[Haskell-cafe] Why is Bool no instance of Num and Bits?
ndmitchell at gmail.com
Fri May 8 12:04:54 EDT 2009
> Does that also mean that you could write:
> if 3 - 4 then ... else ... (= if (fromInteger 3 :: Bool) - (fromInteger 4
> :: Bool) then ... else ...)
No. 3 - 4 is an Integer, the proposal is to convert Bools to Ints, not
Ints to Bools. Of course, Lennart has been asking for precisely this
functionality (overloaded Booleans) for some time - so one day it may
You could however do:
if 3 then ... else ..
> If you change fromInteger in Num Bool to be fromInteger x = x /= 0, then we
> could all start writing nasty C-like if-expressions...
Yeah, the more people give examples of the power of Num Bool, the more
it seems like a very bad idea!
Which is a shame, having Bits on Bool seems entirely logical, having
Num a superclass of Bits seems a little less clear.
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