  We describe a framework for multitask deep reinforcement learning guided by
policy sketches. Sketches annotate tasks with sequences of named subtasks,
providing information about high-level structural relationships among tasks but
not how to implement them---specifically not providing the detailed guidance
used by much previous work on learning policy abstractions for RL (e.g.
intermediate rewards, subtask completion signals, or intrinsic motivations). To
learn from sketches, we present a model that associates every subtask with a
modular subpolicy, and jointly maximizes reward over full task-specific
policies by tying parameters across shared subpolicies. Optimization is
accomplished via a decoupled actor--critic training objective that facilitates
learning common behaviors from multiple dissimilar reward functions. We
evaluate the effectiveness of our approach in three environments featuring both
discrete and continuous control, and with sparse rewards that can be obtained
only after completing a number of high-level subgoals. Experiments show that
using our approach to learn policies guided by sketches gives better
performance than existing techniques for learning task-specific or shared
policies, while naturally inducing a library of interpretable primitive
behaviors that can be recombined to rapidly adapt to new tasks.
