The function of the Parse Service Routine is to syntax check command operands within the command buffer against the PCL, and build a PDL containing the results of the syntax check. In addition, the Parse Service Routine provides the following services that can be selected by the calling routine:

• It prompts the user if required operands are missing or incorrect.
• It issues messages for certain error conditions, or the validity checking routine or verify exit routine issues messages before requesting that parse terminate.
• It appends second-level messages, supplied by the calling program, to prompting messages.
• It passes control to a validity checking routine, supplied by the calling program, to do additional checking on a positional operand.
• It passes control to a verify exit routine, supplied by the calling program, to perform checking on a keyword operand that is not specifically defined in the PCL.
• It translates the command operands to uppercase.
• It substitutes default values for missing operands.
• It inserts implied keywords.