diff --git a/src/simulation.ml b/src/simulation.ml
new file mode 100644
index 0000000..716f133
--- /dev/null
+++ b/src/simulation.ml
@@ -0,0 +1,92 @@
+open Ast
+
+type sim_var =
+  | SIVar of ident * (int option)
+  | SBVar of ident * (bool option)
+  | SRVar of ident * (real option)
+
+type sim_node_st =
+  {
+    node_outputs: sim_var list;
+    node_loc_vars: sim_var list;
+    node_inner_nodes: sim_node list;
+  }
+and sim_node_step_fn =
+  sim_node_st -> sim_var list -> (sim_var list * sim_node_st)
+and sim_node = sim_node_st * sim_node_step_fn
+
+let pp_sim fmt ((sn, _): sim_node) =
+  let rec aux fmt vars =
+    match vars with
+    | [] -> ()
+    | SIVar (s, None) :: t ->
+        Format.fprintf fmt "\t<%s : int> uninitialized yet.\n%a" s aux t
+    | SBVar (s, None) :: t ->
+        Format.fprintf fmt "\t<%s : bool> uninitialized yet.\n%a" s aux t
+    | SRVar (s, None) :: t ->
+        Format.fprintf fmt "\t<%s : real> uninitialized yet.\n%a" s aux t
+    | SIVar (s, Some i) :: t ->
+        Format.fprintf fmt "\t<%s : real> = %d\n%a" s i aux t
+    | SBVar (s, Some b) :: t ->
+        Format.fprintf fmt "\t<%s : real> = %s\n%a" s (Bool.to_string b) aux t
+    | SRVar (s, Some r) :: t ->
+        Format.fprintf fmt "\t<%s : real> = %f\n%a" s r aux t
+  in
+  if sn.node_loc_vars <> []
+    then
+      Format.fprintf fmt "State of the simulated node:\n\
+                          \tOutput variables:\n%a
+                          \tLocal variables:\n%a"
+        aux sn.node_outputs
+        aux sn.node_loc_vars
+    else
+      Format.fprintf fmt "State of the simulated node:\n\
+                          \tOutput variables:\n%a
+                          \tThere are no local variables:\n"
+        aux sn.node_outputs
+
+
+exception MySimulationException of string
+
+let fetch_node (p: t_nodelist) (s: ident) : t_node =
+  match List.filter (fun n -> n.n_name = s) p with
+  | [e] -> e
+  | _ -> raise (MySimulationException (Format.asprintf "Node %s undefined." s))
+
+let fetch_var (l: sim_var list) (s: ident) =
+  match List.filter
+    (function
+      | SBVar (v, _) | SRVar (v, _) | SIVar (v, _) -> v = s) l with
+  | [v] -> v
+  | _ -> raise (MySimulationException
+                (Format.asprintf "Variable %s undefined." s))
+
+(** TODO! *)
+let make_sim (main_fn: ident) (p: t_nodelist): sim_node =
+  let main_n = fetch_node p main_fn in
+  let node_outputs =
+    List.map
+      (function
+        | IVar s -> SIVar (s, None)
+        | BVar s -> SBVar (s, None)
+        | RVar s -> SRVar (s, None))
+      (snd main_n.n_outputs) in
+  let node_loc_vars: sim_var list =
+    List.map
+      (function
+        | IVar s -> SIVar (s, None)
+        | BVar s -> SBVar (s, None)
+        | RVar s -> SRVar (s, None))
+      (snd main_n.n_local_vars) in
+  let node_inner_nodes = (* TODO! *) [] in
+  ({node_outputs = node_outputs;
+    node_loc_vars = node_loc_vars;
+    node_inner_nodes = node_inner_nodes; },
+    (fun s l -> (s.node_outputs, s)))
+
+
+
+let simulate main_fn ast =
+  let sim_ast = make_sim main_fn ast in
+  Format.printf "Initial state:\n%a" pp_sim sim_ast
+