A Skill Block is the unit of reusable robot behaviour in Teach-and-Grow Learning. It carries a goal, a reusable strategy, the conditions under which it applies, the executors that can realize it, and a test of its effect. What is retained is the semantic effect; the physical realization — object bindings, grasp geometry, collision-free motion — is recomputed from the current scene each time the block runs.
A demonstration holds two different things at once: a strategy worth keeping, and physical details that belong to one scene. Consider placing a bowl on a plate. Across demonstrations the hand may approach from different directions along different paths. The stable part is the structure — acquire the requested bowl, establish that it is held, move toward the target relation, release it onto the plate. TGL separates that structure from the motion.
A block answers practical questions: what effect is intended, when does it apply, what evidence is needed, which executors can realize it, how is success observed, and what recovery is allowed? Verification has to refer to the intended physical effect. For an acquisition block, a closed gripper alone does not establish that the object is held; the test must check the effect the block claims.
A candidate is evaluated beyond its teaching demonstrations before it is admitted to the library. Its supported scope, executor compatibility, outcome test and recovery are checked. A weak candidate is narrowed or repaired. This makes library growth an explicit decision about a behaviour and the conditions under which it works, rather than a side effect of running more episodes.
At execution time the working plan is an ordered composition of blocks, and its remainder can change. A passed effect permits the next stage. A failed or inconclusive effect can prompt another observation, a different executor, or a revised route. This is the point where the AI Agent's reasoning meets physical feedback: what happens next depends on what actually happened.
No. A scripted motion fixes the trajectory. A Skill Block fixes the intended effect and the conditions, and delegates the motion to a compatible executor, so the same block can run in a different scene with different geometry.
A function call assumes its preconditions hold. A Skill Block states its supported conditions and an outcome test, and the execution loop checks the effect before allowing the next stage.
