# `Statifier.Evaluator.Error`
[🔗](https://github.com/riddler/statifier-ex/blob/v2.0.0/lib/statifier/evaluator/error.ex#L1)

`Statifier.Evaluator.evaluate/2`'s own error value (ADR-0014 item 4).

`source` is the original expression string
(`Statifier.Machine.expr()`'s `{:compiled, _, source}` third element),
carried alongside `error` so a reporting site never has to thread the
source string separately just to render a message. `error` is predicator's
own error struct verbatim - `%Predicator.Errors.UndefinedVariableError{}`,
`%Predicator.Errors.TypeMismatchError{}`, `%Predicator.Errors.EvaluationError{}`,
or `%Predicator.Errors.ParseError{}` - never re-wrapped or reduced to a
message string, so a caller that wants to pattern-match the specific
failure still can.

`span` is lifted out of `error` for convenience (`Predicator.Errors.LocationError`
has no `:span` field, hence `Map.get/2` rather than `error.span`) and is
`nil` exactly when predicator itself could not attribute one - ADR-0014
item 4's own "nil when predicator cannot attribute one", not a sentinel
this module invents.

This struct carries no `owner` field: the raise site
(`Statifier.Interpreter.Content.raise_execution_error/4`) already stamps
`{:content, c_index, owner}` on the platform event, so the owner would be
a duplicate of information the caller already has, not something the
evaluator needs to originate.

# `t`

```elixir
@type t() :: %Statifier.Evaluator.Error{
  error: struct(),
  source: String.t(),
  span: term() | nil
}
```

# `new`

```elixir
@spec new(source :: String.t(), error :: struct()) :: t()
```

Builds an error value from the failing expression's `source` and
predicator's own `error` struct, lifting `error`'s `:span` field (when it
has one) up to the top level.

---

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