Does Haskell optimizer utilize memoization for repeated function calls in a scope?

Question

Consider this function:

f as = if length as > 100 then length as else 100

Since the function is pure it\'s obvious that the length will

Answer 1

GHC now does some CSE by default, as the -fcse flag is on.

On by default.. Enables the common-sub-expression elimination optimisation. Switching this off can be useful if you have some unsafePerformIO expressions that you don't want commoned-up.

However, it is conservative, due to the problems with introducing sharing (and thus space leaks). The CSE pass is getting a bit better though (and this).

Finally, note there is a plugin for full CSE.

• http://hackage.haskell.org/package/cse-ghc-plugin

If you have code that could benefit from that.