Make Doc values concatenable

Author: tarleb

src/Foreign/Lua/Module/DocLayout.hs

@@ -248,7 +248,9 @@ instance Peekable (Doc Text) where
 pushDoc :: Doc Text -> Lua ()
 pushDoc = Lua.pushAnyWithMetatable pushDocMT
   where
-    pushDocMT = Lua.ensureUserdataMetatable docTypeName $
+    pushDocMT = Lua.ensureUserdataMetatable docTypeName $ do
+      Lua.addfunction "__concat"   __concat
+      Lua.addfunction "__eq"       __eq
       Lua.addfunction "__tostring" __tostring
 
 instance Pushable (Doc Text) where
@@ -257,3 +259,11 @@ instance Pushable (Doc Text) where
 -- | Convert to string by rendering without reflowing.
 __tostring :: Doc Text -> Lua Text
 __tostring d = return $ Doc.render Nothing d
+
+-- | Concatenate two @'Doc'@.
+__concat :: Doc Text -> Doc Text -> Lua (Doc Text)
+__concat a b = return (a <> b)
+
+-- | Test @'Doc'@ equality.
+__eq :: Doc Text -> Doc Text -> Lua Bool
+__eq a b = return (a == b)

test/test-doclayout.lua

@@ -38,6 +38,17 @@ return {
       assert.are_equal(doclayout.render('hello world'), 'hello world')
     end),
 
+    test('equality', function ()
+      assert.is_truthy(doclayout.literal "true", doclayout.literal "true")
+    end),
+
+    test('concatenate docs', function ()
+      assert.are_equal(
+        tostring(doclayout.literal 'Rock-' .. doclayout.literal 'Ola'),
+       'Rock-Ola'
+      )
+    end),
+
     test('has tostring method', function ()
       local str = 'just a literal string for now'
       assert.are_equal(tostring(str), str)