Hello! On Fri, Mar 08, 2002 at 12:52:58AM -0300, Andre W B Furtado wrote:
Another question about labelled types, this time concerning about efficiency: is there any efficiency differences between functions f and g below?
data RType = R Int Char data Stype = S {x :: Int, y :: Char}
f :: RType -> Int f (R x _) = x
g :: SType -> Int g s = x s
Thanks again, -- Andre
In principle, the representation of RType and Stype is the same. The only difference of Stype over RType is the implicit definition of the functions (accessors) x and y, as well as the syntactic sugar for constructing values, pattern matching and functional update using field names. But as said, that's just functional sugar and should be just exactly as efficient as using the manual translation of those constructs on RType. Now, that said, g *looks* a bit more lazy than f, as in f, you don't evaluate the right side if the parameter isn't R _|_ _|_ or more. However, I said *looks*, but if one checkes, it's thus, desugared: f (R x _) = x g s = x s where x (S xElem _yElem) = xElem And if you just evaluate both at _|_, the result is _|_ for both f and g. So in fact, there equally strict. Finally, the code for f and g should, save for renaming, be just the same. Kind regards, Hannah.