ (xs === List.nil) (ys === List.nil) (* TODO: error *)
-    ; fresh (x xs') (xs === List.cons x xs') (id === 0) (ys === List.cons value xs)
-    ; fresh (x xs' id' ys') (xs ===List. cons x xs') (id === Nat.succ id') (ys === List.cons x ys')
+    [ (xs === Std.nil ()) &&& (ys === Std.nil ()) (* TODO: error *)
+    ; fresh (x xs') (xs === List.cons x xs') (id === Nat.o) (ys === List.cons value xs)
+    ; fresh (x xs' id' ys') (xs === List. cons x xs') (id === Nat.s id') (ys === List.cons x ys')
                             (list_replace xs' id' value ys')
     ]
 
-  let env_get state id state' =
-    fresh (env env' mem mem_len assignments)
-    (state === (env, mem, mem_len, assignments))
-    (state' === (env', mem,  mem_len, assignments))
-    (List.assoco id env env')
+  let rec list_assoc a xs v' =
+    conde
+    [ fresh (a' b' xs')
+      (xs === List.cons (a', b') xs')
+      (a =/= a')
+      (list_assoc a xs' v')
+    ; fresh (a' b' xs')
+      (xs === List.cons (a', b') xs')
+      (a === a')
+      (v' === b')
+    ]
+  (* TODO: dofference from List.assoco ?? *)
+
+  let env_get state id mem_id' =
+    fresh (env mem mem_len assignments)
+    (state === inj (env, mem, mem_len, assignments))
+    (list_assoc id env mem_id')
+    (* (List.assoco id env mem_id') *)
 
   let env_add state id mem_id state' =
     fresh (env env' mem mem_len assignments)
-    (state === (env, mem, mem_len, assignments))
-    (state' === (env', mem,  mem_len, assignments))
-    (env' == List.cons (id, mem_id) env)
+    (state === inj (env, mem, mem_len, assignments))
+    (state' === inj (env', mem,  mem_len, assignments))
+    (env' === List.cons (id, mem_id) env)
 
   let inv_id mem_len id id' =
-    (fresh inv_id_inc)
+    fresh (inv_id_inc)
     (Nat.addo inv_id_inc id mem_len)
-    (Nat.addo id' 1 inv_id_inc)
+    (Nat.addo id' (Nat.s Nat.o) inv_id_inc)
 
   (* --- *)
 
-  let list_nth xs id x' =
+  let rec list_nth xs id x' =
    conde
-   [ (xs === List.nil) (* TODO: error *)
-   ; (fresh y' xs') (id === 0) (List.cons y' xs' === xs) (x' === y')
-   ; (fresh id' y' xs') (Nat.succ id' === id) (List.cons y' xs' === xs) (list_nth xs' id' x')
+   [ (xs === Std.nil ()) (* TODO: error *)
+   ; fresh (y' xs') (id === Nat.o) (List.cons y' xs' === xs) (x' === y')
+   ; fresh (id' y' xs') (Nat.s id' === id) (List.cons y' xs' === xs) (list_nth xs' id' x')
    ]
 
+  (* TODO: use real holes *)
   let mem_get state id value' =
-    (fresh mem mem_len)
-    (state === (_, mem, mem_len, _))
-    (fresh mem_id mem_id_inv)
+    fresh (mem mem_len mem_id mem_id_inv env_ assignments_)
+    (state === inj (env_, mem, mem_len, assignments_))
     (env_get state id mem_id)
-    (inv_id mem_len mem_id mem_len_inv)
-    (list_nth mem mem_id value')
+    (inv_id mem_len mem_id mem_id_inv)
+    (list_nth mem mem_id_inv value')
 
