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
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