Functor => Applicative => Monad

John Smith voldermort at
Mon Dec 6 19:22:28 CET 2010

On 06/12/2010 17:47, Stephen Tetley wrote:
> Me thinks there's more value that "the next language after Haskell"
> might have such a hierarchy than Haskell itself.
> At Haskell 1.3 I think there was one text book (Davie), possibly none
> at Haskell 1.4 and many at Haskell 98. The value of invalidating 12 or
> so years of documentation for "logic" seems somewhat questionable from
> my perspective. If either proposal were limited to just adding class
> constraints to get the desired hierarchy rather than eliminating
> methods, they might have more legs...

.NET and Java are used in billions of line of production code and have thousands of books written about them, but new 
versions often obsolete what would have previously been recommended practice. Breaking legacy documentation is generally 
the least of anyone's worries when moving a language forward.

As for breaking code, new versions of GHC often break a bunch of packages (see the build logs on hackage), although the 
breakage would be more pervasive in this case.

As for eliminating methods, I'm only proposing that they be moved into a legacy module (as was done with old-time and 
OldException), so the classic functions will still be available.

More information about the Libraries mailing list