After a language is recognized, parsed, and transformed, for it's statements to carry force, there must be some means of realizing the semantics of the language. We will broadly label all means of attaching impetus to the statements of a language as Evaluation. In general, the evaluation of a language will perform some pre-defined process upon the language's input language.

One general class of evaluaton, which we shall label Interpretation, involves following the procedures laid out in the input document; while a second general class of evaluation, which we shall label Generation, is the production of one or more data artifacts. For instance the evaluation of dot files in the graphviz environment produces graphics files in various formats, and the produced files realize the semantics of their description files.

A more restricted subclass of the generative class of evaluation, which we shall label Language Production, produces artifacts which are expressions of the semantics of the input document in some language. Pretty-printers, which read a program, and write out the same program with ostensibly nicer formating, are evaluators which are language producing generators. Compilers are also language producing generators.

Our pattern language will focus on the patterns for Interpretation and patterns for Generation, though it may be possible to identify other general classes of evaluation.