Most of the TSO/E REXX routines have parameter lists. The parameters provide information to the routine about what type of processing you want to perform and also provide a way for the routine to return information to the program that called it. All the parameter lists are passed to the routines in the same manner. Figure 1 shows the format of the parameter lists for the TSO/E REXX routines. A description of the parameter list follows the figure.

Figure 1. Overview of parameter lists for TSO/E REXX routines

Register 1 contains an address that points to a parameter list. The parameter list consists of a list of addresses. Each address in the parameter list points to a parameter. This is illustrated on the left side of the diagram in Figure 1. The end of the parameter list (the list of addresses) is indicated by the high-order bit of the last address being set to a binary 1.

The parameters themselves are shown on the right side of the diagram in Figure 1. The parameter value can be the data itself or it can be an address that points to the data.

All of the parameters for a specific routine might not be required. That is, some parameters may be optional. Because of this, the parameter lists are of variable length and the end of the parameter list must be indicated by the high-order bit being set on in the last address.

If there is an optional parameter you do not want to use and there are parameters after it you want to use, you can specify the address of the optional parameter in the parameter list, but set the optional parameter itself to either binary zeros (for numeric data or addresses) or to blanks (for character data). Otherwise, you can simply end the parameter list at the parameter before the optional parameter by setting the high-order bit on in the preceding parameter's address.

For example, suppose a routine has seven parameters and parameters 6 and 7 are optional. You do not want to use parameter 6, but you want to use parameter 7. In the parameter list, specify the address of parameter 6 and set the high-order bit on in the address of parameter 7. For parameter 6 itself, specify 0 or blanks, depending on whether the data is numeric or character data.

As another example, suppose the routine has seven parameters, parameters 6 and 7 are optional, and you do not want to use the optional parameters (parameters 6 and 7). You can end the parameter list at parameter 5 by setting the high-order bit of the address for parameter 5 on.

The individual descriptions of each routine in this book describe the parameters, the values you can specify for each parameter, and whether a parameter is optional.