On Mon, Feb 2, 2015 at 5:07 PM, Paul Rubin <no.email@nospam.invalid> wrote: > Chris Angelico <ros...@gmail.com> writes: >> So since you can set something to Nothing regardless of type, and >> compare it against Nothing regardless of type, it doesn't really much >> matter that there are different types of Nothing. Right? > > No that's not how type inference works. If you have x = Nothing and > pass it to a function that takes a Maybe Int, type inference means the > compiler figures out that x must have type Maybe Int. If you then also > pass x to something that takes Maybe String, you are telling the > compiler that x has two different types at the same time, so the > compiler reports a type error.
If you say "x = 5" and pass it to a function that accepts "Int or String", the compiler knows that it's actually an Int. If you then also pass that x to something that takes "Int or List", is that legal? If so, then 5 is separate from the "or String" and "or List" parts, and Nothing is actually typed. If not, then it's x, not Nothing, that has the type. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
