rdf-ex/lib/rdf/blank_node.ex
2021-01-13 16:55:24 +01:00

64 lines
1.6 KiB
Elixir

defmodule RDF.BlankNode do
@moduledoc """
An RDF blank node (aka bnode) is a local node of a graph without an IRI.
see <https://www.w3.org/TR/rdf11-primer/#section-blank-node>
and <https://www.w3.org/TR/rdf11-concepts/#section-blank-nodes>
"""
@type t :: %__MODULE__{
value: String.t()
}
@enforce_keys [:value]
defstruct [:value]
@doc """
Creates a `RDF.BlankNode`.
"""
@spec new :: t
def new, do: new(:erlang.unique_integer([:positive]))
@doc """
Creates a `RDF.BlankNode` with a user-defined value for its identity.
## Examples
iex> RDF.bnode(:foo)
%RDF.BlankNode{value: "foo"}
"""
@spec new(reference | String.t() | atom | integer) :: t
def new(value)
def new(string) when is_binary(string), do: %__MODULE__{value: string}
def new(atom) when is_atom(atom), do: atom |> to_string() |> new()
def new(integer) when is_integer(integer), do: new("b#{integer}")
def new(ref) when is_reference(ref) do
"#Ref<" <> value = ref |> :erlang.ref_to_list() |> to_string()
value |> String.trim_trailing(">") |> new()
end
@doc """
Returns the internal string representation of a blank node.
"""
def value(%__MODULE__{} = bnode), do: bnode.value
@doc """
Tests for value equality of blank nodes.
Returns `nil` when the given arguments are not comparable as blank nodes.
"""
@spec equal_value?(t, t) :: boolean | nil
def equal_value?(left, right)
def equal_value?(%__MODULE__{value: left}, %__MODULE__{value: right}),
do: left == right
def equal_value?(_, _),
do: nil
defimpl String.Chars do
def to_string(bnode), do: "_:#{bnode.value}"
end
end