Extend.h  -- Extend System header file
------------------------------------------------------------------------------
 _parc()     Retrieve a character parameter
 _parclen()  Retrieve the length of a character parameter
 _pards()    Retrieve a date parameter as a string
 _parinfa()  Determine the length or element type of an array parameter
 _parinfo()  Determine the parameter count or the data type of a parameter
 _parl()     Retrieve a logical parameter as an int
 _parnd()    Retrieve a numeric parameter as a double
 _parni()    Retrieve a numeric parameter as an int
 _parnl()    Retrieve a numeric parameter as a long
 _ret()      Post a NIL return value
 _retc()     Post a character return value using a null terminated string
 _retclen()  Post a character return value with explicit length              .
 _retds()    Post a date return value using a date string
 _retl()     Post a logical return value
 _retnd()    Post a numeric return value using a double
 _retni()    Post a numeric return value using an int
 _retnl()    Post a numeric return value using a long
 _storc()    Assign a null terminated string to a referenced variable
 _storclen() Assign a string of explicit length to a referenced variable     .
 _stords()   Assign a date string to a referenced variable
 _storl()    Assign a logical value to a referenced variable
 _stornd()   Assign a numeric value to a referenced variable using a double
 _storni()   Assign a numeric value to a referenced variable using an int
 _stornl()   Assign a numeric value to a referenced variable using a long
 _xalloc()   Allocate memory and return NULL if unsuccessful
 _xfree()    Free allocated memory
 _xgrab()    Allocate memory, generating an error if unsuccessful
 _xunlock()  Unlock all VM segments locked by _parc()                        .