# `Monty.Frameworks.Models.MotorPolicySelectors`
[🔗](https://github.com/d-led/ex.tbp.monty/blob/v0.1.0/packages/ex_tbp_monty_core/lib/monty/frameworks/models/motor_policy_selectors.ex#L1)

Choosing which policy drives the body on a given step.

Mirrors `tbp/monty/frameworks/models/motor_policy_selectors.py`, which holds
the selector interface and the two selectors Monty ships:

  * `...MotorPolicySelectors.MotorPolicySelector` — **ported**: the interface,
    `call/5` answering a `MotorPolicyResult` and the selector it updated;
  * `...MotorPolicySelectors.SinglePolicySelector` — **ported**: one policy,
    given the highest-confidence goal of the step;
  * `...MotorPolicySelectors.DistantPolicySelector` — **ported**: routes goals
    that name an object to a jump policy, goals from a sensor module to a
    look-at policy, and everything else to a default.

A policy here is a five-argument function — `(ctx, observations, state,
percept, goal)` — because that is the whole of what Monty's `__call__` is.
Holding the function rather than the class keeps a selector testable without a
policy, and lets a policy be any module's function that answers a
`MotorPolicyResult`.

# `from_config`

```elixir
@spec from_config(map()) ::
  Monty.Frameworks.Models.MotorPolicySelectors.MotorPolicySelector.t()
```

The selector a config describes.

    policy_selector:
      _target_: tbp.monty.frameworks.models.motor_policy_selectors.DistantPolicySelector
      jump_to_goal:
        _target_: ...JumpToGoal
      look_at_goal:
        _target_: ...LookAtGoal
      default:
        _target_: ...InformedPolicyRandomWalk

A selector's policies are configs themselves, so they are built the same way
it is — which is what makes the config the description of the body rather
than a list of names to look up.

# `highest_confidence_goal`

```elixir
@spec highest_confidence_goal([Monty.Cmp.Goal.t()]) :: Monty.Cmp.Goal.t()
```

The goal with the highest confidence, or the first of equal ones.

Monty sorts by confidence descending and takes the head, which for equal
confidences is the first: a stable sort is the whole of the tie-break. The
goals must not be empty — a step with no goals has nothing to choose between,
and the selectors ask that question before asking this one.

---

*Consult [api-reference.md](api-reference.md) for complete listing*