Functional ruby
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The document explains lambda calculus and the enumerable mixin in Ruby, detailing the structure of lambda expressions and how to traverse and search collections. It provides various methods for iteration and filtering in Ruby, along with examples illustrating different levels of code conciseness. Additionally, it lists synonyms for certain enumerable methods to enhance understanding of their usage.
![Better iteration
def crappy_method
results = []
@collection.each do |thing|
results << thing.property
end
results
end
def nicer_method
@collection.map {|a| a.property }
end
def more_concise_method
@collection.map &:property
end](https://image.slidesharecdn.com/functionalruby-111110085424-phpapp02/85/Functional-ruby-9-320.jpg)
![Filtering
def crappy_filter
matches = []
@collection.each do |item|
matches << item if item.something?
end
matches
end
def nicer_sum
@collection.select {|a| a.something? }
end
def more_concise_sum
@collection.select &:something?
end](https://image.slidesharecdn.com/functionalruby-111110085424-phpapp02/85/Functional-ruby-12-320.jpg)
![Proc objects
palindromic = proc {|s| s == s.reverse }
words = File.read("/usr/share/dict/words").split
words.select &palindromic
#=> ["A", "a", "aa", "aba", ... "yoy", "Z", "z"]](https://image.slidesharecdn.com/functionalruby-111110085424-phpapp02/85/Functional-ruby-13-320.jpg)
Functional ruby
- 1. Functional Ruby Kerry Buckley, 10 November 2011
- 2. λ
- 3. Lambda calculus Lambda expressions are composed of variables v1, v2, ..., vn, ... the abstraction symbols λ and . parentheses ( ) The set of lambda expressions, Λ, can be defined recursively: 1. If x is a variable, then x ∈ Λ 2. If x is a variable and M ∈ Λ, then (λx.M) ∈ Λ 3. If M, N ∈ Λ, then (M N) ∈ Λ Instances of rule 2 are known as abstractions and instances of rule 3 are known as applications.
- 4. Clear?
- 6. Enumerable The Enumerable mixin provides collection classes with several traversal and searching methods, and with the ability to sort. The class must provide a method each, which yields successive members of the collection.
- 7. Enumerable all? find minmax_by any? find_all none? chunk find_index one? collect first partition collect_concat flat_map reduce count grep reject cycle group_by reverse_each detect include? select drop inject slice_before drop_while map sort each_cons max sort_by each_entry max_by take each_slice member? take_while each_with_index min to_a each_with_object min_by zip entries minmax
- 8. Enumerable If Enumerable#max, min, or sort is used, the objects in the collection must also implement a meaningful <=> operator, as these methods rely on an ordering between members of the collection.
- 9. Better iteration def crappy_method results = [] @collection.each do |thing| results << thing.property end results end def nicer_method @collection.map {|a| a.property } end def more_concise_method @collection.map &:property end
- 10. each or map? collection.each do |a| do_something_with_side_effects(a) end another_collection = collection.map {|a| transform(a) }
- 11. do…end or {…}? • do…end for multiple lines • {…} when chaining • do…end when there are side-effects • do…end for control flow
- 12. Filtering def crappy_filter matches = [] @collection.each do |item| matches << item if item.something? end matches end def nicer_sum @collection.select {|a| a.something? } end def more_concise_sum @collection.select &:something? end
- 13. Proc objects palindromic = proc {|s| s == s.reverse } words = File.read("/usr/share/dict/words").split words.select &palindromic #=> ["A", "a", "aa", "aba", ... "yoy", "Z", "z"]
- 14. inject def crappy_sum sum = 0 @collection.each do |number| sum += number end sum end def nicer_sum @collection.inject(0) {|a, n| a + n } end def more_concise_sum @collection.inject &:+ end
- 15. Chaining functions def crappy_sum_of_odd_numbers sum = 0 @collection.each do |number| sum += number if number.odd? end sum end def sum_of_odd_numbers_using_inject @collection.inject(0) {|a, n| n.odd? ? a + n : a } end def sum_of_odd_numbers_using_select_and_inject @collection.select(&:odd?).inject(&:+) end
- 16. Synonyms • collect = map • inject = reduce • collect_concat = flat_map • find = detect • find_all = select • to_a = entries • include? = member?