From 3743b0e40651db49eb9adec1252f934dd7d45bbb Mon Sep 17 00:00:00 2001
From: Marcel Otto <marcelotto@gmx.de>
Date: Wed, 27 May 2020 23:55:43 +0200
Subject: [PATCH] Add RDF.Literal.is_a?/2

---
 lib/rdf/literal.ex         | 15 +++++++++++++++
 test/unit/literal_test.exs | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/lib/rdf/literal.ex b/lib/rdf/literal.ex
index 8cc9280..3311d26 100644
--- a/lib/rdf/literal.ex
+++ b/lib/rdf/literal.ex
@@ -167,6 +167,21 @@ defmodule RDF.Literal do
   """
   defdelegate datatype?(value), to: RDF.Literal.Datatype.Registry, as: :datatype?
 
+  @doc """
+  Checks if 'literal' is literal with the given `datatype`.
+
+  `datatype` can be one of the following:
+
+  - a `RDF.Literal.Datatype` module  which checks if the literal is of this datatype or derived from it
+  - `RDF.XSD.Numeric` which checks if the literal is one of the numeric XSD datatypes or derived of one of them
+  - `RDF.XSD.Datatype` which checks if the literal is a XSD datatype or derived of one of them
+
+  """
+  def is_a?(literal, RDF.XSD.Numeric), do: RDF.XSD.Numeric.datatype?(literal)
+  def is_a?(literal, RDF.XSD.Datatype), do: RDF.XSD.datatype?(literal)
+  def is_a?(literal, RDF.Literal.Datatype), do: datatype?(literal)
+  def is_a?(literal, datatype), do: datatype?(datatype) and datatype.datatype?(literal)
+
   @doc """
   Returns if the literal uses the `RDF.Literal.Generic` datatype or on of the dedicated builtin or custom `RDF.Literal.Datatype`s.
   """
diff --git a/test/unit/literal_test.exs b/test/unit/literal_test.exs
index 3c45119..060288e 100644
--- a/test/unit/literal_test.exs
+++ b/test/unit/literal_test.exs
@@ -191,6 +191,44 @@ defmodule RDF.LiteralTest do
     end
   end
 
+  describe "is_a?/2" do
+    test "with RDF.Literal.Datatype module" do
+      assert ~L"foo" |> Literal.is_a?(XSD.String)
+      assert ~L"foo"en |> Literal.is_a?(RDF.LangString)
+      assert XSD.integer(42) |> Literal.is_a?(XSD.Integer)
+      assert XSD.byte(42) |> Literal.is_a?(XSD.Integer)
+      assert RDF.literal("foo", datatype: "http://example.com/dt") |> RDF.Literal.is_a?(RDF.Literal.Generic)
+      refute XSD.float(3.14) |> Literal.is_a?(XSD.Integer)
+    end
+
+    test "with XSD.Numeric" do
+      assert XSD.integer(42) |> Literal.is_a?(XSD.Numeric)
+      assert XSD.byte(42) |> Literal.is_a?(XSD.Numeric)
+      assert XSD.decimal(3.14) |> Literal.is_a?(XSD.Numeric)
+      refute ~L"foo" |> Literal.is_a?(XSD.Numeric)
+      refute ~L"foo"en |> Literal.is_a?(XSD.Numeric)
+    end
+
+    test "with XSD.Datatype" do
+      assert XSD.integer(42) |> Literal.is_a?(XSD.Datatype)
+      assert XSD.byte(42) |> Literal.is_a?(XSD.Datatype)
+      assert XSD.decimal(3.14) |> Literal.is_a?(XSD.Datatype)
+      assert ~L"foo" |> Literal.is_a?(XSD.Datatype)
+      refute ~L"foo"en |> Literal.is_a?(XSD.Datatype)
+    end
+
+    test "with non-datatype modules" do
+      refute ~L"foo" |> Literal.is_a?(String)
+      refute ~L"foo" |> Literal.is_a?(Regex)
+      refute XSD.integer(42) |> Literal.is_a?(Integer)
+    end
+
+    test "with non-literal" do
+      refute "foo" |> Literal.is_a?(XSD.String)
+      refute 42 |> Literal.is_a?(XSD.Numeric)
+    end
+  end
+
   describe "has_datatype?" do
     Enum.each literals(~W[all_simple all_plain_lang]a), fn literal ->
       @tag literal: literal