Add `Enumerator.produce` from Ruby2.7

1 files changed, 36 insertions, 0 deletions

diff --git a/mrbgems/mruby-enumerator/mrblib/enumerator.rb b/mrbgems/mruby-enumerator/mrblib/enumerator.rb
index 89472ef01..d02caf5a0 100644
--- a/mrbgems/mruby-enumerator/mrblib/enumerator.rb
+++ b/mrbgems/mruby-enumerator/mrblib/enumerator.rb
@@ -556,6 +556,42 @@ class Enumerator
       self
     end
   end
+
+  ##
+  # call-seq:
+  #    Enumerator.produce(initial = nil) { |val| } -> enumerator
+  #
+  # Creates an infinite enumerator from any block, just called over and
+  # over.  Result of the previous iteration is passed to the next one.
+  # If +initial+ is provided, it is passed to the first iteration, and
+  # becomes the first element of the enumerator; if it is not provided,
+  # first iteration receives +nil+, and its result becomes first
+  # element of the iterator.
+  #
+  # Raising StopIteration from the block stops an iteration.
+  #
+  # Examples of usage:
+  #
+  #   Enumerator.produce(1, &:succ)   # => enumerator of 1, 2, 3, 4, ....
+  #
+  #   Enumerator.produce { rand(10) } # => infinite random number sequence
+  #
+  #   ancestors = Enumerator.produce(node) { |prev| node = prev.parent or raise StopIteration }
+  #   enclosing_section = ancestors.find { |n| n.type == :section }
+  def Enumerator.produce(init=NONE, &block)
+    raise ArgumentError, "no block given" if block.nil?
+    Enumerator.new do |y|
+      if init == NONE
+        val = nil
+      else
+        val = init
+        y.yield(val)
+      end
+      loop do
+        y.yield(val = block.call(val))
+      end
+    end
+  end
 end
 
 module Kernel