So it sounds like a monoid is a: Function of arity-2 (possibly expressed as an infix operator) Which is closed over the set of values that are its arguments/p

So it sounds like a monoid is a: Function of arity-2 (possibly expressed as an infix operator) Which is closed over the set of values that are its arguments/parameters For a domain (set of input values) which contains a value that converts the function into an identity function when used. E.g. - Addition over real numbers (or integers...), becomes an identity function when one arg is 0 Multiplication over real numbers (or integers...), becomes an identity function when one arg is 1 Something along that line? I guess that makes it useful for a fold/reduce type function where the final result is the same type as the input stream, and the initial value can be identified as a known default.