A method, system and computer program product for modeling variables in subprograms of a HDL program. A subprogram is provided with an initial value of a variable of an element being modeled and the subprogram is stored in memory of a data processing system. In response to a subprogram call, a copy of the stored subprogram is provided to the requesting HDL program. During execution, the initial value of the variable in the provided copy of the subprogram may be modified by the HDL program, but the value retains unchanged in the stored subprogram.