@head
@title Defining global variables and constants

<p>C modules may define global variables and constants. There are two different
kinds of constants (symbolic and empty) that are useful in different contexts.
The initialization of the value of an empty constant must happen in the
Main function of the module, as described below.

@h2 Defining global variables

@fun A_VAR(name)
@desc Define a global variable with the specified name in the module. Its value
      will be initialized to nil.
      @see You may use the API functions
         @ref{AGetGlobalNum}, @ref{ASetGlobalByNum}, @ref{AGlobal} and
        @ref{AGlobalByNum} to set and query the value of the variable.
      @end
@end

@h2 Defining constants

@fun A_EMPTY_CONST(name)
@desc Define a global constant with the specified name in the module. Its value
      will be initialized to nil. A constant with a nil value is mostly
      useless, so you can set the value of the constant using the two API
      functions @ref{ASetConstGlobalByNum} and @ref{AGetGlobalNum}.
      @note You must set the value of a constant only once in the Main function
            of the module that defined the constant.
      @end

      <p>Here is an example of defining a constant named Three with value 3:

      @example
        static AValue Main(AThread *t, AValue *frame)
        {
            int threeNum = AGetGlobalNum(t, "example::Three");
            frame[0] = AMakeInt(t, 3);
            ASetConstGlobalByNum(t, threeNum, frame[0]);
            return ANil;
        }

        A_MODULE(example, "example")
            A_EMPTY_CONST("Three")
            A_DEF("Main", 0, 1, Main)
        A_END_MODULE()
      @end
@end

@fun A_SYMBOLIC_CONST(name)
@desc Define a symbolic constant with the specified name in the module. Its
      value will be initialized to a @ref{std::Constant} value, similar to
      using a global uninitialized const definition in Alore code. You must
      not try to change the value of a symbolic constant using
      @ref{ASetGlobalByNum} or other means.
@end