Am Freitag, 26. März 2004 13:30 schrieb Keith Wansbrough:
Does the bias matter at all if Eq means equality?
It should be documented, so "advanced users" can rely on the behaviour.
In my opinion, even "advanced users" should adhere to The Haskell Report which says that (==) means equality.
Sorry, not sure what happened with my previous reply. Here it is again:
data Foo = Foo Int Int
instance Eq Foo where (Foo x _) == (Foo y _) = x == y
mkFoo x = Foo x (expensive_calculation x) fooX (Foo x _) = x fooY (Foo _ y) = y
a = mkFoo 10 b = mkFoo 10 =
m = if fooY a > 10 then add a empty else empty m' = add b m
Now it would be nice to know that a is in the collection, not b, because a's Y component has been forced, but b's hasn't. Replacing a with b would waste work.
Thus knowing the bias may be important for time/space analysis.
--KW 8-)
Ok, you're right. But a bias specification should not be needed to know what the result of the add function is semantically. A bias spec is, of course, needed for Map.add. Wolfgang