diff --git a/lib/ast/structures/functions.ml b/lib/ast/structures/functions.ml
index 90924cd..ee1d78e 100644
--- a/lib/ast/structures/functions.ml
+++ b/lib/ast/structures/functions.ml
@@ -36,12 +36,14 @@ module rec Info : sig
   }
 
   (* ---- primitive functions ----- *)
-  val empty  : t 
-  val find   : t -> Id.t -> info
-  val create : int -> t
-  val iter : (Id.t -> info -> unit) -> t -> unit 
+  val empty       : t 
+  val find        : t -> Id.t -> info
+  val find_opt    : t -> Id.t -> info option
+  val create      : int -> t
+  val iter        : (Id.t -> info -> unit) -> t -> unit 
   val add         : t -> Id.t -> Id.t option -> string list -> unit
   val get_func_id : t -> string -> Id.t option -> Id.t option
+  val get_params  : info -> string list 
 
 
 
@@ -60,6 +62,7 @@ end = struct
   let empty = {top_lvl = ref []; functions = FuncTable.create 1}
   let create (size : int) : t = { top_lvl = ref []; functions = FuncTable.create size }
   let find (info : t) : Id.t -> info = FuncTable.find info.functions
+  let find_opt (info : t) : Id.t -> info option = FuncTable.find_opt info.functions
   let replace (info : t) : Id.t -> info -> unit = FuncTable.replace info.functions 
   let remove (info : t) (func_id : Id.t) : unit = 
     let top_lvl = info.top_lvl in 
@@ -111,6 +114,8 @@ end = struct
     (* add found node information to its parent *)
     add_nested info parent_id func_id
 
+  let get_params (info : info) : string list = info.params
+
 end
 
 module Context = struct
@@ -123,27 +128,34 @@ module Context = struct
   let create (functions' : Info.t) : t = { path = []; functions = functions'}
   let visit (context : t) (id : Id.t) : t = {context with path = id :: context.path}
 
-  let get_func_id (context : t) (func_name : string) : Id.t = 
+  let get_func_id (context : t) (func_name : string) : Id.t option = 
     let get_func_info_id = Info.get_func_id context.functions in 
-    let rec aux (path : Id.t list)  : Id.t =
+    let rec aux (path : Id.t list)  : Id.t option =
       let parent_id = hd_opt path in
       let id = get_func_info_id func_name parent_id in 
 
-      if Option.is_some id then Option.get id (* found function nested inside parent id *)
+      if Option.is_some id then id (* found function nested inside parent id *)
       else if Option.is_some parent_id then aux (List.tl path) (* function not found yet but there is more parents to search *)
-      else failwith "function not found" (* function name wasnt found in any parent's nested list *)
+      else None (* function name wasnt found in any parent's nested list *)
 
     in
     aux context.path
 
-  let get_func_info (context : t) (func_name : string) : Info.info = 
+  let get_func_info' (context : t) (func_id : Id.t) : Info.info = 
+    Info.find context.functions func_id
+
+  let get_func_info (context : t) (func_name : string) : Info.info option = 
     let func_id = get_func_id context func_name in 
-    Info.find context.functions func_id 
+    Option.bind func_id (Option.some << get_func_info' context)
 
-  let get_param_names (context : t) (func_name : string) : string list = 
-    let func_info = get_func_info context func_name in 
+  let get_param_names' (contents : t) (func_id : Id.t) : string list = 
+    let func_info = get_func_info' contents func_id in 
     func_info.params
 
