In 6.4, minimum & maximum will have specialised versions for Int & Integer, which will run in constant stack space. We can't do this in general, because minimum/maximum have the type (Ord a) => [a] -> a and we can't assume that the comparison operations for any given type are always strict. Cheers, Simon On 10 September 2004 12:17, Serge D. Mechveliani wrote:
See my next letter -- about compiling of minimum [1 .. (10^6)] with -O. Because, I think, [1 .. (10^6)] is a program which interferes with `minimum', and it depends much on how cleverly this whole expression is complied, for example, `minimum' is in-lined or not.
Probably, `minimum' can be rewritten so, that the whole thing will reliably perform in a constant space in the interpreter mode too.
And maybe it is, generally, hard to optimize reliably foldl.
----------------- Serge Mechveliani mechel@botik.ru
On Fri, Sep 10, 2004 at 12:29:01PM +0200, Jerzy Karczmarczuk wrote:
Serge D. Mechveliani wrote:
The library functions like minimum, maximum, should perform in a constant space: probably, it is easy to write them his way. And ghc-6.2.2-pre shows
Prelude> minimum [1 .. (10^4)] 1
Prelude> minimum [1 .. (10^6)]
*** Exception: stack overflow Prelude>
What do you think of this, please?
Strange, I thought that foldl or foldl1 don't produce such garbage here. I tested with Hugs, you are right also here, this is not specific to GHC.
minim (x:l) = mi x l where mi x (y:q) |x
This one works. But it is brutal, not so exquisite...
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