CONSTANT

The CONSTANT instruction defines a program constant.

Syntax

[PRIVATE|PUBLIC] CONSTANT constant-definition [,...]

where constant-definition is:

identifier [ data-type] = literal

identifier is the name of the constant to be defined.
data-type can be any built-in data type, except complex types like TEXT or BYTE.
literal must be an integer, decimal, string, or date/time literal, or an MDY() expression.
literal cannot be NULL.

Usage:

Constants define final static values that can be used in other instructions.

Constants can be defined with global, module, or function scope.

By default, module constants are private; They cannot be used by an other module of the program. To make a module constant public, add the PUBLIC keyword before CONSTANT. When a module constant is declared as public, it can be referenced by another module by using the IMPORT instruction.

When declaring a constant, the data type specification can be omitted. The literal value automatically defines the data type:

CONSTANT c1 = "Drink" -- Declares a STRING constant 
CONSTANT c2 = 4711    -- Declares an INTEGER constant

However, in some cases, you may need to specify the data type:

CONSTANT c1 SMALLINT = 12000 -- Would be an INTEGER by default

Constants can be used in variable, records, and array definitions:

CONSTANT n = 10
DEFINE a ARRAY[n] OF INTEGER

Constants can be used at any place in the language where you normally use literals:

CONSTANT n = 10
FOR i=1 TO n
  ...

Constants can be passed as function parameters, and returned from functions.

Define public constants in a module to be imported by others:

PUBLIC CONSTANT pi = 3.14159265

For date time constants, the value must be specified as an MDY(), DATETIME or INTERVAL literal:

CONSTANT my_date DATE = MDY(12,24,2011)
CONSTANT my_datetime DATETIME YEAR TO SECOND
              = DATETIME(2011-12-24 11:22:33) YEAR TO SECOND
CONSTANT my_interval INTERVAL HOUR(5) TO FRACTION(3)
              = INTERVAL(-54351:50:24.234) HOUR(5) TO FRACTION(3)

A constant cannot be used in the ORDER BY clause of a static SELECT statement, because the compiler considers identifiers after

ORDER
BY

as part of the SQL statement (i.e. column names), not as constants:

CONSTANT pos = 3
-- Next line will produce an error at runtime
SELECT * FROM customers ORDER BY pos

Automatic data type conversion can take place in some cases:

CONSTANT c1 CHAR(10) = "123"
CONSTANT c2 CHAR(10) = "abc"
DEFINE i INTEGER
FOR i = 1 TO c1 -- Constant "123" is converted to 123 integer
   ...
FOR i = 1 TO c2 -- Constant "abc" is converted to zero!
   ...

Character constants defined with a string literal that is longer than the length of the data type are truncated:

CONSTANT s CHAR(3) = "abcdef"
DISPLAY s  -- Displays "abc"

The compiler throws an error when an undefined symbol is used in a constant declaration:

CONSTANT s CHAR(c) = "abc"
-- Compiler error: c is not defined.

The compiler throws an error when a variable is used in a constant declaration:

DEFINE c INTEGER
CONSTANT s CHAR(c) = "abc"
-- Compiler error: c is a variable, not a constant.

The compiler throws an error when you try to assign a value to a constant:

CONSTANT c INTEGER = 123
LET c = 345
-- Runtime error: c is a constant.

The compiler throws an error when the symbol used is not defined as an integer constant:

CONSTANT c CHAR(10) = "123"
DEFINE s CHAR(c)
-- Compiler error: c is a not an integer constant.

You typically define common special characters with constants:

CONSTANT c_esc  = '\x1b'
CONSTANT c_tab  = '\t'
CONSTANT c_cr   = '\r'
CONSTANT c_lf   = '\n'
CONSTANT c_crlf = '\r\n'