Re: [Haskell-cafe] 1 = 0?

2014-06-17 12:51 GMT+02:00 Roman Cheplyaka :

* 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

If it can make things clearer, you can do something similar with any constructor: > let Just x = Just 5 in x > let Just x = Nothing in x *** Exception: <interactive>:19:5-20: Irrefutable pattern failed for pattern Data.Maybe.Just x