The point is that it's valid syntax (invalid syntax is found in an earlier phase of compilation and would report much faster). It's invalid in Swift's type system, and it takes it 42 seconds (in the string example) and 8 seconds (in the math expression one) for it to tell you that it can't type-check it in a reasonable time and then it quits.

That’s the point. It’s invalid swift syntax, but it takes >40 seconds to tell you that.

If there was just the right overload hiding somewhere, it wouldn't be an error and it would take a similar amount of time. This is just the easiest way to show off the problem, which is how long it takes to check.