Edit: iPhone posted to root, meant in reply to top voted comment sry! don't think that's the underlying point at all. A functional Language gives the compiler

Edit: iPhone posted to root, meant in reply to top voted comment sry! don't think that's the underlying point at all. A functional Language gives the compiler more room to optimize - the compiler has more information because a functional language let's the programmer express constraints in ways imperative languages can't - the compiler fundamentally knows more and thus can generate better machine code. The productivity benefits of HLLs are secondary to this discussion.