Subtyping: SA-Arrow

computationclub · Oct 10, 2017 · 3577e2641b2723b2beb606830e8df0d8d223ad0a · 3577e26
1 parent a4a7b67
commit 3577e2641b2723b2beb606830e8df0d8d223ad0a
Unified Split

Showing with 28 additions and 0 deletions.

+6 −0 lib/simple_types.rb

+22 −0 spec/simple_types_spec.rb
diff --git a/lib/simple_types.rb b/lib/simple_types.rb
@@ -9,6 +9,12 @@ def subtype_of?(subtype, supertype)
      subtype.members.key?(field) && subtype_of?(subtype.members[field], type)
    end
  end
+  if subtype.is_a?(Type::Function) && supertype.is_a?(Type::Function)
+    return (
+      subtype_of?(supertype.from, subtype.from) &&
+      subtype_of?(subtype.to, supertype.to)
+    )
+  end
  false
 end

diff --git a/spec/simple_types_spec.rb b/spec/simple_types_spec.rb
@@ -51,6 +51,28 @@
    end
  end

+  describe 'SA-ARROW' do
+    specify do
+      expect('Bool -> Bool').to be_subtype_of('Bool -> Bool')
+    end
+
+    specify do
+      expect('Bool -> Bool').to be_subtype_of('Bool -> Top')
+    end
+
+    specify do
+      expect('Top -> Bool').to be_subtype_of('Bool -> Bool')
+    end
+
+    specify do
+      expect('Bool -> Top').not_to be_subtype_of('Bool -> Bool')
+    end
+
+    specify do
+      expect('Bool -> Bool').not_to be_subtype_of('Top -> Bool')
+    end
+  end
+
  def expr(text)
    Parser.parse(text)
  end