   let mem_set state id value state'=
-    (fresh env mem mem_len assignments)
-    (state === (env, mem, mem_len, assignments))
-    (fresh mem_id) (env_get state id mem_id)
-    (fresh inv_mem_id) (inv_id mem_len mem_id inv_mem_id)
-    (fresh mem') (list_replace mem mem_id value mem')
-    (state' === (env, mem', mem_len, List.cons id assignments))
+    fresh (env mem mem_len assignments mem_id inv_mem_id mem')
+    (state === inj (env, mem, mem_len, assignments))
+    (env_get state id mem_id)
+    (inv_id mem_len mem_id inv_mem_id)
+    (list_replace mem mem_id value mem')
+    (state' === inj (env, mem', mem_len, List.cons id assignments))
 
   let mem_add state value state' =
-    (fresh env mem mem_len assignments)
-    (state === (env, mem, mem_len, assignments))
-    (fresh mem') (mem' === List.cons value mem)
-    (state' === (env, mem, Nat.succ mem_len, assignments))
+    fresh (env mem mem_len assignments mem')
+    (state === inj (env, mem, mem_len, assignments))
+    (mem' === List.cons value mem)
+    (state' === inj (env, mem, Nat.s mem_len, assignments))
 
   let mem_check state id state' =
     conde
-    [ (mem_get state id BotV) (state' === state) (* TODO: error *)
-    ; (mem_get state id UnitV) (state' === state)
+    [ (mem_get state id (inj BotV)) &&& (state' === state) (* TODO: error *)
+    ; (mem_get state id (inj UnitV)) &&& (state' === state)
     ]
 
   (* --- *)
 
+  let rec list_foldl f acc xs acc' =
+    conde
+    [ (xs === Std.nil ()) &&& (acc' === acc)
+    ; fresh (x' xs' acc_upd)
+      (xs === List.cons x' xs')
+      (list_foldl f acc xs' acc_upd)
+      (f acc_upd x' acc')
+    ]
+
+
+  let rec list_foldr2 f acc xs ys acc' =
+    conde
+    [ (xs === Std.nil ()) &&& (ys === Std.nil ()) &&& (acc' === acc)
+    ; fresh (x' xs' y' ys' acc_upd)
+      (xs === List.cons x' xs')
+      (ys === List.cons y' ys')
+      (f acc x' y' acc_upd)
+      (list_foldr2 f acc_upd xs' ys' acc')
+    ]
+
+  let rec list_foldl2 f acc xs ys acc' =
+    conde
+    [ (xs === Std.nil ()) &&& (ys === Std.nil ()) &&& (acc' === acc)
+    ; fresh (x' xs' y' ys' acc_upd)
+      (xs === List.cons x' xs')
+      (ys === List.cons y' ys')
+      (list_foldl2 f acc xs' ys' acc_upd)
+      (f acc_upd x' y' acc')
+    ]
+
   let arg_to_value state arg value' =
     conde
-    [ (arg === RValue) (value' === UnitV)
-    ; (fresh id) (arg === LValue id) (mem_get state id value')
+    [ (arg === inj RValue) &&& (value' === inj UnitV)
+    ; fresh (id) (arg === inj (LValue id)) (mem_get state id value')
     ]
 
-  let st_mem_len state mem_len' = (state === (_, _, mem_len, _))
+  let arg_to_rvalue _arg value' = (value' === inj RValue)
+
+  let st_mem_len state mem_len' =
+    fresh (env_ mem_ assignments_) (* TODO: replace with real placeholder ? *)
+    (state === inj (env_, mem_, mem_len', assignments_))
 
   let st_add_arg state state_before id arg_tag arg state'' =
     conde
-    [ (arg_tag === Ref) (arg === RValue) (state'' === state) (* TODO: error *) (* TODO: allow later ?? *)
-    ; (fresh arg') (arg_tag === Ref) (arg === LValue arg')
-      (fresh value') (env_get state_before arg value')
-                     (env_add state id value' state'')
-    ; (arg_tag === Value)
-      (fresh value' state' mem_len_dec')
+    [ (arg_tag === inj Ref) &&& (arg === inj RValue) &&& (state'' === state)
+      (* TODO: error, TODO: allow later ?? *)
+    ; fresh (arg' value')
+      (arg_tag === inj Ref)
+      (arg === inj (LValue arg'))
+      (env_get state_before arg' value')
+      (env_add state id value' state'')
+    ; fresh (value' state' mem_len_dec')
+      (arg_tag === inj Value)
       (arg_to_value state_before arg value')
       (mem_add state value' state')
-      (Nat.succ mem_len_dec' === st_mem_len state)
+      (st_mem_len state (Nat.s mem_len_dec'))
       (env_add state' id mem_len_dec' state'')
     ]
 
