Jules Bean wrote:
On 10 Dec 2004, at 15:34, Robert Dockins wrote:
So it should get "flattened," but it still doesn't run in constant
space because the "x" parmeter isn't strict, so it will accumulate a
bunch of closures like (((((((0)+1)+1)+1)+1)+1).... To make it strict,
do something like this:
Isn't this what the strictness analyser is for? Doesn't GHC know that +
for Int is strict in both arguments, and therefore it shouldn't
accumulate a great big thunk like that?
Jules
Doesn't look like....
-------------- cnt.hs ------------------------
countlines = aux 0
where aux x [] = x
aux x (_:ls) = aux (x+1) ls
countlines' = aux 0
where aux x [] = x
aux x (_:ls)
| x `seq` False = undefined
| otherwise = aux (x+1) ls
-----------------------------------------------
$ /cygdrive/c/ghc/ghc-6.2.2/bin/ghci.exe
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.2.2, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base ... linking ... done.
Prelude> :load cnt.hs
Compiling Main ( cnt.hs, interpreted )
Ok, modules loaded: Main.
*Main> countlines [1..100000]
100000
*Main> countlines [1..1000000]
*** Exception: stack overflow
*Main> countlines' [1..1000000]
1000000
*Main>
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