Abstract: A method for conversion of digital computer source code software to operate in a system foreign to that from which the software originated. A library is created in which each entry incorporates the name of a code statement, or macro, which may require conversion and expanded code statements which may be selected to replace the macro. Each expanded code statement may be accompanied by one or more parametric triplets, each of which corresponds to a parameter within the expanded code and expresses a condition under which the expanded code is bypassed depending on the presence or absence of the parameter in any source code statement containing the macro. The source code statements are examined serially and any statement containing no macro entered in the library is passed to an output file, while any macro is replaced by any expanded code from the dictionary for which no bypass condition is satisfied.