Just a quickie:
I see that the fixity decl of the monad operation >> and >>= changed
from right associative in 1.3 to left associative in 1.4. This strikes
me as a bug in 1.4 which ought to be reversed in 98.
Right associativity allows:
f >>= \x->
g >>= \y->
h x
which with left associativity will be rejected because x is unbound
(in h x), or even worse: if x is bound at an outer scope, you might get
completely the wrong value (or if you're lucky a type error).
I haven't been able to find any archived messages motivating the
change for 1.4: am I missing something important?
I can only imagine two reasons for left associativity:
1. To make the >>= syntax so horrible in the common case (by requiring
brackets or $ signs) that everyone moves to `do' notation. :-)
2. To allow a sort of "unix pipeline" style of monadic composition,
where the components don't have explicit lambdas:
f >>= g >>= h >>= j
I would argue that this is an infrequent style compared to the
common case of my first example. In any case, with the new (=<<)
operator, the "pipeline" composition can easily be cast to look
more like normal functional composition anyway,
j =<< h =<< g =<< f
removing the need for >>= to be left associative.
What do other people think?
Regards,
Malcolm
