# `Expresso.Presenter.Verifier`
[🔗](https://github.com/rellen/expresso/blob/main/lib/expresso/presenter/verifier.ex#L1)

The Spark verifier of a presenter definition

It runs one time for each module that uses `Expresso.Presenter.Dsl`, when the
module compiles. It refuses these errors:

  * The option `state` does not hold exactly the fields of
    `Expresso.Presenter.Definition`, or a value has the wrong type.
  * The option `sync`, the option `reset` or the option `match` of a mode
    names an unknown field. The option `sync` or the option `reset` names
    `index`.
  * Two modes have the same name.
  * A command is not a command of `Expresso.Presenter.Definition`, or it gives
    a field a value of the wrong type.
  * A mode with the option `any` has bindings.
  * One event has two bindings in one mode. The list of keys would then show
    two functions for the event.
  * The event `:element` is in a mode without the option `element`.
  * A projection names an unknown field, or an attribute or a property with
    a wrong name. `Expresso.Presenter.Projection` describes the projections. An
    attribute with `flag: true` needs a field that is true or false, and a
    mark needs a field that holds a number.

The script in the browser reads the same fields and commands. Without the
verifier, the script finds such an error only when the presenter uses the
document.

# `verify`

```elixir
@spec verify(map()) :: :ok | {:error, Spark.Error.DslError.t()}
```

Make sure of the definition of a presenter

---

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