Re: Primitive types and Prelude shenanigans

On 21-Feb-2001, Marcin 'Qrczak' Kowalczyk wrote:

Wed, 21 Feb 2001 12:55:37 +1100, Fergus Henderson pisze:

...

The documentation in the Haskell report does not say what `fromInteger' should do for `Int', but the Hugs behaviour definitely seems preferable, IMHO.

Sometimes yes. But for playing with Word8, Int8, CChar etc. it's sometimes needed to just cast bits without overflow checking, to convert between "signed bytes" and "unsigned bytes".

Both are desirable in different situations. But if you want to ignore overflow, you should have to say so explicitly. `fromInteger' is implicitly applied to literals, and implicit truncation is dangerous, so `fromInteger' should not truncate. There should be a different function for conversions that silently truncate. You can implement such a function yourself, of course, e.g. as follows: trunc :: (Bounded a, Integral a) => Integer -> a trunc x = res where min, max, size, modulus, result :: Integer min = toInteger (minBound `asTypeOf` res) max = toInteger (maxBound `asTypeOf` res) size = max - min + 1 modulus = x `mod` size result = if modulus > max then modulus - size else modulus res = fromInteger result But it is probably worth including something like this in the standard library, perhaps as a type class method. -- Fergus Henderson | "I have always known that the pursuit | of excellence is a lethal habit" WWW: http://www.cs.mu.oz.au/~fjh | -- the last words of T. S. Garp.