The problem with effects systems is that effects aren't generalisable. Every effect is unique. Sometimes they can be applied automatically and sometimes not. Y

The problem with effects systems is that effects aren't generalisable. Every effect is unique. Sometimes they can be applied automatically and sometimes not. You can have the compiler automatically recompile map with async to make map<async>, likewise map<pure> and map<nofail> and map<noblock> but they will not be optimal; map<async> could be parallel but isn't. And you probably want to control the amount of parallelism at each call site, which just makes it a completely different function. It's likely that you wrote map in a way that uses a loop counter and it's possible the compiler can't prove it's pure. map<abortable> is likely correct, but the compiler has absolutely no way to prove that, and other functions won't be correct if you naively make them possible to abort from outside.