The Reader Monad lets you abstract away local state. You're on the right track with partial functions, but using a monad is cleaner (at least in Haskell...and

The Reader Monad lets you abstract away local state. You're on the right track with partial functions, but using a monad is cleaner (at least in Haskell...and I'd guess anywhere else). Essentially using the monad instead will let you remove all of the redundant function application you'd have to do otherwise. If you've managed to abstract this step away into a library, take a look at your abstraction. It's probably equivalent to Reader.