21. The non-transitory computer-readable storage medium of claim 17 , wherein the merge function performs a bit-by-bit merge of the first temporary result and the second temporary result.
17. A non-transitory computer-readable storage medium storing instructions that when executed by a computer causes the computer to interpret HDL (hardware description language) code, the instructions comprising: instructions for receiving the HDL code which describes an RTL (register transfer level) design, wherein the HDL code includes a conditional statement which executes a first branch or a second branch based on a value of a control expression; and instructions for interpreting the HDL code by: evaluating the control expression; and in response to determining that the value of the control expression is indeterminate, executing the first branch to obtain a first temporary result, executing the second branch to obtain a second temporary result, and determining a final result by merging the first temporary result and the second temporary result based on a merge function.