Fix the interaction of layout and parens

The layout processor didn't account for layout blocks that were terminated by
parens or braces, so this accounts for that in the context stack that is kept by
the layout processor.  Fixes #81

src/Cryptol/Parser/LexerUtils.hs

@@ -204,6 +204,15 @@ dropWhite = filter (notWhite . tokenType . thing)
         notWhite _         = True
 
 
+data Block = Virtual Int     -- ^ Virtual layout block
+           | Explicit TokenT -- ^ An explicit layout block, expecting this ending
+                             -- token.
+             deriving (Show)
+
+isVirtual :: Block -> Bool
+isVirtual Virtual {} = True
+isVirtual _          = False
+
 -- Add separators computed from layout
 layout :: Config -> [Located Token] -> [Located Token]
 layout cfg ts0
@@ -227,6 +236,22 @@ layout cfg ts0
     -- If we find the EOF, we close all open blocks, and then we stop.
     | EOF   <- ty = extra ++ [ virt cfg (to pos) VCurlyR | _ <- stack ] ++ [t]
 
+    -- Left parens and braces start new explicit blocks
+    | Sym ParenL <- ty = t : loop False (Explicit (Sym ParenR) : stack) ts
+    | Sym CurlyL <- ty = t : loop False (Explicit (Sym CurlyR) : stack) ts
+
+    -- Right parens and braces close to the nearest explicit block, failing if
+    -- they don't properly close it
+    | Sym ParenR <- ty
+    , Explicit (Sym ParenR) : ps' <- ps = [ virt cfg (to pos) VCurlyR | _ <- es ]
+                                       ++ t
+                                        : loop False ps' ts
+
+    | Sym CurlyR <- ty
+    , Explicit (Sym CurlyR) : ps' <- ps = [ virt cfg (to pos) VCurlyR | _ <- es ]
+                                       ++ t
+                                        : loop False ps' ts
+
     -- If we see the keyword `where`, we start a new virtual block
     | KW KW_where <- ty = t : virt cfg (to pos) VCurlyL
                             : loop True stack ts
@@ -245,10 +270,12 @@ layout cfg ts0
           punc | startBlock = []
                | otherwise  = [virt cfg (to pos) VSemi]
 
+          (es,ps) = span isVirtual stack
+
   -- We are the first token in a new block, push our column on the stack.
   loop True ps (t : ts) = t : extra ++ loop startBlock ps' ts
     where
-    ps' = c : ps
+    ps' = Virtual c : ps
     c   = col (from (srcRange t))
     pos = srcRange t
 
@@ -257,12 +284,12 @@ layout cfg ts0
       | otherwise                            = (False,[])
 
   -- We are not the first token in a block, check for virtual punctuation.
-  loop False (p : ps) (t : ts)
+  loop False ps@(Virtual p : ps') (t : ts)
     | col pos == p  = virt cfg pos VSemi        -- same indent: add semi
                     : t
-                    : loop False (p : ps) ts
+                    : loop False ps ts
     | col pos < p   = virt cfg pos VCurlyR      -- less indent: add }
-                    : loop False ps (t : ts)
+                    : loop False ps' (t : ts)
       where
       pos   = from (srcRange t)