Maybe in ruby
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def Maybe(obj) | |
return Maybe.new(Nothing.new) if obj.nil? | |
return Maybe.new(obj) | |
end | |
class Nothing | |
def method_missing(*args, &block) | |
self | |
end | |
def ==(other) | |
other.is_a? Nothing | |
end | |
end | |
class Maybe | |
def initialize(value) | |
@value = value | |
end | |
def nothing? | |
@value.is_a? Nothing | |
end | |
alias :empty? :nothing? | |
def value(default) | |
return default if nothing? | |
return @value | |
end | |
def else(default) | |
return default if nothing? | |
return self | |
end | |
def method_missing(m, *args) | |
Maybe(@value.__send__(m, *args)) | |
end | |
def ==(other) | |
@value == other.instance_variable_get(:@value) | |
end | |
end |
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require 'minitest/autorun' | |
require_relative 'maybe' | |
class MaybeTest < MiniTest::Unit::TestCase | |
def test_nil | |
assert_equal Maybe(nil).a.b.c, Maybe(Nothing.new) | |
end | |
def test_some | |
assert_equal Maybe("Some").downcase, Maybe("some") | |
end | |
def test_value_with_nil | |
assert_equal Maybe(nil).a.value("foo"), "foo" | |
end | |
def test_value_with_some | |
assert_equal Maybe("Some").downcase.value("nothing"), "some" | |
end | |
def test_else_with_nil | |
assert_equal Maybe(nil).else("foo"), "foo" | |
end | |
def test_else_with_some | |
assert_equal Maybe("Foo").else("bar"), Maybe("Foo") | |
end | |
end |
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Please see https://github.com/pzol/monadic for a more complete implementation