Donald Bruce Stewart wrote:
Ha! I don't think "pure lazy fp" would be the phrase I would choose to
describe this code.
An example (from fannkuch):
t <- IO $ \s ->
case readIntOffAddr# p1# 0# s of
(# s, p1 #) -> case readIntOffAddr# p1# (n# -# 1#) s of
(# s, pn #) -> (# s, not (p1 ==# 0# || pn ==# (n# -# 1#)) #)
Ok, I'll bite ;) This is a very atypical "example", as fannkuch is the
only entry written this way (and it could be rewritten, with careful
> attention to the Core). There are also many lovely pure, lazy entries.
Not so atypical.
More examples (I didn't look /that/ hard.. :))
-----------------------------------
* From reverse-complement
reverseit iubc strand i l s =
if i >=# l
then (# s, (I# i, I# l) #)
else case readWord8OffAddr# strand i s of { (# s, c #) ->
case readWord8OffAddr# strand l s of { (# s, x #) ->
case readWord8OffAddr# iubc (word2Int# x) s of { (# s, y#)
[snip]
* From k-nucleotide.
eqmem i ptr1 ptr2 s = if i ==# 0# then (# s , True #) else
case readInt8OffAddr# ptr1 0# s of { (# s, i8a #) ->
case readInt8OffAddr# ptr2 0# s of { (# s, i8b #) ->
if i8a ==# i8b
then eqmem (i -# 1#) (plusAddr# ptr1 1#) (plusAddr# ptr2 1#) s
else (# s, False #) } }
* From n-body.
kineticE i = let i' = (.|. (shiftL i 3))
in do m <- mass i
vx <- unsafeRead b (i' vx)
vy <- unsafeRead b (i' vy)
vz <- unsafeRead b (i' vz)
return $! 0.5 * m * (vx*vx + vy*vy + vz*vz)
----------------------
*I* am certainly not implying that Haskell is anything less than the
most wonderous language in the entire world.
I'm saying that there's a stark difference in style between the programs
submitted to the shootout, and the ones I would show to people that I
myself was trying to introduce to the wonders of purely lazy functional
programming. :).
I think there's a big-fat-lesson about the tension between abstraction
and implementation in these entries.
On one hand we've got "This is what I want", on the other it's "What do
I have to do to implement it".
Ben.
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