Iterates over the body a certain amount of times

@param {String} args The arguments to the command
@param {Function} define
@constructor
function ForCommand(args, define) {
    var lowerArgs = args.toLowerCase();
    var toIndex = lowerArgs.indexOf(' to ');
    if (toIndex === -1) throw new SyntaxError('FOR has no TO');
    var assignmentText = args.substring(0, toIndex).trim();

    var stepIndex = lowerArgs.indexOf(' step ');
    var upperLimitText, stepText;
    if (stepIndex === -1) {
        upperLimitText = args.substring(toIndex + 4).trim();
        stepText = '1';
    } else {
        upperLimitText = args.substring(toIndex + 4, stepIndex).trim();
        stepText = args.substring(stepIndex + 6).trim();
    }

    var assignmentEquals = assignmentText.indexOf('=');
    if (assignmentEquals === -1) throw new SyntaxError('Expected assignment');
    var variableName = assignmentText.substring(0, assignmentEquals).trim();
    var equalsExpression = assignmentText.substring(assignmentEquals + 1).trim();
    var assignmentExpr = new statements.AssignmentStatement(
            new statements.VariableStatement(variableName),
            new statements.ExpressionStatement(equalsExpression, define)
    );

    var upperLimitExpr = new statements.ExpressionStatement(upperLimitText, define);
    if (upperLimitExpr.error) throw upperLimitExpr.error;

    var stepExpr = new statements.ExpressionStatement(stepText, define);
    if (stepExpr.error) throw stepExpr.error;

    this.assignmentExpr = assignmentExpr;
    this.upperLimitExpr = upperLimitExpr;
    this.stepExpr = stepExpr;

    this.block = define({
        start: 'FOR',
        end: 'NEXT'
    });

    this.loopCount = 0;
}