1. A computer-implemented method in a data processing hardware system including a processor, comprising: receiving a data processing instruction including an expression of a particular type; parsing the data processing instruction, using a template parser executing on the processor, by comparing the data processing instruction to a plurality of parsing templates; and determining, based upon the parsing, whether an evaluation template, from a plurality of evaluation templates, matches the data processing instruction based upon the particular type of the expression, wherein the evaluation template defines elements of a first type of expression used to control a conditional data processing operation, and the evaluation template is configured to generate optimized evaluation code for the expression of the first type.