Arc Forum | x.y vs y.x

Arc Forum

1 point by binx 6119 days ago | 4 comments

I think it's better to write (x y) as y.x

For example, x.car means (car x) and x.len means (len x). And if you write a CLOS-style object system, with implicit currying, you can write (f obj x1 x2 ...) as (obj.f x1 x2 ...). By this, invoking generic functions are like passing messages in other languages.

In fact, I also like the idea that "." and "!" should be reserved for the user to extend arc.

5 points by vrk 6119 days ago | link

I disagree. x.y should remain (x y). It's plain confusing if you make it look like the dot notation in "object-oriented" languages, when it clearly is not. It's just an alternative way to write function application!

It would make more sense to provide the following kind of implicit currying:

  (def f (x y) ...)
  (let (x 'something)
    (= curried-f f.x))

  curried-f!else ; Calls (f 'something 'else)

Besides, if you switched the arguments or otherwise limited the usefulness of the new syntax to "(obj.f x1 x2)", you could never chain as in "f.obj.x1.x2"; instead, you would need to write "x2.x1.obj.f", which looks ridiculous.

I'm in favour of the dot syntax as infix function application operator. It reminds me of Edsger Dijkstra's reasoning (in fact, he also used the dot as function application). You may want to read [1] for the full story and other nice pondering about infix operators and syntax.

[1] http://www.cs.utexas.edu/~EWD/transcriptions/EWD13xx/EWD1300...

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3 points by binx 6119 days ago | link

Then what about "$"? Haskell uses "$" for infix function application operator. Composing objects and methods with "." or "->" is almost a de-facto standard that too many people have got used to...

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3 points by vrk 6119 days ago | link

The dot notation is used for at least two different purposes: accessing field values (C structures, for example) and calling methods on/sending messages to an object (Java, for example). Similarly the arrow notation is used for at least two different purposes: accessing field values through a pointer (pointers to C structures, for example) and calling methods on/sending messages to an object (Perl, for example).

Standard? I don't think so. They are used for very different purposes, and just because the convention of separating a record or an object and its attribute with a dot or an arrow is common is not reason enough to blindly adopt the same convention in a new programming language.

Does the dot notation as a record and field separator make sense? Maybe, if that's all you can do in your programming language. Take a look at Common Lisp defstruct for an example of another way to define structures and access fields.

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3 points by araujo 6119 days ago | link

This is not really a good idea. I think it'd get people to misunderstand what x.y really means , it could give the impression of some kind of method calling , with all the confusions this might bring along.

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