text: /*
   *
   * Copyright 2015, Google Inc.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
   * met:
   *
   *     * Redistributions of source code must retain the above copyright
   * notice, this list of conditions and the following disclaimer.
   *     * Redistributions in binary form must reproduce the above
   * copyright notice, this list of conditions and the following disclaimer
   * in the documentation and/or other materials provided with the
   * distribution.
   *     * Neither the name of Google Inc. nor the names of its
   * contributors may be used to endorse or promote products derived from
   * this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   */
  
  #import <Foundation/Foundation.h>
  
  // A GRXWriteable is an object to which a sequence of values can be sent. The
  // sequence finishes with an optional error.
  @protocol GRXWriteable <NSObject>
  
  // Push the next value of the sequence to the receiving object.
  // TODO(jcanizales): Name it enumerator:(id<GRXEnumerator>) didProduceValue:(id)?
  - (void)didReceiveValue:(id)value;
  
  // Signal that the sequence is completed, or that an error ocurred. After this
  // message is sent to the instance, neither it nor didReceiveValue: may be
  // called again.
  // TODO(jcanizales): enumerator:(id<GRXEnumerator>) didFinishWithError:(NSError*)?
  - (void)didFinishWithError:(NSError *)errorOrNil;
  @end
  
  typedef void (^GRXValueHandler)(id value);
  typedef void (^GRXCompletionHandler)(NSError *errorOrNil);
  
  // Utility to create objects that conform to the GRXWriteable protocol, from
  // blocks that handle each of the two methods of the protocol.
  @interface GRXWriteable : NSObject<GRXWriteable>
  - (instancetype)initWithValueHandler:(GRXValueHandler)valueHandler
                     completionHandler:(GRXCompletionHandler)completionHandler
      NS_DESIGNATED_INITIALIZER;
  @end
  