"Rijk J. C. van Haaften" <[EMAIL PROTECTED]> wrote: > Recently, I wrote a function similar to > > x :: a > x = x 42 > > which is type-correct (Hugs, Ghc, THIH). > Still, from the expression it is clear > that the type shoud have a function type. > The definition > > x :: a -> b > x = x 42 > > is equally well accepted, though I can't > see why this type would be correct. (I'd > expect it to be too general.) > > For what reasons are these types considered > correct?
When you say x :: a you are asking that the compiler check that everything you say about x is consistent with x being acceptable where /any/ type is required. In the application x 42, it requires that x be a function, which is fine, because x has any type, and this includes functions. When you say x = x 42, this requires that the type returned from x 42 is the same as the type of x, again fine because if x::a, then x:: Integer -> a also, so x 42:: a. It works out in practise because x = x 42 gives x the value bottom, and bottom::a for all a. Jón -- Jón Fairbairn [EMAIL PROTECTED] 31 Chalmers Road [EMAIL PROTECTED] Cambridge CB1 3SZ +44 1223 570179 (after 14:00 only, please!) _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
