Dot
The ./2 (xfy, priority 800) operator that lets Prolog code chain member accesses fluently, e.g. Obj.foo(1).bar for "invoke foo(1) on Obj, then bar on the result".
'.'(Ref, Method) :- fluent_reduce([Ref | Method], _).As a clause in its own right, this lets a . expression also be used directly as a goal (e.g. X.println("hi") as a whole query), invoking the chain purely for its side effects and discarding the reduced result; capture the result instead with := (see ColonEquals).
This relies on ./2 being, by construction, the very same functor/arity Prolog uses for list cons cells: Obj.foo(1).bar parses (right-associatively) into .(Obj, .(foo(1), bar)), which is indistinguishable from the (improper) list [Obj, foo(1) | bar] -- so FluentReduce can walk it exactly like a list of "things to invoke in sequence" without any extra parsing.