Why doesn't Haskell's Prelude.read return a Maybe?

Edit: As of GHC 7.6, readMaybe is available in the Text.Read module in the base package, along with readEither: http://hackage.haskell.org/packages/archive/base/latest/doc/html/Text-Read.html#v:readMaybe

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Great question! The type of read itself isn't changing anytime soon because that would break lots of things. However, there should be a maybeRead function.

Why isn't there? The answer is "inertia". There was a discussion in '08 which got derailed by a discussion over "fail."

The good news is that folks were sufficiently convinced to start moving away from fail in the libraries. The bad news is that the proposal got lost in the shuffle. There should be such a function, although one is easy to write (and there are zillions of very similar versions floating around many codebases).

See also this discussion.

Personally, I use the version from the safe package.

Yeah, it would be handy with a read function that returns Maybe. You can make one yourself:

readMaybe :: (Read a) => String -> Maybe a
readMaybe s = case reads s of
              [(x, "")] -> Just x
              _ -> Nothing

Apart from inertia and/or changing insights, another reason might be that it's aesthetically pleasing to have a function that can act as a kind of inverse of show. That is, you want that read . show is the identity (for types which are an instance of Show and Read) and that show . read is the identity on the range of show (i.e. show . read . show == show)

Having a Maybe in the type of read breaks the symmetry with show :: a -> String.