Reinventing the wheel: the fluent interface design pattern | Hacker News Reader

Reinventing the wheel: the fluent interface design pattern

lexandera.com

4 pointsnimbix6 comments

That's totally wrong. The point of this style of programming is allow a series of function calls to be written as a linear chain of expressions. It comes from Smalltalk via Eric Evans, who popularized it in the Java world (http://www.martinfowler.com/bliki/FluentInterface.html). This style is favored by people who agree that side effects should be avoided but who don't like to build functional expressions with many levels of nesting (à la Lisp). Evans compared these composite linear expressions to noun phrases in English and argued that they can be a more natural way to express domain concepts in code.

The "with" control structure only resembles this in the degenerate case where every expression in the chain evaluates to the exact same object. Not only that, the "with" keyword expects a series of statements (as opposed to expressions), and that is the exact opposite of what the chaining style is about. This is easily seen in the author's own example: each member of the sequence has to end in a semicolon (i.e. is a statement rather than an expression), so you don't have a single composite expression at all, only a slightly more compact procedural script.

You're right, it definitely comes from Smalltalk. For those who aren't familar with Smalltalk, you can use the ';' operator to send a sequence of messages to the same object. The example in the article would look something like this:

  mainFrame := JFrame new: 'Hello World';  
      add: label withAlignment: BorderLayout.CENTER;  
      addWindowListener: MainFrameListener new;  
      setDefaultCloseOperation: JFrame.DO_NOTHING_ON_CLOSE;  
      pack;  
      setLocationRelativeTo: nil;  
      setVisible: True;
      yourself.

(The result of a chained method expression is the result of the last method call, thus the 'yourself' message at the end so that the object itself is stored into mainFrame.)

Sigh...I miss Smalltalk.

"Yes, you’re right! It looks remarkably like the “with” control structure available in Delphi/Pascal and VisualBasic!"

Those who do not understand Lisp are doomed to reinvent it, poorly. :-)

Fairly good intro article though.

As one dedicated Lisper to another, I think you're missing the point here. S-expressions are inherently nested, and the chaining style is about avoiding that (while still being side-effect free). I wrote about this a long time ago on HN... let me see if I can dig up the link.

Edit: here's one, though I remember writing something else with examples. Oh well. http://news.ycombinator.com/item?id=304871

Good point. One way to do it might be to reify the object instance pointer to a first-class argument (usually the first.) Another way is with a dynamic variable self (might be preferable, since you don't have to break function signatures.)

Yet another option might be with a custom method combination, which is overkill :-P

Any other ideas? or am I too off the ball park?

Well, the conclusion I came to was that trying to make Lisp less nested would be like trying to make the North Pole less arctic. If you don't like programming that way, you probably aren't using Lisp in the first place. There are a few exceptions, of course (I like loop quite a bit).

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