@callback args() :: [arg()] | :var_args

The number and types of arguments supported.

@callback can_return_nil?(func :: map()) :: boolean()

Whether or not the function return nil.

@callback eager_evaluate?() :: boolean()

Whether or not the function can be evaluated eagerly. For example, now() cannot be.

@callback evaluate(func :: map()) :: :unknown | {:known, term()} | {:error, term()}

Evaluate a function when all arguments are known valid values

@callback evaluate_nil_inputs?() :: boolean()

If true, will be allowed to evaluate nil inputs.

If false (the default), any nil inputs will cause a nil return.

@callback name() :: atom()

The name of the function

@callback new([term()]) :: {:ok, term()} | {:error, String.t() | Exception.t()}

Instantiate a new function with the provided arguments

@callback partial_evaluate(func) :: {:ok, func} | {:error, term()} when func: map()

Evaluate a function when some or no arguments are known valid values

@callback predicate?() :: boolean()

Whether or not the function is a predicate (takes a reference as the first argument, a value as the second, and returns a boolean)

@callback private?() :: boolean()

Whether or not the function should be usable when parsing input.

@callback returns() ::
  [Ash.Type.t() | {Ash.Type.t(), constraints :: Keyword.t()}]
  | Ash.Type.t()
  | {Ash.Type.t(), constraints :: Keyword.t()}
  | :unknown

The return type for each corresponding set of args.