On Sat, Apr 19, 2008 at 07:37:50PM -0500, Creighton Hogg wrote:
This isn't about Haskell per se, but I was reading the old Meijer et al. paper "Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire" & I think there's a notational pun that's really confusing me. On page 12 we have the CataEval equation (|phi|) . in = phi . (|phi|)_L Now, the subscript L & the following example of cons lists implies that L is a functor in this equation, yet the line immediately after this equation says that "(CataEval) states how to evaluate an application of (|phi|) to an arbitrary element of L...." so then that makes it sound like the L here is the fixed point of some functor F, not the functor itself.
Yes, the explanatory text should say mu L instead of L.