A lazy evaluation implementation:

lazy = SimplePromise.new { 1 + 1 } lazy + 3

1. 5

lazy = SimplePromise.new { puts “executing”; 1 + 1 } lazy + 3 (prints “executing”)

1. 5

A SimplePromise differs from the result of its promised block only in two ways.
First, #inspect shows that it is in fact a promise:

lazy = SimplePromise.new { 1 + 1 } lazy.inspect

1. #<SimplePromise computation=#<Proc:0×000@/foo.rb:44> result=[promised]>

lazy + 3 lazy.inspect

1. #<SimplePromise computation=#<Proc:0×000@/foo.rb:44> result=2>

Second, literal truthiness evaluations will always be positive:

lazy_true = SimplePromise.new { true } lazy_false = SimplePromise.new { false } lazy_true ? “positve truthiness” : “negative truthiness”

1. “positive truthiness”

lazy_false ? “positve truthiness” : “negative truthiness”

1. “positve truthiness”