adding alpha conversion

lambda/lambda.ml

@@ -29,6 +29,25 @@ let rec beta = function
   | App (Lambda (x, t), u) -> subst t [(x, u)]
   | _ -> failwith  "This term is not a redex"
 
+(* return i where i is the smallest suffix needed so that "x ^ i"  isn't in l *)
+let rec var_counter i x l = 
+  if List.mem (x ^ (string_of_int i)) l then var_counter (i+1) x l 
+  else i
+
+(* Alpha Conversion : renames lambda variables duplicates by adding a number to them*)
+let alpha_conv t =
+  let rec aux l = function
+  | Var x when List.mem x l -> 
+      let i = string_of_int ( (var_counter 0 x l) - 1) in 
+      if i = "-1" then Var x
+      else Var (x^i)
+  | Var x -> Var x
+  | Lambda(x, t) when List.mem x l -> 
+      let i = string_of_int (var_counter 0 x l) in 
+      Lambda (x^i, aux ((x^i)::l) t)
+  | Lambda(x, t) -> Lambda (x, aux (x::l) t)
+  | App (t, u) -> App (aux l t, aux l u)
+  in aux [] t
 (* ---------------------------------------
    Exemples
    --------------------------------------- *)
@@ -145,3 +164,5 @@ let rec cbn = function
 let rec cbn_eval t = 
   try let t' = cbv t in
     cbn_eval t' with Irreductible -> t 
+
+

lambda/main.ml

@@ -49,6 +49,12 @@ let _ =
 				let t = termc Lexer.read lexbuf in
 				print_endline (string_of_term t)
 			with _ -> print_endline "Syntax error. Please try again.")
+		| "alpha"::string_list -> 
+			let lexbuf = Lexing.from_string (String.concat " " string_list) in
+			(try 
+				let t = termc Lexer.read lexbuf in
+				print_endline (string_of_term (alpha_conv t))
+			with _ -> print_endline "Syntax error. Please try again.")
 		| ["cbn"; "-f"; filename] ->
 			begin try
 				let lexbuf = Lexing.from_channel (open_in filename) in