Fix RDF.resource?/1 to not fail when called with unresolvable atoms

CHANGELOG.md

@@ -33,6 +33,8 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 ### Changed
 
 - Elixir versions < 1.6 are no longer supported
+- `RDF.resource?/1` does not fail anymore when called with unresolvable atoms 
+  but returns `false` instead
 - `RDF.String.new/2` and `RDF.String.new!/2` produce a `rdf:langString` when 
   given a language tag
 - `RDF.IRI.absolute/2` returns `nil` if the given base is not absolute, instead 

lib/rdf.ex

@@ -55,10 +55,16 @@ defmodule RDF do
 
   ## Examples
 
+  Supposed `EX` is a `RDF.Vocabulary.Namespace` and `Foo` is not.
+
       iex> RDF.resource?(RDF.iri("http://example.com/resource"))
       true
       iex> RDF.resource?(EX.resource)
       true
+      iex> RDF.resource?(EX.Resource)
+      true
+      iex> RDF.resource?(Foo.Resource)
+      false
       iex> RDF.resource?(RDF.bnode)
       true
       iex> RDF.resource?(RDF.integer(42))
@@ -69,8 +75,12 @@ defmodule RDF do
   def resource?(value)
   def resource?(%IRI{}),                  do: true
   def resource?(%BlankNode{}),            do: true
-  def resource?(atom) when is_atom(atom) and atom not in ~w[true false nil]a,
-      do: resource?(Namespace.resolve_term(atom))
+  def resource?(atom) when is_atom(atom) and atom not in ~w[true false nil]a do
+    resource?(Namespace.resolve_term(atom))
+  rescue
+    RDF.Namespace.UndefinedTermError -> false
+  end
+
   def resource?(_),                       do: false
 
   @doc """
@@ -78,10 +88,16 @@ defmodule RDF do
 
   ## Examples
 
+  Supposed `EX` is a `RDF.Vocabulary.Namespace` and `Foo` is not.
+
       iex> RDF.term?(RDF.iri("http://example.com/resource"))
       true
       iex> RDF.term?(EX.resource)
       true
+      iex> RDF.term?(EX.Resource)
+      true
+      iex> RDF.term?(Foo.Resource)
+      false
       iex> RDF.term?(RDF.bnode)
       true
       iex> RDF.term?(RDF.integer(42))