Q: Forcing repeated evaluation

[Jan Kybic]

Hello,
        I have another question regarding the optimisation of Haskell code:
I have a relatively inexpensive function generating a long list, imagine
something like (I simplified a lot):

l = [ i*i*i | i <- [0..n] ]   -- for very large n

This long list is consumed several times in the program:

x1 = f1 l
x2 = f2 x1 l
x3 = f3 x2 l

I found that the list l is calculated just once and that the
computational time is dominated by the allocations and garbage
collection. I want to try to force l to be generated on-the-fly
every time it is needed, to see if it improves performance.
What is a good way to do it? Would something like

unsafePerformIO $ return l

do the job? Isn'it there any flag for the compiler (ghc) to suggest
this optimisation? Thank you for your feedback.

Jan

-- 
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Jan Kybic <kybic@ieee.org>      Odyssee, INRIA, Sophia-Antipolis, France
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