C. McCann wrote:
Heinrich Apfelmus wrote:
Combined with >>= / >> you have multiple reading direction in the same
expression, as in
expression ( c . b . a ) `liftM` a1 >>= a2 >>= a3
reading order 6 5 4 1 2 3
That's why I'm usually using =<< instead of >>= .
Does it bother you that (=<<) is defined to be infixr 1, while (<$>)
and (<*>) are infixl 4? Or is that just me?
For instance, I might write the above expression as something like:
a3 =<< a2 =<< a . b . c <$> a1
>
But this still seems awkward, because it mixes different fixities and
I have to mentally regroup things when reading it. Right associativity
here does make a certain amount of sense for monads, but
left-associativity is consistent with plain function application and
feels more natural to me.
Well, you can't give (=<<) left fixity because its type doesn't allow it.
(a3 =<< a2) =<< a1 -- ill-typed!
So, (=<<) is modeled after (:) , not after (<$>) .
Regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
