31 Jul
2010
31 Jul
'10
1:47 p.m.
On Sat, Jul 31, 2010 at 5:59 PM, michael rice
OK, in f, *length* already knows it's argument is a list.
In g, *length* doesn't know what's inside the parens, extra evaluation there. So g is already ahead before we get to what's inside the [] and ().
According to the types, we already know both are lists. The question is, of course, what kind of list.
But since both still have eval x to *thunk* : *thunk*, g evaluates "to a deeper level?"
Michael
I think this question is being quite sneaky. The use of head and tail is pretty much irrelevant. Try the pointfree versions: f = length . (:[]) . head g = length . tail and see if that helps you see why f is lazier than g.