A function in DM has a name, an argument list, a return type, and a body. In C++ and thus in DM, all functions must be declared before they are used. For instance, "result (EMadd (1,2) + "\n")" in Figure 1121 cannot be the first line in the script because this use has to locate after the function EMadd is declared, namely the block for "number EMadd( number EMa, number EMb ) ...".

Figure 1121. Function and argument list. (Script)

In C++ and DM, you can give a parameter a default value that is automatically used when no argument corresponding to that parameter is specified in a call to a function. Default arguments can be used to simplify calls to complex functions. On the other hand, such arguments can sometimes be used as a "shortcut" form of function overloading. A default argument is specified in a manner, syntactically, similar to a variable initialization.

One reason that default arguments are used is that they enable the programmer to manage greater complexity. In such situations, quite frequently a function will contain more parameters than are required for its most common usage. Therefore, when the default arguments apply, you only need remember and specify the arguments that are meaningful to the exact situation, not all those needed for the most general cases. Some important points to remember, when you create a function that has default argument values, are:
        i) The default values must be specified only once. However, you can still specify different default arguments for each version of an overloaded function.
        ii) This specification must happen the first time the function is declared within the file.
        iii) You cannot specify a non-defaulting parameter once you’ve begun defining parameters that take default values.