If a difference appears, I believe http://blog.johantibell.com/2010/09/static-argument-transformation.html would be involved. Also, the second map function could be inlined by GHC, avoiding calling "f" through a pointer because at the call site, we know what 'f' is (this is also mentionned in the blog post by Johan).

On Wed, Feb 13, 2013 at 9:55 AM, Andrew Polonsky <andrew.polonsky@gmail.com> wrote:

Hello,

Is there any difference in efficiency between these two functions, when compiled with all optimizations?

map f [] = []

map f (a:as) = f a : map f as

and

map f x = map' x where

   map' [] = []

   map' (a:as) = f a : map' as

Thanks,

Andrew

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Alp Mestanogullari