Simon Peyton-Jones wrote:
> > func n = map (func' n) [1..10]
> > func' x y = nfib x
>
> There isn't a free subexpression to lift out of func.
No, but as Adrian Hey quite correctly points out there is
a free subexpression in func' that can be lifted out of
its enclosing (\y->...).
> Try this
>
> func n = map nfib [1..10]
>
> Now the constant expression should be lifted out by GHC to give
>
> ans = map nfib [1..10]
> func n = ans
>
I have and it wasn't, the program I tried was as follows:
main = do
mapM print (map func ['a'..'z'])
return ()
func n = map nfib [1..10]
"map nfib [1..10]" was recomputed 26 times and not shared.
I have tried the same programs in a functional language
implementation which lets you choose either lazy or fully lazy
evaluation and I get all the results I expect.
Mike
