[Haskell-cafe] Type system

[Don Stewart]

dpiponi:
> On Fri, Mar 14, 2008 at 11:50 AM, Andrew Coppin
> <andrewcoppin at btinternet.com> wrote:
> > Haskell has an expressive and powerful type system - which I love. It
> >  also has a seemingly endless list of weird and obscure type system
> >  extensions...And yet, none of this happens in any other programming language I've
> >  met.
> 
> Have you ever programmed in C++? Many of the exotic things that can be
> done in the Haskell type system can also be carried out in the C++
> type system - ranging from factoring integers at compile time to
> implementing highly optimised array and matrix DSLs. The difference
> between C++ and Haskell is that in C++ these techniques are highly ad
> hoc. In the Haskell world people are a lot more conservative and so
> only allow type system shenanigans if they are supported by some
> theory that allows us to reason nicely about them. As a side effect,
> each type system extension is relatively small and controlled. So when
> you see lots of Haskell type system extensions it looks like a big
> complicated system, but that's just an illusion that results from it
> being broken down into reasonable pieces. Read some of the source code
> for the Boost C++ template libraries (especially the template
> metaprogramming library) to see how complex the C++ type system really
> is.

As Manuel says, in C++ type level programming was an accident, in
Haskell, it was by design.