A memoizer is a higher-order function that constructs memoizing functions.
visibly_memoize is a memoization combinator that exposes the memoization table. The function call visibly_memoize f returns a pair of a memoized function f' and a memoization table.
Cycle is raised by defensive_fix when a dependency cycle is detected.
defensive_fix works like fix, except it detects circular dependencies, which can arise if the second-order function supplied by the user does not follow a well-founded recursion pattern. When the user invokes f x, where f is the function returned by defensive_fix, if a cyclic dependency is detected, then Cycle (zs, z) is raised, where the list zs begins with z and continues with a series of intermediate keys, leading back to z. Note that undetected divergence remains possible; this corresponds to an infinite dependency chain, without a cycle.
val curried :
(((('a * 'b) -> 'c) -> ('a * 'b) -> 'c) -> ('a * 'b) -> 'c) ->
(('a -> 'b -> 'c) -> 'a -> 'b -> 'c) ->
'a ->
'b ->
'ccurried can be used to obtain a curried version of fix or defensive_fix in a concrete instance where the type key is a product type.