Chris Kuklewicz wrote:
Weak uses seq to achieve WHNF for it's argument
newtype Weak a = WeakCon {runWeak :: a} mkWeak x = seq x (WeakCon x) unsafeMkWeak x = WeakCon x
This doesn't actually do what you think it does. mkWeak and unsafeMkWeak are the same function. mkWeak 123 = seq 123 (WeakCon 123) = WeakCon 123 unsafeMkWeak 123 = WeakCon 123 mkWeak _|_ = seq _|_ (WeakCon _|_) = _|_ unsafeMkWeak _|_ = WeakCon _|_ = _|_ To quote John Meacham: | A quick note, | x `seq` x | is always exactly equivalant to x. the reason being that your seq | would never be called to force x unless x was needed anyway. | | I only mention it because for some reason this realization did not hit | me for a long time and once it did a zen-like understanding of seq | (relative to the random placement and guessing method I had used | previously) suddenly was bestowed upon me. I remember this anecdote because when I first read it, a zen-like understanding of seq suddenly was bestowed upon /me/. Maybe it should be in the docs. :-) -- Ben