Module Current_cache.S

module type WITH_DIGEST = sig ... end
module type WITH_MARSHAL = sig ... end
module type OPERATION = sig ... end
module type BUILDER = sig ... end

A builder generates an output value from an input key.

module type PUBLISHER = sig ... end

A publisher sets a key to a value.

module type GENERIC = sig ... end

The most general API. BUILDER and PUBLISHER are just special cases of this.