Function colouring created a lot of angst when it first came about, particularly because of the difficulties of calling a function of one colour from another. W

Function colouring created a lot of angst when it first came about, particularly because of the difficulties of calling a function of one colour from another. Whether that was possible, what it actually meant, wasn't really well defined. As other comments have said, there's nothing special about "colouring"; sync/async functions are a case where those above problems are tough, but simpler versions of the problem are everywhere and we don't freak out about them e.g. call a fallible function from an infallible function. It really all turns on how easy it is to ultimately make the call to the other "function" colour. In Zig's case, if its easy to get an Io in a function that didn't take an Io, it's a non-issue. Likewise for the "fallible function call from infallible function": if it fails, do something that doesn't result in the infallible function failing (do something else? Terminate? Anything will do).