On Mar 29, 2006, at 2:23 PM, Andy Gill wrote:
John, et. al.,
I'd rather just use a polymorphic function, but would having some
sort of ... notation in class contexts help?
sort (Eq a,_) => [a] -> [a]
Which means that we need at least the Eq a, but perhaps more.
See #86 http://hackage.haskell.org/trac/haskell-prime/wiki/
PartialTypeAnnotations
In terms of seq, and deepSeq, here is a space leak problem I often
need to solve.
Imagine a function
cpuStep :: CPUState -> CPUState
where the CPUState is a large structure, for (say) the 68000
register file, a
and also contains information about a level-1 cache.
I want to run for 100,000 instructions.
runCPU :: Int -> CPUState -> CPUState
runCPU 0 state = state
runCPU n state = runCPU (n-1) (cpuStep state)
My job is to make this run in approximately constant space; a
reasonable request.
Well, we can add a seq to the modified state:
runCPU n state = state'` `seq` runCPU (n-1) state'
where
state' = cpuStep state
But the thing still leaks like crazy. *I've seen this again and
again.*
Some internal piece of data inside CPUState depends on
the value of another piece of CPUState from the previous
iteration.
[snip]
Questions
- Does anyone have any better suggestions of how to fix this real
issue?
My initial thought is to add strictness flags to the datatype
declaration for the bits of state that cause trouble (report, section
4.2.1). For something like this, I'd expect you could safely mark
_every_ field strict; in that case you might be able to coerce the
compiler to unbox the entire state record and save a few allocations.
But it strikes me that you must have thought of this already; is
there some reason it won't work?
[snip]
Rob Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
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