Jan Kybic wrote:
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
A simple solution is to "decaf" the offending definition. Give l an argument of trivial type: replace l both in its definition and at all point of use by the application l ().