1. A method of generating a parameter value for an executable statement, comprising: in a plurality of program statements, identifying by a data processing system, an input statement, wherein the input statement comprises input information; in the plurality of program statements, identifying by the data processing system, an output statement associated with the input statement; wherein: the output statement comprises a reference to a temporary data set, and another of the plurality of program statements also includes a parameter reference to the temporary data set; modifying, by the data processing system, the input information to produce modified input information, wherein the modifying comprises performing symbolic substitution on at least a portion of the input information; and outputting according to the output statement, by the data processing system, the modified input information to the temporary data set.