+  let st_spoil_folder mem_len state mem id mem' =
+    fresh (mem_id' mem_id_inv')
+    (env_get state id mem_id')
+    (inv_id mem_len mem_id' mem_id_inv')
+    (list_replace mem mem_id_inv' (inj BotV) mem')
+
   let st_spoil_assignments state state' =
-    (fresh env mem mem' mem_len assignments)
-    (state === (env, mem, mem_len, assignments))
-    (List.fold_left (fun mem id -> list_replace mem (inv_id mem_len @@ env_get state id) BotV) mem assignments mem')
-    (* TODO: replace with foldlo (or foldro ?) *)
-    (state') === (env, mem', mem_len, [])
+    fresh (env mem mem' mem_len assignments)
+    (state === inj (env, mem, mem_len, assignments))
+    (list_foldl (st_spoil_folder mem_len state) mem assignments mem')
+    (* (List.fold_left (fun mem id -> list_replace mem (inv_id mem_len @@ env_get state id) BotV) mem assignments mem') *)
+    (state' === inj (env, mem', mem_len, Std.nil ()))
 
   (* --- *)
 
-  let arg_to_lvalue arg arg' = (arg' === LValue arg)
+  let arg_to_lvalue arg arg' = (arg' === inj (LValue arg))
+
+  let rec list_drop n xs xs' =
+    conde
+    [ (xs === Std.nil ()) &&& (xs' === Std.nil ())
+    ; n === Nat.o &&& (xs === xs')
+    ; fresh (n' y ys) (Nat.s n' === n) (xs === List.cons y ys) (list_drop n' ys xs')
+    ]
 
   let rec eval_stmt state prog stmt state' =
     conde
-    [ (fresh f_id args)
-      (stmt === Call (f_id, args))
-      (fresh f args')
+    [ fresh (f_id args f args')
+      (stmt === inj (Call (f_id, args)))
       (list_nth prog f_id f)
       (List.mapo arg_to_lvalue args args')
-      (eval_fun state prog f args')
-    ; (fresh id) (stmt === Read id) (mem_check state id state')
-    ; (fresh id) (stmt === Write id) (mem_set state it UnitV state')
+      (eval_fun state prog f args' state')
+    ; fresh (id) (stmt === inj (Read id)) (mem_check state id state')
+    ; fresh (id) (stmt === inj (Write id)) (mem_set state id (inj UnitV) state')
     ]
 
+  and eval_body_folder prog state stmt state' = eval_stmt state prog stmt state'
+
   and eval_body state prog body state' =
-    (List.fold_left (fun state stmt -> eval_stmt state prog stmt) state body)
-    (* TODO: replace with foldlo (or foldro ?) *)
+    list_foldl (eval_body_folder prog) state body state' 
+    (* (List.fold_left (fun state stmt -> eval_stmt state prog stmt) state body) *)
+
+  and add_arg_folder state_before state_c arg_tag arg state_c' =
+    fresh (state id state' id')
+    (state_c === inj (state, id))
+    (st_add_arg state state_before id arg_tag arg state')
+    (id' === Nat.s id)
+    (state_c' === inj (state', id'))
 
