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

The `instance of` operator (DMN 1.6, Table 62).

`value instance of type` is `true` when the value is an instance of the type and `false` when
it is not. It is a question with an answer for every value, so it is never `null` and it cannot
report anything: the function returns the boolean and not an `t:Feel.Runtime.Env.outcome/0`.

The type is a resolved `t:Feel.Type.t/0`. The analyzer resolves it against the scope. A type that
cannot be resolved (a name that is not defined) makes the result `null`, as the first step of
Table 62 says, and the node carries that error: it never gets here.

Nothing is converted: a singleton list is not an instance of the type of its element.
`null` is an instance of `Null` and of no other type, not even `Any` (D-23); that is the one
place where `instance of` differs from conformance, and `Feel.Type.Instance.instance?/2` has it.

# `instance_of`

```elixir
@spec instance_of(Feel.Value.t(), Feel.Type.t()) :: boolean()
```

Returns whether `value` is an instance of `type`.

    iex> Feel.Runtime.TypeCheck.instance_of(Decimal.new(1), :number)
    true
    iex> Feel.Runtime.TypeCheck.instance_of(Decimal.new(1), {:list, :number})
    false
    iex> Feel.Runtime.TypeCheck.instance_of([Decimal.new(1)], {:list, :number})
    true
    iex> Feel.Runtime.TypeCheck.instance_of(nil, :null)
    true
    iex> Feel.Runtime.TypeCheck.instance_of(nil, :any)
    false

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