# `Feel.Runtime.Kind`
[🔗](https://github.com/FeeJai/BDM/blob/feel-v0.1.0/apps/feel/lib/feel/runtime/kind.ex#L1)

The kind of a value: which row of the semantic tables of DMN 1.6 (section
10.3.2.15) applies to it.

The tables speak of "kinds" and "datatypes": two operands must be of the same
kind for `=` and `<`, and `+` is defined for some pairs of kinds only. The kind of
a value is one of the atoms that `Feel.Type` uses for the primitive types, or
`:list`, `:context`, `:range`, `:function`, or `:null`. A term that is not a FEEL
value at all, such as a float or an atom, has the kind `:unknown`, so a host that
binds one gets a type mismatch and not a crash.

A kind is looked up from the outermost shape of the value alone: the elements of
a list are not examined.

# `t`

```elixir
@type t() ::
  :null
  | :boolean
  | :string
  | :number
  | :date
  | :time
  | :date_and_time
  | :years_and_months_duration
  | :days_and_time_duration
  | :range
  | :list
  | :context
  | :function
  | :unknown
```

# `name`

```elixir
@spec name(t()) :: String.t()
```

Returns the name of a kind as FEEL writes it, for messages.

    iex> Feel.Runtime.Kind.name(:date_and_time)
    "date and time"
    iex> Feel.Runtime.Kind.name(:null)
    "null"

# `of`

```elixir
@spec of(term()) :: t()
```

Returns the kind of a value.

    iex> Feel.Runtime.Kind.of(Decimal.new(1))
    :number
    iex> Feel.Runtime.Kind.of(nil)
    :null
    iex> Feel.Runtime.Kind.of(%{"a" => 1})
    :context
    iex> Feel.Runtime.Kind.of(1.5)
    :unknown

# `string?`

```elixir
@spec string?(term()) :: boolean()
```

Returns `true` for a string of FEEL: a binary that is valid UTF-8 (`Feel.Value.String.value?/1`).

`of/1` calls any binary a string, since the operators take it as one, and a value that is bound to a name declared as a
`string` has to be a valid one (`Feel.Runtime.BindingTypes`, D-138): this is that test, for the code that checks it itself
(the BEAM backend's fast path, D-164).

    iex> Feel.Runtime.Kind.string?("é")
    true
    iex> Feel.Runtime.Kind.string?(<<0xFF>>)
    false
    iex> Feel.Runtime.Kind.string?(1)
    false

---

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