better error message for the ai command

testsuite/runtime/typecheck/typecheck.gfs.gold

@@ -7,10 +7,7 @@ A function type is expected for the expression 1 instead of type Int
 Couldn't match expected type Int -> Int␍
        against inferred type Int␍
 In the expression: 1␍
-␍
-␍
-Function unknown_fun is not in scope␍
-␍
+unknown category of function identifier unknown_fun␍
 ␍
 Category unknown_cat is not in scope␍
 Cannot infer the type of expression \x -> x␍