Re: [Haskell-cafe] 1 = 0?

On Tue, Jun 17, 2014 at 12:51 PM, Roman Cheplyaka wrote:

* Alexey Muranov [2014-06-17 03:25:10-0700]

...

Is this the expected behavior that

1 = 0

does not raise any error? What does this mean?

1 is a valid (nullary) pattern, so yes. This pattern binding obviously fails.

Prelude> let x@1 = 0 Prelude> x *** Exception: <interactive>:2:5-11: Irrefutable pattern failed for pattern x@1

It doesn't even have to fail, since numeric literals are overloaded: instance Num () where fromInteger _ = () v :: () v = let x@1 = 0 in x

v ()

Erik