rdf-ex/lib/rdf/literal.ex

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defmodule RDF.Literal do
@moduledoc """
RDF literals are leaf nodes of a RDF graph containing raw data, like strings and numbers.
"""
defstruct [:value, :uncanonical_lexical, :datatype, :language]
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@type t :: module
alias RDF.Datatype.NS.XSD
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# to be able to pattern-match on plain types; we can't use RDF.Literal.Guards here since these aren't compiled here yet
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@xsd_string XSD.string
@lang_string RDF.iri("http://www.w3.org/1999/02/22-rdf-syntax-ns#langString")
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@plain_types [@xsd_string, @lang_string]
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@doc """
Creates a new `RDF.Literal` of the given value and tries to infer an appropriate XSD datatype.
Note: The `RDF.literal` function is a shortcut to this function.
The following mapping of Elixir types to XSD datatypes is applied:
| Elixir datatype | XSD datatype |
| :-------------- | :------------- |
| `string` | `xsd:string` |
| `boolean` | `xsd:boolean` |
| `integer` | `xsd:integer` |
| `float` | `xsd:double` |
| `Time` | `xsd:time` |
| `Date` | `xsd:date` |
| `DateTime` | `xsd:dateTime` |
| `NaiveDateTime` | `xsd:dateTime` |
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## Examples
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iex> RDF.Literal.new(42)
%RDF.Literal{value: 42, datatype: XSD.integer}
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"""
def new(value)
def new(%RDF.Literal{} = literal), do: literal
def new(value) when is_binary(value), do: RDF.String.new(value)
def new(value) when is_boolean(value), do: RDF.Boolean.new(value)
def new(value) when is_integer(value), do: RDF.Integer.new(value)
def new(value) when is_float(value), do: RDF.Double.new(value)
def new(%Date{} = value), do: RDF.Date.new(value)
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def new(%Time{} = value), do: RDF.Time.new(value)
def new(%DateTime{} = value), do: RDF.DateTime.new(value)
def new(%NaiveDateTime{} = value), do: RDF.DateTime.new(value)
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def new(value) do
raise RDF.Literal.InvalidError, "#{inspect value} not convertible to a RDF.Literal"
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end
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@doc """
Creates a new `RDF.Literal` with the given datatype or language tag.
"""
def new(value, opts)
def new(value, opts) when is_list(opts),
do: new(value, Map.new(opts))
def new(value, %{language: nil} = opts),
do: new(value, Map.delete(opts, :language))
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def new(value, %{language: _} = opts) do
if is_binary(value) do
if opts[:datatype] in [nil, @lang_string] do
RDF.LangString.new(value, opts)
else
raise ArgumentError, "datatype with language must be rdf:langString"
end
else
new(value, Map.delete(opts, :language)) # Should we raise a warning?
end
end
def new(value, %{datatype: %RDF.IRI{} = id} = opts) do
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case RDF.Datatype.get(id) do
nil -> %RDF.Literal{value: value, datatype: id}
datatype -> datatype.new(value, opts)
end
end
def new(value, %{datatype: datatype} = opts),
do: new(value, %{opts | datatype: RDF.iri(datatype)})
def new(value, opts) when is_map(opts) and map_size(opts) == 0,
do: new(value)
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@doc """
Creates a new `RDF.Literal`, but fails if it's not valid.
Note: Validation is only possible if an `RDF.Datatype` with an implementation of
`RDF.Datatype.valid?/1` exists.
## Examples
iex> RDF.Literal.new!("3.14", datatype: XSD.double) == RDF.Literal.new("3.14", datatype: XSD.double)
true
iex> RDF.Literal.new!("invalid", datatype: "http://example/unkown_datatype") == RDF.Literal.new("invalid", datatype: "http://example/unkown_datatype")
true
iex> RDF.Literal.new!("foo", datatype: XSD.integer)
** (RDF.Literal.InvalidError) invalid RDF.Literal: %RDF.Literal{value: nil, lexical: "foo", datatype: ~I<http://www.w3.org/2001/XMLSchema#integer>}
iex> RDF.Literal.new!("foo", datatype: RDF.langString)
** (RDF.Literal.InvalidError) invalid RDF.Literal: %RDF.Literal{value: "foo", datatype: ~I<http://www.w3.org/1999/02/22-rdf-syntax-ns#langString>, language: nil}
"""
def new!(value, opts \\ %{}) do
with %RDF.Literal{} = literal <- new(value, opts) do
if valid?(literal) do
literal
else
raise RDF.Literal.InvalidError, "invalid RDF.Literal: #{inspect literal}"
end
else
invalid ->
raise RDF.Literal.InvalidError, "invalid result of RDF.Literal.new: #{inspect invalid}"
end
end
@doc """
Returns the lexical representation of the given literal according to its datatype.
"""
def lexical(%RDF.Literal{value: value, uncanonical_lexical: nil, datatype: id} = literal) do
case RDF.Datatype.get(id) do
nil -> to_string(value)
datatype -> datatype.lexical(literal)
end
end
def lexical(%RDF.Literal{uncanonical_lexical: lexical}), do: lexical
@doc """
Returns the given literal in its canonical lexical representation.
