On Fri, Mar 14, 2008 at 11:50 AM, Andrew Coppin
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. -- Dan