The search order for functions is: internal routines take precedence, then built-in functions, and finally external functions.

Internal routines are not used if the function name is given as a literal string (that is, specified in quotation marks); in this case the function must be built-in or external. This lets you usurp the name of, say, a built-in function to extend its capabilities, yet still be able to call the built-in function when needed.

/* This internal DATE function modifies the          */
/* default for the DATE function to standard date.   */
date: procedure
      arg in
      if in='' then in='Standard'
      return 'DATE'(in)

Built-in functions have uppercase names, and so the name in the literal string must be in uppercase for the search to succeed, as in the example. The same is usually true of external functions. The search order for external functions and subroutines follows.

1. Check the following function packages defined for the language processor environment:
   • User function packages
   • Local function packages
   • System function packages
2. If a match to the function name is not found, the function search order flag (FUNCSOFL) is checked. The FUNCSOFL flag (see Flags and corresponding masks) indicates whether load libraries are searched before the search for a REXX exec.

   If the flag is off, check the load libraries. If a match to the function name is not found, search for a REXX program.

   If the flag is on, search for a REXX program. If a match to the function name is not found, check the load libraries.

   By default, the FUNCSOFL flag is off, which means that load libraries are searched before the search for a REXX exec.

   You can use TSO/E EXECUTIL RENAME to change functions in a function package directory. For more information, see EXECUTIL RENAME.

3. TSO/E uses the following order to search the load libraries:
   • Job pack area
   • ISPLLIB. If the user entered LIBDEF ISPLLIB ..., the system searches the new alternate library defined by LIBDEF followed by the ISPLLIB library.
   • Task library and all preceding task libraries
   • Step library. If there is no step library, the job library is searched, if one exists.
   • Link pack area (LPA)
   • Link library
4. The following list describes the steps used to search for a REXX exec for a function or subroutine call:

   Restriction: VLF is not searched for REXX execs called as functions or subroutines.

   1. Search the ddname from which the exec that is calling the function or subroutine was loaded. For example, if the calling exec was loaded from the DD MYAPPL, the system searches MYAPPL for the function or subroutine.
      Note: If the calling exec is running in a non-TSO/E address space and the exec (function or subroutine) being searched for was not found, the search for an exec ends. Note that depending on the setting of the FUNCSOFL flag, the load libraries may or may not have already been searched at this point.
   2. Search any exec libraries as defined by the TSO/E ALTLIB command
   3. Check the setting of the NOLOADDD flag (see Flags and corresponding masks).
      • If the NOLOADDD flag is off, search any data sets that are allocated to SYSEXEC. (SYSEXEC is the default system file in which you can store REXX execs; it is the default ddname specified in the LOADDD field in the module name table. See Module name table).

        If the function or subroutine is not found, search the data sets allocated to SYSPROC. If the function or subroutine is not found, the search for an exec ends. Note that depending on the setting of the FUNCSOFL flag, the load libraries may or may not have already been searched at this point.

      • If the NOLOADDD flag is on, search any data sets that are allocated to SYSPROC. If the function or subroutine is not found, the search for an exec ends. Note that depending on the setting of the FUNCSOFL flag, the load libraries may or may not have already been searched at this point.
      Note: With the defaults that TSO/E provides, the NOLOADDD flag is off. This means that SYSEXEC is searched before SYSPROC.

      You can control the NOLOADDD flag using the TSO/E REXX EXECUTIL command. For more information, see EXECUTIL.

Figure 1 illustrates how a call to an external function or subroutine is handled. After the user, local, and system function packages, and optionally, the load libraries are searched, if the function or subroutine was not found, the system searches for a REXX exec. The search for an exec is shown in part 2 of the figure.

Figure 1. External routine resolution and execution Part 1

Figure 2. External routine resolution and execution Part 2