OftLisp is a strict language, with side effects.
Nonetheless, most effects are not explicitly present.
The main examples are errors, (mutable) state, and nondeterminism.
The traditional (in Haskell, at least) approach to modelling these effects (possibly in composition) is that of monads and monad transformer stacks.
However, in a dynamically typed setting, monad transformer stacks are awkward to use -- since one doesn't have types to help dispatch the lift function, one must have, for example, a lift-error-through-state-to-nondet function.
There are alternate approaches, including Kleisli Functors and Algebraic Effects.
Monads
Benefits:
- Familiar
do-notation
Disadvantages:
- Harder to explain than "composition of functions with effects"
- (Actually, could probably teach with Kleisli composition first, then monad bind)
Algebraic Effects
Benefits:
- Cleaner than a monad transformer stack
- Looks actually possible to implement in a dynamic setting...
Mixed?
- Compiles to CPS
Disadvantages:
- Requires a base monad
Kleisli Functors
Benefits:
- Can abstract inner effect representation completely
- Instead of
(a -> State b), can write(StateKA a b)
- Instead of
- Simpler laws, rewrite process is fairly intuitive
- Models a category more-or-less explicitly
Disadvantages:
kmapstill needs to be created for transformer stacksdo-notation becomes a lot more complex