Functional ruby

Functional RubyKerry Buckley, 10 November 2011

Lambda calculusLambda 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) ∈ ΛInstances of rule 2 are known as abstractions and instances of rule 3 areknown as applications.

Clear?

Clear?Me neither.

EnumerableThe Enumerable mixin provides collectionclasses with several traversal and searchingmethods, and with the ability to sort. Theclass must provide a method each, whichyields successive members of the collection.

Enumerableall? find minmax_byany? find_all none?chunk find_index one?collect first partitioncollect_concat flat_map reducecount grep rejectcycle group_by reverse_eachdetect include? selectdrop inject slice_beforedrop_while map sorteach_cons max sort_byeach_entry max_by takeeach_slice member? take_whileeach_with_index min to_aeach_with_object min_by zipentries minmax

EnumerableIf Enumerable#max, min, or sort is used,the objects in the collection must alsoimplement a meaningful <=> operator, asthese methods rely on an ordering betweenmembers of the collection.

Better iterationdef crappy_method results = [] @collection.each do |thing| results << thing.property end resultsenddef nicer_method @collection.map {|a| a.property }enddef more_concise_method @collection.map &:propertyend

each or map?collection.each do |a| do_something_with_side_effects(a)endanother_collection = collection.map {|a| transform(a) }

do…end or {…}?• do…end for multiple lines• {…} when chaining• do…end when there are side-effects• do…end for control ﬂow

Filteringdef crappy_filter matches = [] @collection.each do |item| matches << item if item.something? end matchesenddef nicer_sum @collection.select {|a| a.something? }enddef more_concise_sum @collection.select &:something?end

Proc objectspalindromic = proc {|s| s == s.reverse }words = File.read("/usr/share/dict/words").splitwords.select &palindromic #=> ["A", "a", "aa", "aba", ... "yoy", "Z", "z"]

injectdef crappy_sum sum = 0 @collection.each do |number| sum += number end sumenddef nicer_sum @collection.inject(0) {|a, n| a + n }enddef more_concise_sum @collection.inject &:+end

Chaining functionsdef crappy_sum_of_odd_numbers sum = 0 @collection.each do |number| sum += number if number.odd? end sumenddef sum_of_odd_numbers_using_inject @collection.inject(0) {|a, n| n.odd? ? a + n : a }enddef sum_of_odd_numbers_using_select_and_inject @collection.select(&:odd?).inject(&:+)end

Synonyms• collect = map• inject = reduce• collect_concat = flat_map• find = detect• find_all = select• to_a = entries• include? = member?

Functional ruby

by Kerry Buckley on Nov 10, 2011

Accessibility

Categories

Upload Details

Usage Rights

1 Embed 3

Statistics

Functional ruby Presentation Transcript