Tim Chevalier wrote:
On 8/14/08, Roman Leshchinskiy <[EMAIL PROTECTED]> wrote:
IIUC, the practical difference is this. If you have
f :: Int -> (# Int #)
then
case f m of (# n #) -> bar n
will call f before calling bar but will not evaluate n.
I fear I'm still not enlightened. I see how your example works, but in
the particular context where GHC introduces these singleton tuples,
the tuple will contain an unboxed value (the result of a foreign
function call.) So if n is unboxed, isn't
case f m of (# n #) -> bar n
exactly equivalent to
bar $! (f m)
?
Yes - in the case where the value is unboxed (or unlifted), it makes no
difference to wrap it in a singleton unboxed tuple. I actually have no
idea why we use (# State# RealWorld #) rather than just State# RealWorld in
that case. Perhaps we could just change it, because the return convention
is the same in both cases.
Cheers,
Simon
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