This interpreter is meant to be a reference implementation of the semantics of the embedded array language. The emphasis is on defining the semantics clearly, not on performance.

Surface types versus representation types

As a general rule, we perform all computations on representation types and we store all data as values of representation types. To guarantee the type safety of the interpreter, this currently implies a lot of conversions between surface and representation types. Optimising the code by eliminating back and forth conversions is fine, but only where it doesn't negatively affects clarity — after all, the main purpose of the interpreter is to serve as an executable specification.