I think the first time I saw a connection to polymorphic recursion was in Neil Mitchell's supero, which used it as a catch-all fallback plan. http://community.haskell.org/~ndm/downloads/slides-haskell_with_go_faster_st... -Edward On Thu, Jun 19, 2014 at 4:49 PM, Conal Elliott wrote:

Thanks, Ed. It hadn't occurred to me that defunctionalization might be useful for monomorphization. Do you know of a connection?

I'm using a perfect leaf tree type similar to the one you mentioned but indexed by depth:

...

data Tree :: (* -> *) -> Nat -> * -> * where L :: a -> Tree k 0 a B :: Tree k n (k a) -> Tree k (1+n) a

Similarly for "top-down" perfect leaf trees:

...

data Tree :: (* -> *) -> Nat -> * -> * where L :: a -> Tree k 0 a B :: k (Tree k n a) -> Tree k (1+n) a

This way, after monomorphization, there won't be any sums remaining.

-- Conal

On Thu, Jun 19, 2014 at 1:22 PM, Edward Kmett wrote:

...

Might you have more success with a Reynolds style defunctionalization pass for the polymorphic recursion you can't eliminate?

Then you wouldn't have to rule out things like

data Complete a = S (Complete (a,a)) | Z a

which don't pass that test.

-Edward

On Thu, Jun 19, 2014 at 3:28 PM, Conal Elliott wrote:

...

Has anyone worked on a monomorphizing transformation for GHC Core? I understand that polymorphic recursion presents a challenge, and I do indeed want to work with polymorphic recursion but only on types for which the recursion bottoms out statically (i.e., each recursive call is on a smaller type). I'm aiming at writing high-level polymorphic code and generating monomorphic code on unboxed values. This work is part of a project for compiling Haskell to hardware, described on my blog (http://conal.net).

Thanks, - Conal

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