= Proposal: make the $ operator left-associative =

== Arguments in favour ==

0) $ was introduced as a combinator for function application.
Therefore we might expect that whenever we have a function application
we can stick a $ in there. But this is not the case. Consider the
following expression:
{{{
f x y
}}}
There are two applications here and if $ behaved like function
application we would be able to write:
{{{
f $ x $ y
}}}
But as it is now this expression means something completely different.

(these following points taken from [http://www.haskell.org/pipermail/haskell-prime/2008-April/002459.html Dan Doel's post on the haskell-prime mailing list])

1) Anything of the form:

{{{
    f $ g $ h $ x
}}}

with right associative ($) can instead be written:

{{{
    f . g . h $ x
}}}
where the associativity of ($) doesn't matter. It's not uncommon to want to 
peel off the end of such a pipeline to eliminate a point. For the second 
form, such a translation is:
{{{
    \x -> f . g . h $ x ==> f . g . h
}}}
However:

{{{
    \x -> f $ g $ h $ x ==> f $ g $ h
}}}

Is invalid, so one might argue that writing such pipelines with composition is 
a better habit to get into, as it allows easier cleanup of code in this way 
(if you like somewhat point-free code, that is).

2) Left associative ($) allows you to eliminate more parentheses. Per #1, any 
parentheses eliminated by right associative ($) can be eliminated by (.) and 
a single ($). However, left associative ($) allows, for instance:

{{{
    f (g x) (h y) ==> f $ g x $ h y
}}}

3) Left associative ($) is consistent with left associative ($!). The right 
associative version of the latter is inconvenient, because it only allows 
things to be (easily) strictly applied to the last argument of a function. 
Needing to strictly apply to other arguments gives rise to things like:

{{{
   (f $! x) y z
   ((f $! x) $! y) $! z
}}}

Left associative, these are:

{{{
   f $! x $ y $ z
   f $! x $! y $! z
}}}

There may be more arguments, but those are the ones I've heard that I can 
think of at the moment. #3 strikes me as the most likely to bite people (the 
other two are more stylistic issues), but I suppose I don't know the relative 
frequency of strict pipelines (f $! g $! x) versus strict applications at 
non-final arguments.

== Arguments against ==

 * This would break a ''lot'' of code.