Parse parentheses

Yes, it's that easy. Try out the difference between
1 * 2 + 3
and
1 * (2 + 3)

diff --git a/AST.hs b/AST.hs
index 7dad3a19e91eab9f12657101bd224b5c81742d07..e491b648a7d45f7bd3b419b0e3ff6a8c215cbd83 100644 (file)
--- a/AST.hs
+++ b/AST.hs
@@ -13,7 +13,7 @@ data BinOp = Add | Sub | Mul | Cmp Ordering
   deriving Show
 
 instance Read Expr where
-  readPrec = choice [ parseNum
+  readPrec = parens $ choice [ parseNum
                              , parseVar
                              , parseBinOp "<" 10 (Cmp LT)
                              , parseBinOp "+" 20 Add