gistfile1.java

public abstract class Statement {
	
	public void execute(Map<String, Type> context);

	/**
	 * Updates the global context with the changes made in the local scope.
	 * Variables newly created in the scope are discarded.
	*/
	protected void updateContext(Map<String, Type> context, Map<String, Type> scopeContext) {
		for(String key : context.keySet()) {
			context.put(key, scopeContext.get(key));
		}
	}

	/**
	 * Executes the given statement in a local scope. 
	 * The variables in the context can be accessed and updates, but newly created variables will be discarded.
	*/
	protected void executeWithScope(Statement statement, Map<String, Type> context) {
		Map<String, Type> scopeContext = context.clone();
		statement.execute(scopeContext);
		updateContext(context, scopeContext);
	}

}


public class WhileStatement extends Statement{

	private Statement body;
	private Expression condition;

	public WhileStatement(Expression condition, Statement body){
		this.body = body;
		this.condition = condition;
	}

	@Override
	public void execute(){
		while (((BooleanType) condition.evaluate()).getValue()) {
			executeWithScope(body, context);
		}
	}

}