Re: [Haskell-cafe] Why does this blow the stack?

dbenbenn:

On Dec 21, 2007 12:02 PM, Don Stewart wrote:

...

There's no good reason for the accumulator for Integer to be lazy, especially when you see that adding an upper bound (enumFromTo) or using Int uses a strict accumulator.

I've filled a bug report and fix for this.

http://hackage.haskell.org/trac/ghc/ticket/1997

there's an ad hoc sprinkling of strict and lazy Num ops for Integer through the base library, while Int is fairly consistently strict.

Thanks for fixing this. But doesn't GHC have strictness analysis?

Sure does!

Even if there was consistent strictness for Integer in the base library, that wouldn't help for code not in the base library. In other words, I want to be able to define

mysum :: (Num a) => [a] -> a mysum = foldl (+) 0

in my own programs, and have GHC automatically make it strict if "a" happens to be Int or Integer. Is there any chance of GHC getting that ability?

Thankfully, GHC does that already :) mysum :: (Num a) => [a] -> a mysum = foldl (+) 0 main = print (mysum [1..10000000]) In ghc 6.6, $ time ./A +RTS -M20M Heap exhausted; Current maximum heap size is 19996672 bytes (19 Mb); use `+RTS -M<size>' to increase it. and in GHC 6.8, ghc can see through to the strictness of (+) $ time ./A +RTS -M20M 50000005000000 ./A +RTS -M20M 0.95s user 0.00s system 99% cpu 0.959 total The problem here was an explicit recusive loop though, with just not enough for the strictness analyser to get going. -- Don