[ANN] Iterators

On 23 August 2019 at 16.15.31, Julien ([hidden email]) wrote:

Hello,

I wanted to have an iterator framework for Pharo for a long time.

So I started building it step by step and today I think that, while it still requires more documentation, it is ready to be announced and used by others.

I present you Iterators : https://github.com/juliendelplanque/Iterators

The idea is that, as described by the iterator design pattern, any object that needs to be walked provides one or many iterators.

In the library, #iterator method is the convention to get the default iterator of any object (if it has one).

Iterators provides a DSL to deal with iterators combination.

It is inspired from shell’s streams manipulation syntax:

- The pipe "|" allows one to chain iterators

- The ">" allows one to create a new collection with data transformed through chained iterators

- The ">>" allows one to fill an existing collection with data transformed through chained iterators

 

For example, one can write:

iterator := #(1 2 3) iterator.

iterator

| [ :x | x * 2 ] collectIt

| [ :x :y | x + y ] reduceIt

> Array "#(12)"

Or

iterator := #(1 2 3) iterator.

collectionToFill := OrderedCollection new.

iterator

| [ :x | x * 2 ] collectIt

| [ :x :y | x + y ] reduceIt

> collectionToFill.

collectionToFill "anOrderedCollection(12)"

The equivalent of "/dev/null" in Linux also exists:

iterator := #(1 2 3) iterator.

iterator

| [ :x | x * 2 ] collectIt

| [ :object | object logCr ] doIt "Just print incoming objects in transcript."

> NullAddableObject "Special object that ignore incoming objects."

There are documentation and examples on the GitHub repository.

—

Initially, the goal was to avoid to duplicate all collection’s iterator methods (e.g. #collect:, #select:, etc) in composite objects.

Thus, it provides an IteratorWithCollectionAPI which wrap an iterator and provides all the methods we want (#collect:, #select:, …).

Via IteratorWithCollectionAPI, your objects automatically gets the Collection API, you just need to access it via #iterator message:

myObject iterator select: [ :x | x isFoo ]

This is another way to use the framework, just to avoid code duplication.

—

Future work is to provide the possibility to have iterator with multiple inputs.

I already have an undocumented prototype on the repository that works like this:

it1 := (1 to: 10) iterator.

it2 := (1 to: 10) iterator.

it1 & it2

| [ :x :y | x@y ] mergeIt

> Array. "{(1@1). (2@2). (3@3). (4@4). (5@5). (6@6). (7@7). (8@8). (9@9). (10@10)}"

Yes, "&" operator will again kind of mimic the one from the shell.

—

Hope it helps other people.

Feedback is welcome.

Cheers,

Julien

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Julien Delplanque
Doctorant à l’Université de Lille

http://juliendelplanque.be/phd.html
Equipe Rmod, Inria

Bâtiment B 40, Avenue Halley 59650 Villeneuve d'Ascq

Numéro de téléphone: +333 59 35 86 40