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What is the Ruby equivalent of Haskell's scanl?

This question presents a version of Haskell's scanl in Python, but is there a Ruby version of this function?

Solution

  • Probably a nicer version could be written, but this is what I came up with:

    require 'spec_helper'

class Array
  def scanl accumulator, &block
    results = [accumulator] + self
    results.each_with_index do |e, i|
      results[i] = block.call(accumulator, e)
      accumulator = results[i]
    end
    results
  end
end

describe "#scanl" do
  it 'is similar to foldl, but returns a list of successive reduced values from the left' do
    # example from http://learnyouahaskell.com/higher-order-functions
    expect([3, 5, 2, 1].scanl(0, &:+)).to eq([0,3,8,10,11])
  end
end

    I considered changing scanl to take just a method name like :+ instead of a block to be more like reduce. Thoughts?