Merge pull request #408 from github/extract-diff

Create a diff function and clarify the role of printDiff

app/Main.hs

@@ -7,6 +7,7 @@ import qualified Parsers as P
 import Syntax
 import Range
 import qualified PatchOutput
+import Renderer
 import Split
 import Term
 import Unified
@@ -47,29 +48,28 @@ main = do
   let parse = (P.parserForType . T.pack . takeExtension) sourceAPath
   terms <- sequence $ parse <$> sources
   let replaceLeaves = breakDownLeavesByWord <$> sources
-  printDiff arguments (runJoin sources) (runJoin $ replaceLeaves <*> terms)
+  printDiff arguments (uncurry diff $ runJoin $ replaceLeaves <*> terms) (runJoin sources)
   where opts = info (helper <*> arguments)
           (fullDesc <> progDesc "Diff some things" <> header "semantic-diff - diff semantically")
 
--- | Print a diff, given the command-line arguments, source files, and terms.
-printDiff :: Arguments -> (Source Char, Source Char) -> (Term T.Text Info, Term T.Text Info) -> IO ()
-printDiff arguments (aSource, bSource) (aTerm, bTerm) = case format arguments of
-  Unified -> do
-    rendered <- unified diff aSource bSource
-    B1.putStr rendered
-  Split -> do
-    rendered <- split diff aSource bSource
-    case output arguments of
-      Just path -> do
+-- | Diff two terms.
+diff :: (Eq a, Eq annotation, Categorizable annotation) => Term a annotation -> Term a annotation -> Diff a annotation
+diff = interpret comparable
+
+-- | Return a renderer from the command-line arguments that will print the diff.
+printDiff :: Arguments -> Renderer T.Text (IO ())
+printDiff arguments diff sources = case format arguments of
+  Unified -> B1.putStr =<< unified diff sources
+  Split -> put (output arguments) =<< split diff sources
+    where
+      put Nothing rendered = TextIO.putStr rendered
+      put (Just path) rendered = do
         isDir <- doesDirectoryExist path
         let outputPath = if isDir
                          then path </> (takeFileName (sourceB arguments) -<.> ".html")
                          else path
-        IO.withFile outputPath IO.WriteMode (write rendered)
-      Nothing -> TextIO.putStr rendered
-  Patch -> putStr $ PatchOutput.patch diff aSource bSource
-  where diff = interpret comparable aTerm bTerm
-        write rendered h = TextIO.hPutStr h rendered
+        IO.withFile outputPath IO.WriteMode (flip TextIO.hPutStr rendered)
+  Patch -> putStr $ PatchOutput.patch diff sources
 
 -- | Replace every string leaf with leaves of the words in the string.
 breakDownLeavesByWord :: Source Char -> Term T.Text Info -> Term T.Text Info

src/PatchOutput.hs

@@ -17,7 +17,7 @@ import Data.Maybe
 import Data.Monoid
 
 patch :: Renderer a String
-patch diff sourceA sourceB = mconcat $ showHunk (sourceA, sourceB) <$> hunks diff (sourceA, sourceB)
+patch diff (sourceA, sourceB) = mconcat $ showHunk (sourceA, sourceB) <$> hunks diff (sourceA, sourceB)
 
 data Hunk a = Hunk { offset :: (Sum Int, Sum Int), changes :: [Change a], trailingContext :: [Row a] }
   deriving (Eq, Show)

src/Renderer.hs

@@ -4,4 +4,4 @@ import Diff
 import Source
 
 -- | A function that will render a diff, given the two source files.
-type Renderer a b = Diff a Info -> Source Char -> Source Char -> b
+type Renderer a b = Diff a Info -> (Source Char, Source Char) -> b

src/Split.hs

@@ -32,7 +32,7 @@ classifyMarkup :: Foldable f => f String -> Markup -> Markup
 classifyMarkup categories element = maybe element ((element !) . A.class_ . stringValue . ("category-" ++)) $ maybeFirst categories
 
 split :: Renderer leaf (IO TL.Text)
-split diff before after = return . renderHtml
+split diff (before, after) = return . renderHtml
   . docTypeHtml
     . ((head $ link ! A.rel "stylesheet" ! A.href "style.css") <>)
     . body

src/Unified.hs

@@ -15,7 +15,7 @@ import qualified Data.OrderedMap as Map
 import Rainbow
 
 unified :: Renderer a (IO ByteString)
-unified diff before after = do
+unified diff (before, after) = do
   renderer <- byteStringMakerFromEnvironment
   return . mconcat . chunksToByteStrings renderer . fst $ iter g mapped where
     mapped = fmap (unifiedPatch &&& range) diff