Allow doctests to span multiple lines with a trailing \ like the REPL…

… already supports (#1757)

* Allow doctests to span multiple lines with a trailing \ like the REPL already supports
* Empty doctest lines to be skipped without error

src/Cryptol/REPL/Command.hs

@@ -2062,10 +2062,12 @@ data SubcommandResult = SubcommandResult
 checkBlock ::
   [T.Text] {- ^ lines of the code block -} ->
   REPL [SubcommandResult]
-checkBlock = isolated . go
+checkBlock = isolated . go . continuedLines
   where
     go [] = pure []
-    go (line:block) =
+    go (line:block)
+      | T.all isSpace line = go block
+      | otherwise =
       case parseCommand (findNbCommand True) (T.unpack line) of
         Nothing -> do
           pure [SubcommandResult
@@ -2104,6 +2106,19 @@ checkBlock = isolated . go
               subresults <- checkBlock block
               pure (subresult : subresults)
 
+-- | Combine lines ending in a backslash with the next line.
+continuedLines :: [T.Text] -> [T.Text]
+continuedLines xs =
+  case span ("\\" `T.isSuffixOf`) xs of
+    ([], []) -> []
+    (a, []) -> [concat' (map T.init a)] -- permissive
+    (a, b:bs) -> concat' (map T.init a ++ [b]) : continuedLines bs
+  where
+    -- concat that eats leading whitespace between elements
+    concat' [] = T.empty
+    concat' (y:ys) = T.concat (y : map (T.dropWhile isSpace) ys)
+
+
 captureLog :: REPL a -> REPL (String, a)
 captureLog m = do
   previousLogger <- getLogger

tests/docstrings/T02.cry

@@ -31,7 +31,9 @@ submodule F7 = submodule F where
 /**
  ** ```repl
  ** let y = 20
- ** :check f 10 == 20
+ **
+ ** :check f 10 \
+ **          == 20
  ** ``` */
 f : Integer -> Integer
 f x = x + x