5. Declarations

Variables must be declared before they are used. Aside from a few special cases, declarations have the following formats:

<qualifier> <type> <identifier> = <expression>;
<qualifier> <type> <identifier>;

Both declarations are creating a variable with an identifier of <identifier>, with type <type>, and optionally a type qualifier of <qualifier>.

The first declaration explicitly initializes the value of the new variable with the value of <expression>.

In Gazprea all variables must be initialized in a well defined manner in order to ensure functional purity. If the variables were not initialized to a known value their initial value might change depending on when the program is run. Therefore, the second declaration is equivalent to:

<qualifier> <type> <identifier> = null;

For simplicity Gazprea assumes that declarations can only appear at the beginning of a block. For instance this would not be legal in Gazprea:

integer i = 10;
if (blah) {
  i = i + 1;
  real i = 0;  // Illegal placement of a declaration.
}

because the declaration of the real version of i does not occur at the start of the block.

The following declaration placement is legal:

integer i = 10;
if (blah) {
  real i = 0;  // At the start of the block. All good.
  i = i + 1;
}

The declaration of a variable happens after initialization. Thus it is illegal to refer to a variable within its own initialization statement.

/* All of these declarations are illegal, they would result in garbage
   values. */
integer i = i;
integer v[10] = v[0] * 2;

An error message should be raised about the use of undeclared variables in these cases. If a variable of the same name is declared in an enclosing scope, then it is legal to use that in the initialization of a variable with the same name. For instance:

integer x = 7;
if (true) {
  integer y = x;  /* y gets a value of 7 */
  real x = x; /* Refers to the enclosing scope's 'x', so this is legal */

  /* Now 'x' refers to the real version, with a value of 7.0 */
}

5.1. Special cases

Special cases of declarations are covered in their respective sections.