@@ -1,14 +1,13 @@
 @@type = fun(x){
   if _isint(x): "int"
   else if _isstr(x): "str" 
-  else if _isundefined(x): "undefined"
   else: "any"
 };
 
 def binop(a,b,c) {
   fun(x,y){@value(
-    if( @type(x)=="undefined" || @type(y)=="undefined" ) then "undefined" else
+    if( _isbot( @type(x) ) || _isbot( @type(y) ) ) then @type(...) else
       if( @type(x)==a && @type(y)==b ) then c else "error"
   )}
 };
 
@@ -17,9 +16,9 @@
 @type "<" = binop("int", "int", "int");
 @type ">" = binop("int", "int", "int");
 
 def mergeType(a,b) {
-  if( a == "undefined" ): ( if(b=="undefined"):"error" else b  ) else ( a )
+  if( _isbot(a) ): ( if( _isbot(b) ):"error" else b  ) else ( a )
 };
 
 @type "if" = fun(c,t,e) {@value(
  if(@type(c)=="int" ): mergeType(@type(t()), @type(e())) else : "error"