The constructive approach to the formal definition of the semantics of programming languages has much in common with the notion that a language can be defined by an actual processor which compiles or interprets programs written in that language. The two approaches can be unified if the processor is written in a sufficiently powerful and expressive high-level language so that it closely models a formal definition for the processed language. The resulting processor has the conceptual clarity of the formal scheme as well as the advantages of being executable on a real computer. These points are illustrated by exhibiting a formal definition of a minilanguage using the Vienna Definition Language and an equivalent definition using ALGOL 68.