3.1.5 Wrapping Up

The wrapped up simple expression evaluator code is:

union state_type {
    X1f4_E4_C_BILL bill;
    X1f4_E4_C_MODE mode;
    X1f4_E4_C_REAL real;
    X1f4_E4_C_TEXT text;
};

static int
select_function(const char *f, unsigned length, const void *context,
                const struct x1f4_function_type **function)
{
    int status = X1f4_E4_PARSE_ERROR;
    const struct x1f4_function_type *function_data;

    function_data = context;
    if (function_data) {
        while (function_data->name) {
            if (length == function_data->length
                && !memcmp((void *) f, function_data->name, length)) {
                break;
            }
            function_data++;
        }
        if (function_data->name) {
            status = 0;
            *function = function_data;
        }
    }

    return status;
}


static int
select_variable(const char *f, unsigned length, const void *context,
                const struct x1f4_variable_type **variable, void **state)
{
    return 1;
}


    ...

    struct x1f4_e4_type attributes;
    unsigned flags = 0;
    void *x1f4_expression;

    ...

    attributes.function_set.get = select_function;
    attributes.function_set.context = x1f4_e4_defaults;

    attributes.variable_set.get = select_variable;
    attributes.variable_set.context = NULL;

    attributes.terminator = 0;

    x1f4_llink_operator1s(&attributes.operator1s);
    x1f4_llink_operator2s(&attributes.operator2s);

    status = x1f4_init_expression
        (&x1f4_expression, expression, flags, &attributes);
    if (!status) {
        union state_type output;

        status = x1f4_link_expression(x1f4_expression, &output);
        if (!status) {
            unsigned type;

            type = x1f4_type_expression(x1f4_expression);
            if (type == X1f4_E4_BILL) {
                ... *(X1f4_E4_C_BILL *) &output ...
            } else {
	        if (type == X1f4_E4_MODE) {
	            ... *(X1f4_E4_C_MODE *) &output ...
	        } else {
	            if (type == X1f4_E4_REAL) {
	                ... *(X1f4_E4_C_REAL *) &output ...
	            } else {
	                if (type == X1f4_E4_TEXT) {
	                    ... *(X1f4_E4_C_TEXT *) &output ...
	                } else {
	                    no result, the expression evaluated void
	                }
	            }
	        }
            }
	}

        x1f4_fini_expression(&x1f4_expression);
    }

    ...

Note that this code was never tested as such. It may very well not work.