Andrew Coppin wrote:
That seems simple enough (although problematic to implement). However, the Report seems to say that it matters whether or not the bindings are muturally recursive [but I'm not sure precisely *how* it matters...]
Seriously, check out the classic Milner paper. Of languages in the ML tradition, Haskell is actually a bit strange in that it doesn't require the programmer to explicitly annotate recursive functions and recursive groups. That's *very* nice for programmers (since the compiler needs to and can figure it out anyways), though it hides some of the implementation complexity since you need to discover the "implicit" annotations. Polymorphic recursion was one of the big bugbears in the original HM inference algorithm. We can deal with it now, like we can deal with rank-N polymorphism (aka polymorphic lambda-binding) and many other improvements, but it's easiest to start out with the original algorithm when learning everything. -- Live well, ~wren