Incidentally, the S combinator shows up in the J language as the "monadic hook". If f and g are functions, where f takes two arguments and is written infix (so

Incidentally, the S combinator shows up in the J language as the "monadic hook". If f and g are functions, where f takes two arguments and is written infix (so "x f y" is how you write the application of the arguments x and y to f), (f g) x equals x f (g x). It's useful for certain idioms, like "equals rounddown" (actually written =<.) to mean "is an integer". The thing with these combinators is that they are so low level, so names for them are almost useless. If you were to program with them directly, you'd learn to use and recognize useful sequences of them. At least that's the theory for APL-like languages like J.