Re: [Haskell-cafe] ANN: rematch, an library for composable assertions with human readable failure messages

On Tue, Apr 16, 2013 at 10:17:48AM +0100, Tom Crayford wrote:

The core API is very simple:

data Matcher a = Matcher { match :: a -> Bool -- ^ A function that returns True if the matcher should pass, False if it should fail , description :: String -- ^ A description of the matcher (usually of its success conditions) , describeMismatch :: a -> String -- ^ A description to be shown if the match fails. }

How about combining match and describeMismatch as a single function of type a -> Match? Then you wouldn't need the precondition on describeMismatch. Defining a Monoid instance for Match might also be useful.