[Haskell-cafe] Metaprogramming in Haskell vs. Ocaml

Jacques Carette carette at mcmaster.ca
Mon Apr 5 19:50:27 EDT 2010

Casey McCann wrote:
> Not to speak for Jacques, 

and then you followed that up with a post with which I fully agree.


> but my impression is that while TH itself is
> typed--it's just more Haskell after all--it doesn't do much to prevent
> you from generating code that is not well-typed. Or even well-formed,
> for that matter; my initial attempts to learn how to use TH produced
> quite a few "that's impossible!" errors from GHC (I do not think that
> word means what it thinks it means).
> There's also type-level metaprogramming, as in e.g. HList, which is
> almost completely untyped. I have some personal library code that
> implements a simple meta-type system and it's a huge, horrid, painful
> mess for something with an expressive power no better than System F.
> In contrast, MetaOCaml seems to be some variety of a multi-stage
> system where metaprogramming blends smoothly into "regular"
> programming with a single, consistent type ensuring type safety at all
> points.
> - C.

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