"""
def canonical(%RDF.Literal{uncanonical_lexical: nil} = literal), do: literal
def canonical(%RDF.Literal{datatype: id} = literal) do
case RDF.Datatype.get(id) do
nil -> literal
datatype -> datatype.canonical(literal)
end
end
@doc """
Returns if the given literal is in its canonical lexical representation.
"""
def canonical?(%RDF.Literal{uncanonical_lexical: nil}), do: true
def canonical?(_), do: false
@doc """
Returns if the value of the given literal is a valid according to its datatype.
"""
def valid?(%RDF.Literal{datatype: id} = literal) do
case RDF.Datatype.get(id) do
nil -> true
datatype -> datatype.valid?(literal)
end
end
@doc """
Returns if a literal is a simple literal.
A simple literal has no datatype or language.
see <http://www.w3.org/TR/sparql11-query/#simple_literal>
"""
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def simple?(%RDF.Literal{datatype: @xsd_string}), do: true
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def simple?(_), do: false
@doc """
Returns if a literal is a language-tagged literal.
see <http://www.w3.org/TR/rdf-concepts/#dfn-plain-literal>
"""
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def has_language?(%RDF.Literal{datatype: @lang_string}), do: true
def has_language?(_), do: false
@doc """
Returns if a literal is a datatyped literal.
For historical reasons, this excludes `xsd:string` and `rdf:langString`.
see <http://www.w3.org/TR/rdf-concepts/#dfn-typed-literal>
"""
def has_datatype?(literal) do
not plain?(literal) and not has_language?(literal)
end
@doc """
Returns if a literal is a plain literal.
A plain literal may have a language, but may not have a datatype.
For all practical purposes, this includes `xsd:string` literals too.
see <http://www.w3.org/TR/rdf-concepts/#dfn-plain-literal>
"""
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def plain?(%RDF.Literal{datatype: datatype})
when datatype in @plain_types, do: true
def plain?(_), do: false
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def typed?(literal), do: not plain?(literal)
@doc """
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Checks if two `RDF.Literal`s are equal.
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Non-RDF terms are tried to be coerced via `RDF.Term.coerce/1` before comparison.
Returns `nil` when the given arguments are not comparable as Literals.
see <https://www.w3.org/TR/rdf-concepts/#section-Literal-Equality>
"""
def equal_value?(left, right)
def equal_value?(%RDF.Literal{datatype: id1} = literal1, %RDF.Literal{datatype: id2} = literal2) do
case RDF.Datatype.get(id1) do
nil ->
if id1 == id2 do
literal1.value == literal2.value
end
datatype ->
datatype.equal_value?(literal1, literal2)
end
end
# TODO: Handle AnyURI in its own RDF.Datatype implementation
@xsd_any_uri "http://www.w3.org/2001/XMLSchema#anyURI"
def equal_value?(%RDF.Literal{datatype: %RDF.IRI{value: @xsd_any_uri}} = left, right),
do: RDF.IRI.equal_value?(left, right)
def equal_value?(left, %RDF.Literal{datatype: %RDF.IRI{value: @xsd_any_uri}} = right),
do: RDF.IRI.equal_value?(left, right)
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def equal_value?(%RDF.Literal{} = left, right) when not is_nil(right) do
unless RDF.Term.term?(right) do
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equal_value?(left, RDF.Term.coerce(right))
end
end
def equal_value?(_, _), do: nil
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@doc """
Checks if the first of two `RDF.Literal`s is smaller then the other.
Returns `nil` when the given arguments are not comparable datatypes.
"""
def less_than?(literal1, literal2) do
case compare(literal1, literal2) do
:lt -> true
nil -> nil
_ -> false
end
end
@doc """
Checks if the first of two `RDF.Literal`s is greater then the other.
Returns `nil` when the given arguments are not comparable datatypes.
"""
def greater_than?(literal1, literal2) do
case compare(literal1, literal2) do
:gt -> true
nil -> nil
_ -> false
end
end
@doc """
Compares two `RDF.Literal`s.
Returns `:gt` if first literal is greater than the second in terms of their datatype
and `:lt` for vice versa. If the two literals are equal `:eq` is returned.
For datatypes with only partial ordering `:indeterminate` is returned when the
order of the given literals is not defined.
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Returns `nil` when the given arguments are not comparable datatypes.
"""
def compare(left, right)
def compare(%RDF.Literal{datatype: id1} = literal1, %RDF.Literal{datatype: id2} = literal2) do
case RDF.Datatype.get(id1) do
nil ->
if id1 == id2 do
cond do
literal1.value == literal2.value -> :eq
literal1.value < literal2.value -> :lt
true -> :gt
end
end
datatype ->
datatype.compare(literal1, literal2)
end
end
def compare(_, _), do: nil
end
defimpl String.Chars, for: RDF.Literal do
def to_string(literal) do
RDF.Literal.lexical(literal)
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end
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end