Am Samstag, 9. Februar 2008 17:33 schrieb Peter Verswyvelen:
Consider the function
cond x y z = if x then y else z
I guess we can certainly say cond is strict in x.
But what about y and z?
If x is true, then cond is strict in y If x is false, then cond is strict in z
So we can't really say cond is lazy nor strict in its second or third argument.
Of course, this is the case for many more functions, but in the case of the if-then-else primitive, does the strictness analyzer make use of this "mutually exclusive strictness" fact?
Cheers, Peter
Hope I remember correctly... A function is strict in an argument, if whenever that argument is _|_, the result is _|_, regardless of possible other arguments. Since if True then 0 else _|_ == 0, if-then-else is nonstrict in the third argument, similarly if False then _|_ else 0 == 0, so if-then-else is nonstrict in the second argument. Cheers, Daniel