Laziest

Extends Enumerable#lazy (aka Enumerator::Lazy) with additional opportunities for lazy and especially partial evaluation. For example:

(1..Float::INFINITY).lazy.count > 10

evaluates almost instantaneously.

Add this line to your application's Gemfile:

gem 'laziest'

And then execute:

$ bundle

Or install it yourself as:

$ gem install laziest

Simply add this before working with any lazy enumerators:

require 'laziest'

This will extend Enumerator::Lazy (and the Enumerable#lazy method) to have lazier versions of the following methods:

• chunk
• count
• entries
• group_by
• max
• min
• minmax
• partition
• slice_before
• to_a

The somewhat ambitious goal is to defer as much as possible, while maintaining full compatibility with the existing API. Some more examples:

(1..Float::INFINITY).lazy.group_by{|x| x.to_s.length}[3].first(2)  # => [100, 101]
Prime.lazy.max > 1000  # => true
Prime.lazy.partition{|x| x%10 == 1}.all? {|x| x.count > 100} # => true

As with any self-respecting Ruby laziness, proxy classes (specifically, Promises from the promise ("promising future") gem) are abused, to ensure that traditional, non-lazy usage is correct.

(1..5).lazy.group_by(&:even?)  # => {false=>[1, 3, 5], true=>[2, 4]}

Not everything is as lazy as possible yet, but anything not lazy should still work, eventually, on anything finite.

Warning: Be careful in IRB! Remember that IRB calls #inspect on the result of any expression you type. This will almost always force a complete evaluation. For example, if you type this:

evens, odds = (1..Float::INFINITY).lazy.partition(&:even?)

This will attempt to #inspect the resulting arrays, and you have created an infinite loop. You can avoid this by adding a useless expression to the end:

evens, odds = (1..Float::INFINITY).lazy.partition(&:even?); nil
evens.first(10)

Of course, abusing one-liners is the easiest way to avoid this:

(1..Float::INFINITY).lazy.group_by(&:even?)[true].first(10)

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request