Assign-and-compare in go's while-equivalent?

In Go you can do: ``` if foo := bar() ; foo != nil { ... } ``` In C/C++ you can do: ``` while ((foo = bar()) != NULL) { ... } ``` However, Go's syntax does not seem to provide any equivalent way of doing assign-and-compare in a while loop; Go has replaced `while` with a specific invocation of `for` (e.g. `for a` is equivalent to `for ; a ;`). Simply trying to use the `if` version syntax confuses the parser, as it's expecting there to be a third statement. I could just say: ``` for foo := bar() ; foo != nil ; foo = bar() { .... } ``` but in this case, the `bar()` call is fairly long, complex, and not easy to break out into its own function (although I could do something like declaring a local `func` to call, but that still reduces the clarity of the code). For now I am doing: ``` for { foo := bar(); if foo == nil { break; } ... } ``` but this seems unclean, both because it separates the loop criteria from the loop statement itself, and because it relies on `break`. So, is there a clean, idiomatic way of doing an assign-and-compare in a while loop in Go? This is such a common use case I can't imagine that there's no way of doing it.