Restricted expressions

Where PL/I requires a (possibly signed) constant, a restricted expression can be used.

A restricted expression is an expression whose value is calculated at compile time and used as a constant. For example, you can use expressions to define constants required for the following:

Extents in static, parameter, and based declarations
Extents in entry descriptions
Values and iteration factors to be used in static initialization

A restricted expression is identical to a normal expression but requires that each operand be one of the following:

A constant or a named constant
A named constant must be declared before it is used. A reference to an element of a one-dimensional STATIC NONASGN array with the INITIAL attribute will also be treated as a named constant if the subscript is a FIXED DEC(p,0) value with p <= 3 and if the array elements are numeric.
A built-in function that is applied to a restricted expression or restricted expressions, where the built-in function is from the following categories:
- String-handling
- Arithmetic (except RANDOM)
- Mathematical (if all arguments are REAL)
- Floating-point inquiry
- Floating-point manipulation
- Integer manipulation
- Precision-handling
- Array-handling functions: DIMACROSS, DIMENSION, HBOUND, HBOUNDACROSS, LBOUND, and LBOUNDACROSS
- Storage-control functions: BINARYVALUE, LENGTH, NULL, OFFSETVALUE, POINTERVALUE, SIZE, STORAGE, and SYSNULL
- Miscellaneous functions: BYTE, CHARVAL, COLLATE, INDICATORS, PACKAGENAME, POPCNT, PROCEDURENAME, RANK, SOURCEFILE, SOURCELINE, and WCHARVAL
Type functions: BIND, CAST, FIRST, LAST, RESPEC, SIZE, and VALUE

Examples

  dcl Max_names fixed bin value (1000),
      Name_size fixed bin value (30),
      Addr_size fixed bin value (20),
      Addr_lines fixed bin value (4);
  dcl 1 Name_addr(Max_names),
        2 Name char(Name_size),
        2 * union,
          3 Address char(Addr_lines*Addr_size), /* address    */
          3 addr(Addr_lines) char(Addr_size),
        2 * char(0);
  dcl One_Name_addr char(size(Name_addr(1)));   /* 1 name/addr*/
  dcl Two_Name_addr char(length(One_Name_addr)
                         *2);                /* 2 name/addrs  */
  dcl Name_or_addr char(max(Name_size,Addr_size)) based;

  dcl Ar(10) pointer;
  dcl Ex     entry( dim(lbound(Ar):hbound(Ar)) pointer);
  dcl Identical_to_Ar( lbound(Ar):hbound(Ar) ) pointer;

If you change the value of any of the named constants in the example, all of the dependent declarations are automatically reevaluated.

Published: 23 December 2018