lib/more/facets/continuation.rb in facets-2.7.0 vs lib/more/facets/continuation.rb in facets-2.8.0

@@ -1,57 +1,56 @@
-# = Continuation Extension
-#
-# Creates a continuation in a way that is easier to use than callcc.
-# On the initial call this will return the created Continuation and
-# the arguments you gave to Continuation.create in an Array. If you
-# then issue .call() on the Continuation execution will jump back to
-# the point of time where you initially invoked Continuation.create,
-# but this time it will return the Continuation and the arguments
-# you supplied in an Array.
-#
-# You can supply a block instead of default arguments which will
-# cause that block to be executed once and its result to be returned
-# along side the created Continuation, but this form is confusing
-# and does only rarely make sense.
-#
-#   # Count from 0 to 10
-#   cc, counter = Continuation.create(0)
-#   puts counter
-#   cc.call(counter + 1) if counter < 10
-#
-#   # Implement something similar to Array#inject using Continuations.
-#   # For simplicity's sake, this is not fully compatible with the real
-#   # inject. Make sure that you understand Array#inject before you try
-#   # to understand this.
-#   class Array
-#     def cc_inject(value = nil)
-#       copy = self.clone
-#       cc, result, item = Continuation.create(value, nil)
-#       next_item = copy.shift
-#       if result and item
-#         # Aggregate the result using the block.
-#         cc.call(yield(result, item), next_item)
-#       elsif next_item
-#         # item not yet set and Array is not empty:
-#         # This means we did not get a value and thus need to use the
-#         # first item from the Array before we can start using the
-#         # block to aggregate the result.
-#         cc.call(next_item, result)
-#       end
-#
-#       return result
-#    end
-#  end
-#  [1,2,3,4,5].cc_inject { |acc, n| acc + n } # => 15
-#
+if defined?(Continuation)
 
+  # = Continuation Extension
+  #
+  # Creates a continuation in a way that is easier to use than callcc.
+  # On the initial call this will return the created Continuation and
+  # the arguments you gave to Continuation.create in an Array. If you
+  # then issue .call() on the Continuation execution will jump back to
+  # the point of time where you initially invoked Continuation.create,
+  # but this time it will return the Continuation and the arguments
+  # you supplied in an Array.
+  #
+  # You can supply a block instead of default arguments which will
+  # cause that block to be executed once and its result to be returned
+  # along side the created Continuation, but this form is confusing
+  # and does only rarely make sense.
+  #
+  #   # Count from 0 to 10
+  #   cc, counter = Continuation.create(0)
+  #   puts counter
+  #   cc.call(counter + 1) if counter < 10
+  #
+  #   # Implement something similar to Array#inject using Continuations.
+  #   # For simplicity's sake, this is not fully compatible with the real
+  #   # inject. Make sure that you understand Array#inject before you try
+  #   # to understand this.
+  #   class Array
+  #     def cc_inject(value = nil)
+  #       copy = self.clone
+  #       cc, result, item = Continuation.create(value, nil)
+  #       next_item = copy.shift
+  #       if result and item
+  #         # Aggregate the result using the block.
+  #         cc.call(yield(result, item), next_item)
+  #       elsif next_item
+  #         # item not yet set and Array is not empty:
+  #         # This means we did not get a value and thus need to use the
+  #         # first item from the Array before we can start using the
+  #         # block to aggregate the result.
+  #         cc.call(next_item, result)
+  #       end
+  #
+  #       return result
+  #    end
+  #  end
+  #  [1,2,3,4,5].cc_inject { |acc, n| acc + n } # => 15
+  #
+  def Continuation.create(*args, &block)
+    args = [args] if not args.nil? and not args.is_a? Array # 1.6.8 compatibility
+    cc = nil; result = callcc {|c| cc = c; block.call(cc) if block and args.empty?}
+    result ||= args
+    return *[cc, *result]
+  end
 
-# There is no continuation in Ruby 1.9.
-
-raise "Ruby 1.9+ does not support continuations." unless Continuation
-
-def Continuation.create(*args, &block)
-  args = [args] if not args.nil? and not args.is_a? Array # 1.6.8 compatibility
-  cc = nil; result = callcc {|c| cc = c; block.call(cc) if block and args.empty?}
-  result ||= args
-  return *[cc, *result]
 end
+