added new primitive combinator ‘hidden’

Added new primitive combinator ‘hidden p’ which hides “expected” tokens
in error message when parser ‘p’ fails.

CHANGELOG.md

@@ -89,6 +89,9 @@
 * Fixed bug with `notFollowedBy` always succeeded with parsers that don't
   consume input, see #6.
 
+* Added new primitive combinator `hidden p` which hides “expected” tokens in
+  error message when parser `p` fails.
+
 * Added comprehensive QuickCheck test suite.
 
 * Added benchmarks.

Text/Megaparsec.hs

@@ -65,6 +65,7 @@ module Text.Megaparsec
   , unexpected
   , (<?>)
   , label
+  , hidden
   , try
   , lookAhead
   , notFollowedBy

Text/Megaparsec/Prim.hs

@@ -31,6 +31,7 @@ module Text.Megaparsec.Prim
   , unexpected
   , (<?>)
   , label
+  , hidden
   , try
   , lookAhead
   , notFollowedBy
@@ -467,6 +468,12 @@ label p l = ParsecT $ \s cok cerr eok eerr ->
       eerr'    err = eerr $ setErrorMessage (Expected l) err
   in unParser p s cok' cerr eok' eerr'
 
+-- | @hidden p@ behaves just like parser @p@, but it doesn't show any “expected”
+-- tokens in error message when @p@ fails.
+
+hidden :: ParsecT s u m a -> ParsecT s u m a
+hidden p = label p ""
+
 -- | The parser @try p@ behaves like parser @p@, except that it
 -- pretends that it hasn't consumed any input when an error occurs.
 --