unison-memo is a tiny Unison memoization library.
Install in Unison with the following ucm command:
pull https://github.com/anovstrup/unison-memo:.releases._v1 .external.anovstrup.memo.v1
Use the Memo.memo : '{e} a ->{e, Memo} a function to memoize a computation. For example, here is a memoized recursive implementation of the Fibonacci function:
memoFib : Nat ->{Memo} Nat
memoFib n =
Memo.memo 'let
if n < 2 then n
else memoFib (drop n 1) + memoFib (drop n 2))
A memoized computation must be evaluated in a context that provides the Memo ability. The Memo.run : '{e, Memo} a ->{e} a function provides one such evaluation context:
fib : Nat -> Nat
fib n = Memo.run '(memoFib n)
> fib 30
⧩
832040
Memo.run is backed by the Map data structure from the Unison base library, but alternative caching strategies can be used by implementing an alternative Memo handler. The Memo.run implementation ensures that the result of each (sub-)computation memoized with Memo.memo is evaluated only once (within an enclosing Memo.run thunk call). If such a (sub-)computation performs any effects using other abilities, those effects are also performed only once.