Add TCO support for reversed branches

src/interpreter.ml

@@ -344,7 +344,7 @@ struct
         let table' = ref table in
         let b t = match (evalExp cond_exp t depth) with
           VAL [] -> false
-          | VAL _ -> (*print_string (printVal (snd (List.hd_exn (List.tl_exn t)))); *) true
+          | VAL _ -> true
           | _ -> raise (RunError ("illegal arg to if", p)) in
         let () = while b !table' do
           table' := (List.fold (List.zip_exn params arg_exps) ~init:[] ~f:(fun l e ->

src/syntax.ml

@@ -136,11 +136,15 @@ struct
     | Comp (exp, s1, s2, pos) -> string_of_exp exp
 
   let optimize_tco (prog: program): program =
+    let names_equal s1 s2 = Int.equal 0 (String.compare s1 s2) in
     let decls, e = prog in
     let decls' = List.map decls ~f:(fun (name, decl) ->
         match decl with
-          Func (params, IF (condition_exp, CALL (fn_name, arg_exps, _), else_exp, p1), p2) when Int.equal 0 (String.compare name fn_name) ->
+          Func (params, IF (condition_exp, CALL (fn_name, arg_exps, _), else_exp, p1), p2) when names_equal name fn_name ->
           (name, Func (params, LOOP (arg_exps, condition_exp, else_exp, params, p1), p2))
+        | Func (params, IF (condition_exp, then_exp, CALL (fn_name, arg_exps, _), p1), p2) when names_equal name fn_name ->
+          let inverse_condition = IF (condition_exp, EMPTY, NUM (1, p2), p2) in
+          (name, Func (params, LOOP (arg_exps, inverse_condition, then_exp, params, p1), p2))
         | d -> (name, d)
       ) in
     (decls', e)