further reduce newlines for compact output (cdepillabout#84)

added a doctest for a simple Value type

src/Text/Pretty/Simple.hs

@@ -680,6 +680,12 @@ layoutStringAnsi opts = fmap convertStyle . layoutString opts
 --         , B
 --             ( B ( B A ) ) ] )
 --
+-- >>> data Value = ValueStruct [(String,Value)] | ValueInt Int deriving Show
+--
+-- >>> pPrintOpt CheckColorTty defaultOutputOptionsDarkBg {outputOptionsCompact = True} $ ValueStruct [("id", ValueInt 123), ("state", ValueInt 1)]
+-- ValueStruct
+--     [ ( "id", ValueInt 123 ), ( "state", ValueInt 1 ) ]
+--
 -- __Initial indent__
 --
 -- >>> pPrintOpt CheckColorTty defaultOutputOptionsDarkBg {outputOptionsInitialIndent = 3} $ B ( B ( B ( B A ) ) )

src/Text/Pretty/Simple/Internal/Printer.hs

@@ -255,7 +255,10 @@ prettyExpr opts = (if outputOptionsCompact opts then group else id) . \case
             spaceIfNeeded = \case
               Other (' ' : _) : _ -> mempty
               _ -> space
-    lineAndCommaSep x y = x <> line' <> annotate Comma "," <> y
+    lineAndCommaSep x y =
+      if outputOptionsCompact opts
+      then x <> annotate Comma "," <> y
+      else x <> line' <> annotate Comma "," <> y
 
 -- | Determine whether this expression should be displayed on a single line.
 isSimple :: Expr -> Bool