I've made a bizarre little program that I don't understand the behaviour of. It's: data BoolList = End | Node Bool BoolList instance Show BoolList where show (Node False rest) = "F " ++ show rest show (Node True rest) = "T " ++ show rest show End = "<>" grow list = (Node False rest) where (Node _ rest) = add list add End = (Node True End) add (Node truth rest) = (Node truth (add rest)) The show is fine; it's the add that's confusing me. Where we have, grow list = (Node False rest) where (Node _ rest) = add list I don't really understand what's going on with this binding and matching using "where", so I'm not seeing how the True and False values are managing to propagate up to being results of grow as they do, e.g.:
grow End F <> grow (grow End) F T <>
I have Hudak, Peterson, Fasel's gentle introduction to Haskell 98, and Thompson's "Craft of Functional Programming" book - maybe I just missed something in them? Is it easy to explain what's going on with this "where" behaviour so that I could figure out what "grow"'s results are without evaluating examples? -- Mark