ezyang’s blog

the arc of software bends towards understanding

Type manipulation: Tricks of the trade

I present here a few pieces of folklore, well known to those practiced in Haskell, that I've found to be really useful techniques when analyzing code whose types don't seem to make any sense. We'll build practical techniques for reasoning about types, to be able to derive the type of fmap fmap fmap by ourselves. […]

  • February 19, 2010