   and eval_fun state prog decl args state' =
-    (fresh arg_tags body)
-    (fresh env_before mem_before len_before assignments_before)
-    (fresh state_clean)
-    (state_clean === ([], mem_before, len_before, []))
-    (fresh state_with_vars)
-    (state_with_vars === List.fold_left2 (fun (state, id) arg_tag arg -> (st_add_arg state state id arg_tag arg, id + 1)) (state, 0) arg_tags args)
-    (* TODO how, rewrite from scratch ??? *)
-    (* TODO: replace with foldlo (or foldro ?) ?? *)
-    (fresh state_evaled)
-    (eval_body state prog body state_evaled)
-    (fresh state_spoiled)
+    fresh (arg_tags body
+           env_before mem_before len_before assignments_before
+           state_clean
+           state_with_vars counter_
+           state_evaled
+           state_spoiled
+           env_ mem_spoiled len assignments_
+           mem_updated len_to_drop)
+    (decl === inj (arg_tags, body))
+    (state === inj (env_before, mem_before, len_before, assignments_before))
+    (state_clean === inj (Std.nil (), mem_before, len_before, Std.nil ()))
+    (list_foldl2 (add_arg_folder state) (inj (state, Nat.o)) arg_tags args (inj (state_with_vars, counter_))) (* TODO: replace with real placeholder *)
+    (eval_body state_with_vars prog body state_evaled)
     (st_spoil_assignments state_evaled state_spoiled)
-    (fresh mem_updated len_to_drop)
+    (state_spoiled === inj (env_, mem_spoiled, len, assignments_))
     (Nat.addo len_to_drop len_before len)
-    (List.drop len_to_drop mem mem_updated)
-    (state' === (env_before, mem_updated, len_before, assignments_before))
+    (list_drop len_to_drop mem_spoiled mem_updated)
+    (state' === inj (env_before, mem_updated, len_before, assignments_before))
 
   and eval_fun_empty_args state prog decl state' =
-    (fresh arg_tags)
-    (decl === (arg_tags, _))
-    (List.mapo arg_to_rvalue arg_tags args) (* TODO how, rewrite from scratch ??? *)
+    fresh (arg_tags args hole_) (* TODO: replace with real placeholder *)
+    (decl === inj (arg_tags, hole_))
+    (List.mapo arg_to_rvalue arg_tags args)
     (eval_fun state prog decl args state')
 
   (* --- *)
 
-  let empty_state state = (state === ([], [], 0, []))
+  let empty_state state = (state === inj (Std.nil (), Std.nil (), Nat.o, Std.nil ()))
 
