--- jerzy.karczmarczuk@info.unicaen.fr wrote:
fix f = f (fix f) -- Here you have your Y. No typeless lambda.
g f n = n : f n -- This is a generic *non-recursive* `repeat` ones = fix g 1 -- Guess what.
Very nice! I honestly would not have expected this to work. Simple
cases of lazy evaluation are one thing, but this is impressive.
Incidentally, I only(!) have accces to Hugs here in the office, but
defining
fix f = f (fix f)
g f n = n : f n
h f = 1 : map (+1) f
I see that the number of reductions required for each successive term
in h actually seems to go down.
Main> take 1 (fix h)
[1]
(65 reductions, 95 cells)
Main> take 2 (fix h)
[1,2]
(96 reductions, 138 cells)
Main> take 3 (fix h)
[1,2,3]
(123 reductions, 178 cells)
Main> take 4 (fix h)
[1,2,3,4]
(150 reductions, 218 cells)
Main> take 5 (fix h)
[1,2,3,4,5]
(177 reductions, 258 cells)
Main> take 6 (fix h)
[1,2,3,4,5,6]
(204 reductions, 298 cells)
(In case it's not obvious, I'm a complete Haskell newbie, and find this
rather impressive.)
Main>
===
Gregory Woodhouse