+  let get_param_names (context : t) (func_name : string) : string list option = 
+    let func_info = get_func_info context func_name in 
+    Option.map (Info.get_params) func_info
+
   let is_last_definition (context : t) (id : Id.t) : bool =
     let get_func_info_id = Info.get_func_id context.functions in 
     let parent_id = hd_opt context.path in
diff --git a/lib/mdg/analyse.ml b/lib/mdg/analyse.ml
index 8748636..41c4247 100644
--- a/lib/mdg/analyse.ml
+++ b/lib/mdg/analyse.ml
@@ -39,7 +39,7 @@ and analyse (state : state) (statement : m Statement.t) : unit =
   let new_version = Graph.staticNewVersion graph in 
   let new_version' = Graph.dynamicNewVersion graph in 
   let get_param_locs = Graph.get_param_locations graph in
-  let get_param_names = Functions.Context.get_param_names contx in 
+  let get_param_names = Functions.Context.get_param_names' contx in 
   let get_func_id = Functions.Context.get_func_id contx in 
   let is_last_definition = Functions.Context.is_last_definition contx in 
   let visit = Functions.Context.visit contx in 
@@ -128,27 +128,35 @@ and analyse (state : state) (statement : m Statement.t) : unit =
     (* -------- C A L L -------- *)
     | _, AssignNewCall {left; callee; arguments; id_call; id_retn; _}
     | _, AssignFunCall {left; callee; arguments; id_call; id_retn; _} -> 
-      let f = Identifier.get_name callee in 
       let _Lss = List.map eval_expr arguments in 
       let l_call = alloc id_call in 
+      let l_retn = alloc id_retn in 
+
+      (* get function definition information *)
+      let f    = Identifier.get_name callee in 
+      let f_id = get_func_id f in 
+
+      (* node information *)
+      add_node l_call (f ^ "()");
+      add_node l_retn (Identifier.get_name left);
+      
       (* argument edges *)
-      let params = get_param_names f in 
+      let params = map_default get_param_names [] f_id in 
       List.iteri ( fun i _Ls -> 
-        let param_name = List.nth params i in 
+        let param_name = Option.value (List.nth_opt params i) ~default:"undefined" in 
         LocationSet.iter (fun l -> add_arg_edge l l_call i param_name) _Ls
       ) _Lss;
-      
-      (* call edge *)
-      let l_f = Graph.get_func_node graph (get_func_id f) in 
-      add_call_edge l_call (Option.get l_f);
-      add_node l_call (f ^ "()");
 
-      (* add return edge *)
-      let l_retn = alloc id_retn in 
+      (* return edge *)
       add_ret_edge l_call l_retn;
-      add_node l_retn (Identifier.get_name left);
       store_update left (LocationSet.singleton l_retn);
 
+      (* call edge to function definition (if defined) *)
+      option_may (fun id ->
+        let l_f = Graph.get_func_node graph id in 
+        add_call_edge l_call (Option.get l_f)
+      ) f_id;
+
     (* -------- I F -------- *)
     | _, If {consequent; alternate; _} ->
       let state' = State.copy state in 
diff --git a/lib/mdg/structures/graph'.ml b/lib/mdg/structures/graph'.ml
index 3ecaf5d..9ca2098 100644
--- a/lib/mdg/structures/graph'.ml
+++ b/lib/mdg/structures/graph'.ml
@@ -180,7 +180,7 @@ let iter (f : location -> EdgeSet.t -> Node.t option -> unit) (graph : t) = Hash
 
 (* ------- A U X I L I A R Y   F U N C T I O N S -------*)
 let get_edges (graph : t) (origin : location) : EdgeSet.t = 
-  map_default identity EdgeSet.empty (find_edges_opt graph origin)
+  Option.value (find_edges_opt graph origin) ~default:EdgeSet.empty
 
 let is_version_edge (_to : location) (edge : Edge.t) : bool = Edge.is_version edge && Edge.get_to edge = _to
 
diff --git a/lib/mdg/structures/store.ml b/lib/mdg/structures/store.ml
index 40ed0fc..5440bf9 100644
--- a/lib/mdg/structures/store.ml
+++ b/lib/mdg/structures/store.ml
@@ -1,8 +1,6 @@
 open Structures
 open Ast.Grammar
 open Auxiliary.Structures
-open Auxiliary.Functions
-
 
 type t = LocationSet.t HashTable.t
 
@@ -31,7 +29,7 @@ let equal (store : t) (store' : t) : bool = HashTable.equals (LocationSet.equal)
 
 (* ------- A U X I L I A R Y   F U N C T I O N S -------*)
 let get_locations (store : t) (id : location) : LocationSet.t =
-  map_default identity LocationSet.empty (find_opt store id)
+  Option.value (find_opt store id) ~default:LocationSet.empty
   
 (* ------- S T O R E   M A N I P U L A T I O N ------- *)
 let get (store : t) ((_, {name; _}) : m Identifier.t) : LocationSet.t =