   let eval_prog all_prog state' =
-    (fresh prog main_decl)
-    (all_prog == (prog, main_decl))
-    (eval_fun_empty_args empty_state prog main_decl state')
+    fresh (prog main_decl state)
+    (all_prog === inj (prog, main_decl))
+    (empty_state state)
+    (eval_fun_empty_args state prog main_decl state')
 end
diff --git a/lib/relational_semantic_interpreter_old.ml b/lib/relational_semantic_interpreter_old.ml
new file mode 100644
index 0000000..af9bb6d
--- /dev/null
+++ b/lib/relational_semantic_interpreter_old.ml
@@ -0,0 +1,200 @@
+
+(* (,,) -< Pair.inj _ (Pair.inj _ _) *)
+
+module Relational =
+struct
+  open GT
+  open OCanren
+  open OCanren.Std
+
+  @type data_ground = Nat.ground with show, gmap
+  @type data_logic = Nat.logic with show, gmap
+  type data_injected = Nat.injected
+
+  @type tag_ground = Ref | Value with show, gmap
+  @type tag_logic = tag_ground logic with show, gmap
+  type tag_injected = tag_ground ilogic
+
+  @type ('d, 'dl) stmt_abs = Call of 'd * 'dl | Read of 'd | Write of 'd with show, gmap
+  @type stmt_ground = (data_ground, data_ground List.ground) stmt_abs with show, gmap
+  @type stmt_logic = (data_logic, data_logic List.logic) stmt_abs logic with show, gmap
+  type stmt_injected = (data_injected, data_injected List.injected) stmt_abs ilogic
+
+  @type body_ground = stmt_ground List.ground with show, gmap
+  @type body_logic = stmt_logic List.logic with show, gmap
+  type body_injected = stmt_injected List.injected
+
+  @type fun_decl_ground = tag_ground List.ground * body_ground with show, gmap
+  @type fun_decl_logic = (tag_logic List.logic * body_logic) logic with show, gmap
+  type fun_decl_injected = (tag_injected List.injected * body_injected) ilogic
+
+  @type prog_ground = fun_decl_ground List.ground * fun_decl_ground with show, gmap
+  @type prog_logic = (fun_decl_logic List.logic * fun_decl_logic) logic with show, gmap
+  type prog_injected = (fun_decl_injected List.injected * fun_decl_injected) ilogic
+
+  @type 'd arg_abs = RValue | LValue of 'd with show, gmap
+  @type arg_ground = data_ground arg_abs with show, gmap
+  @type arg_logic = data_logic arg_abs logic with show, gmap
+  type arg_injected = data_injected arg_abs ilogic
+
+  @type value_ground = UnitV | BotV with show, gmap
+  @type value_logic = value_ground logic with show, gmap
+  type value_injected = value_ground ilogic
+
+  @type env_ground = (data_ground * data_ground) List.ground with show, gmap
+  @type env_logic = (data_logic * data_logic) List.logic with show, gmap
+  type env_injected = (data_injected * data_injected) List.injected ilogic
+
+  @type ('env, 'mem, 'last_mem, 'assignments) state_abs =  'env * 'mem * 'last_mem * 'assignments with show, gmap
+  @type state_ground = (list_map_ground, value_ground List.ground, data_ground, data_ground List.ground) state_abs with show, gmap
+  @type state_logic = (list_map_logic, value_logic List.logic, data_logic, data_logic List.logic) state_abs logic with show, gmap
+  type state_injected = (env_injected, value_injected List.injected, data_injected, data_injected List.injected) state_abs ilogic
+
+  (* ocanren type 'a lst = Nil | Cons of 'a * 'a lst *)
+
+  let rec list_replace xs id value ys =
+    conde
+    [ (xs === List.nil) (ys === List.nil) (* TODO: error *)
+    ; fresh (x xs') (xs === List.cons x xs') (id === 0) (ys === List.cons value xs)
+    ; fresh (x xs' id' ys') (xs ===List. cons x xs') (id === Nat.succ id') (ys === List.cons x ys')
+                            (list_replace xs' id' value ys')
+    ]
+
+  let env_get state id state' =
+    fresh (env env' mem mem_len assignments)
+    (state === (env, mem, mem_len, assignments))
+    (state' === (env', mem,  mem_len, assignments))
+    (List.assoco id env env')
+
+  let env_add state id mem_id state' =
+    fresh (env env' mem mem_len assignments)
+    (state === (env, mem, mem_len, assignments))
+    (state' === (env', mem,  mem_len, assignments))
+    (env' == List.cons (id, mem_id) env)
+
+  let inv_id mem_len id id' =
+    (fresh inv_id_inc)
+    (Nat.addo inv_id_inc id mem_len)
+    (Nat.addo id' 1 inv_id_inc)
+
+  (* --- *)
+
+  let list_nth xs id x' =
+   conde
+   [ (xs === List.nil) (* TODO: error *)
+   ; (fresh y' xs') (id === 0) (List.cons y' xs' === xs) (x' === y')
