It results into [1, 2, …(some xs satisfying cond)]. Emit does just that - emit another value into a context where for-expr was used. It emits some of x-es into

It results into [1, 2, …(some xs satisfying cond)]. Emit does just that - emit another value into a context where for-expr was used. It emits some of x-es into that array literal. filter cond xs More like 1:2:filter cond xs.