part of function coloring is "not being trivially resolvable". in this case the function coloring boundary is trivially resolvable. const pick_a_global_io

part of function coloring is "not being trivially resolvable". in this case the function coloring boundary is trivially resolvable. const pick_a_global_io = ...; fn needs_io(io:IO) void {...} fn doesnt_take_io() void { needs_io(pick_a_global_io); } easy peasy. you've resolved the coloring boundary. now, if you want to be a library writer, yeah, you have to color your functions if you don't want to be an asshole, but for the 95% use case this is not function coloring.