Truncator for funs; special case binary truncation when max is 0

src/trunc_io.erl

@@ -172,6 +172,9 @@ print(Atom, _Max) when is_atom(Atom) ->
 print(<<>>, _Max) ->
     {"<<>>", 4};
 
+print(Binary, 0) when is_binary(Binary) ->
+    {"<<..>>", 6};
+
 print(Binary, Max) when is_binary(Binary) ->
     B = binary_to_list(Binary, 1, lists:min([Max, size(Binary)])),
     {L, Len} = alist_start(B, Max-4),
@@ -181,9 +184,16 @@ print(Float, _Max) when is_float(Float) ->
     L = float_to_list(Float),
     {L, length(L)};
 
-print(Fun, _Max) when is_function(Fun) ->
+print(Fun, Max) when is_function(Fun) ->
     L = erlang:fun_to_list(Fun),
-    {L, length(L)};
+    case length(L) > Max of
+        true ->
+            S = erlang:max(5, Max),
+            Res = string:substr(L, 1, S) ++ "..>",
+            {Res, length(Res)};
+        _ ->
+            {L, length(L)}
+    end;
 
 print(Integer, _Max) when is_integer(Integer) ->
     L = integer_to_list(Integer),

test/trunc_io_eqc.erl

@@ -115,7 +115,7 @@ gen_fun() ->
 prop_format() ->
     ?FORALL({FmtArgs, MaxLen}, {gen_fmt_args(), gen_max_len()},
             begin
-                FudgeLen = 31, %% trunc_io does not correctly calc safe size of pid/port/numbers
+                FudgeLen = 31, %% trunc_io does not correctly calc safe size of pid/port/numbers/funs
                 {FmtStr, Args} = build_fmt_args(FmtArgs),
                 try
                     Str = lists:flatten(trunc_io:format(FmtStr, Args, MaxLen)),