+   ; (fresh id' y' xs') (Nat.succ id' === id) (List.cons y' xs' === xs) (list_nth xs' id' x')
+   ]
+
+  let mem_get state id value' =
+    (fresh mem mem_len)
+    (state === (_, mem, mem_len, _))
+    (fresh mem_id mem_id_inv)
+    (env_get state id mem_id)
+    (inv_id mem_len mem_id mem_len_inv)
+    (list_nth mem mem_id value')
+
+  let mem_set state id value state'=
+    (fresh env mem mem_len assignments)
+    (state === (env, mem, mem_len, assignments))
+    (fresh mem_id) (env_get state id mem_id)
+    (fresh inv_mem_id) (inv_id mem_len mem_id inv_mem_id)
+    (fresh mem') (list_replace mem mem_id value mem')
+    (state' === (env, mem', mem_len, List.cons id assignments))
+
+  let mem_add state value state' =
+    (fresh env mem mem_len assignments)
+    (state === (env, mem, mem_len, assignments))
+    (fresh mem') (mem' === List.cons value mem)
+    (state' === (env, mem, Nat.succ mem_len, assignments))
+
+  let mem_check state id state' =
+    conde
+    [ (mem_get state id BotV) (state' === state) (* TODO: error *)
+    ; (mem_get state id UnitV) (state' === state)
+    ]
+
+  (* --- *)
+
+  let arg_to_value state arg value' =
+    conde
+    [ (arg === RValue) (value' === UnitV)
+    ; (fresh id) (arg === LValue id) (mem_get state id value')
+    ]
+
+  let st_mem_len state mem_len' = (state === (_, _, mem_len, _))
+
+  let st_add_arg state state_before id arg_tag arg state'' =
+    conde
+    [ (arg_tag === Ref) (arg === RValue) (state'' === state) (* TODO: error *) (* TODO: allow later ?? *)
+    ; (fresh arg') (arg_tag === Ref) (arg === LValue arg')
+      (fresh value') (env_get state_before arg value')
+                     (env_add state id value' state'')
+    ; (arg_tag === Value)
+      (fresh value' state' mem_len_dec')
+      (arg_to_value state_before arg value')
+      (mem_add state value' state')
+      (Nat.succ mem_len_dec' === st_mem_len state)
+      (env_add state' id mem_len_dec' state'')
+    ]
+
+  let st_spoil_assignments state state' =
+    (fresh env mem mem' mem_len assignments)
+    (state === (env, mem, mem_len, assignments))
+    (List.fold_left (fun mem id -> list_replace mem (inv_id mem_len @@ env_get state id) BotV) mem assignments mem')
+    (* TODO: replace with foldlo (or foldro ?) *)
+    (state') === (env, mem', mem_len, [])
+
+  (* --- *)
+
+  let arg_to_lvalue arg arg' = (arg' === LValue arg)
+
+  let rec eval_stmt state prog stmt state' =
+    conde
+    [ (fresh f_id args)
+      (stmt === Call (f_id, args))
+      (fresh f args')
+      (list_nth prog f_id f)
+      (List.mapo arg_to_lvalue args args')
+      (eval_fun state prog f args')
+    ; (fresh id) (stmt === Read id) (mem_check state id state')
+    ; (fresh id) (stmt === Write id) (mem_set state it UnitV state')
+    ]
+
+  and eval_body state prog body state' =
+    (List.fold_left (fun state stmt -> eval_stmt state prog stmt) state body)
+    (* TODO: replace with foldlo (or foldro ?) *)
+
+  and eval_fun state prog decl args state' =
+    (fresh arg_tags body)
+    (fresh env_before mem_before len_before assignments_before)
+    (fresh state_clean)
+    (state_clean === ([], mem_before, len_before, []))
+    (fresh state_with_vars)
+    (state_with_vars === List.fold_left2 (fun (state, id) arg_tag arg -> (st_add_arg state state id arg_tag arg, id + 1)) (state, 0) arg_tags args)
+    (* TODO how, rewrite from scratch ??? *)
+    (* TODO: replace with foldlo (or foldro ?) ?? *)
+    (fresh state_evaled)
+    (eval_body state prog body state_evaled)
+    (fresh state_spoiled)
+    (st_spoil_assignments state_evaled state_spoiled)
+    (fresh mem_updated len_to_drop)
+    (Nat.addo len_to_drop len_before len)
+    (List.drop len_to_drop mem mem_updated)
+    (state' === (env_before, mem_updated, len_before, assignments_before))
+
+  and eval_fun_empty_args state prog decl state' =
+    (fresh arg_tags)
+    (decl === (arg_tags, _))
+    (List.mapo arg_to_rvalue arg_tags args) (* TODO how, rewrite from scratch ??? *)
+    (eval_fun state prog decl args state')
+
+  (* --- *)
+
+  let empty_state state = (state === ([], [], 0, []))
+
+  let eval_prog all_prog state' =
+    (fresh prog main_decl)
+    (all_prog == (prog, main_decl))
+    (eval_fun_empty_args empty_state prog main_decl state')
+end