TAP is a better ?Hello World? ? Or The Challenge of Web-Application Development

We all know the infamous 'Hello World' applications to learn a programming language. But really - are you satisfied with a self-declaring one-liner to see how a language works? I’m certainly not. TAP - Twitter Application - is my approach to understand a language in more detail. TAP is a web application which produces HTML and CSS, talks with the Twitter API, and stores users and their tweets in a local database. Much to cover and thus much to learn how things work. This article explains the common functionality of TAP, and future posts cover implementation with Ruby, Python and more languages.

TAP Defined

Many of you already know or use the micro-blogging platform Twitter. User exchange small posts, called tweets in the Twitter jargon, either public visible or private. Tweets have a maximum length of 140 characters, thus requiring concessions to put something meaningful online. But hey, constraints are the fuel of creativity. Twitter also has a good documented API which allows to fetch posts from different users or the public timeline (recent posts of all users).

So what is TAP about? TAP allows to configure a set of users and store their tweets in a local database. You can see it as a personal Twitter hub. There is a dialogue to configure the registered users, you can view tweets with different filters, and a update TAP to fetch the newest tweets for all users. And this small application requires many stuff making traditional 'Hello World' apps child’s play. We need to filter URLs and invoke handlers, read and pass form & request parameters, render dynamic HTML, read & write to database and communicate with the Twitter API. That TAP's ground. Although the use cases are simple ones, combining all the little pieces is great for learning a languages capability and to get a feeling how things work.

See and read about the interface and upcoming posts athttp://blog.sebastianguenther.org/2010/05/24/tap-is-a-better-hello-world-or-the-challenge-of-web-application-development

Understanding Metaprogramming as Scope Manipulation

The common understanding of metaprogramming is to use a programming language for the manipulation of a realized program. In this article, I elaborate the scope concept as the internal representation of a programs structure. Metaprogramming is then explained as manipulating a programs scope.

Programs as Multi-Dimensional Scopes

A scope is the set of modules, classes, functions, constants and variables (generally called entities) which have a well defined visibility. For example, the global scope usually contains the core classes of the used language (like strings, integers, arrays) and other well known entities. A program either extends the global scope with its entities, or provides additional scopes. The entities of one scope are usually private, but can be made accessible from other scopes too. How new scopes are defined is dependent on and special to the used programming language: Scopes are created inside modules, classes, function declarations, or further expressions like control structures, iterations, or anonymous code blocks. The visibility of these scopes depends on the language: Typically, the methods and modules of classes are visible, but narrower scopes are not. In summary, a program consists of a set of scopes, each declaring their own set of entities.

Scopes are initially created by defining new entities. A declaration uses several expressions and statements to define a new scope - for example the definition of inner classes or methods. Declarations either happen intentionally as execution of manually written statements, or automatically by importing packages or modules from another scope, mix-in entities from modules, or copy entities with expressions from one scope to the current. After execution of the expressions, the scope will be populated with a number of entities, and is ready to be used in the program.

Read more at http://dsl-engineer.com/2010/05/14/understanding-metaprogramming-as-scope-manipulation-2.