Since their introduction, copatterns have promised to extend functional languages—with their familiar pattern matching facilities—to synthesize and work with infinite objects through a finite set of observations. Thus far, their adoption in practice has been limited and primarily associated with specific tools like proof assistants. With that in mind, we aim to make copattern matching usable for ordinary functional programmers by implementing them as macros in the Scheme and Racket programming languages. Our approach focuses on composable copatterns, which can be combined in multiple directions and offer a new solution to the expression problem through novel forms of extensibility. To check the correctness of the implementation and to reason equationally about copattern-matching code, we describe an equational theory for copatterns with a sound, selective translation into \(\lambda \) -calculus.