Good point. For this case, it's easy to imagine - such a construct would infer the function's new return type, and then any call-sites which have a mismatch wou

Good point. For this case, it's easy to imagine - such a construct would infer the function's new return type, and then any call-sites which have a mismatch would require updating. But you raise the real question of how the compiler could know when types were added by the inference-er versus the programmer