[ruby-core:70264] [Ruby trunk - Feature #6284] Add composition for procs

Issue #6284 has been updated by Philippe Van Eerdenbrugghe.


Martin D端rst wrote:
> I'm teaching Haskell in a graduate class, so I'm quite familiar with function composition and use it a lot, but the original example isn't convincing at all. For me, in Ruby, something like val.strip.capitalize reads much, much better than some artificially forced function composition. If there were a method String#prepend, it would be even more natural: val.strip.capitalize.prepend('Title: ').
> 
> If there are better examples that feel more natural in Ruby, please post them here.

I fully agree with you that a good example really helps to understand the problem which lead to a better solution.

The few times I've missed function composition is ruby is always when I wanted to replace the same pattern : 

~~~
res = step1(base)
res = step2(res)
res = step3(res)
...
res
~~~
I hate having to mutate the res variable and I would hate even more creating different temp variables especially when I do not know how many steps there will be. I would like to be able to combine the steps then apply the step combination to *base*
There are a lot of examples for this pattern so here is one : data retrieval with ActiveRecord ( I assume most people know this library but this is only an example )

~~~
messages  = all_messages
messages = restrict_to_owner(messages, owner)
filters.each do |filter|
  messages = filter.apply(messages)
end
messages = messages.order(created_at: :asc)
messages = paginate(messages)
~~~

----------------------------------------
Feature #6284: Add composition for procs
https://bugs.ruby-lang.org/issues/6284#change-53689

* Author: Pablo Herrero
* Status: Feedback
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
=begin
It would be nice to be able to compose procs like functions in functional programming languages:

    to_camel = :capitalize.to_proc
    add_header = ->val {"Title: " + val}

    format_as_title = add_header << to_camel << :strip

instead of:

    format_as_title = lambda {|val| "Title: " + val.strip.capitalize }


It's pretty easy to implement in pure ruby:

  class Proc
    def << block
      proc { |*args| self.call( block.to_proc.call(*args) ) }
    end
  end
=end

---Files--------------------------------
0002-proc.c-Implement-Method-for-Method-composition.patch (2.71 KB)
0001-proc.c-Implement-Proc-for-Proc-composition.patch (3.73 KB)
0003-proc.c-Support-any-callable-when-composing-Procs.patch (4.01 KB)


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