G'day all.
On Thu, Jul 17, 2003 at 05:21:47PM +0200, Christian Maeder wrote:
> Why do you outrule other useful libraries (see above). In fact ($) is
> quite cryptic (for a non-Haskeller).
Actually this gives me a perfect opportunity to rant a bit. :-)
($) is a wart, even for a Haskeller. It has the correct meaning and
the correct precedence, but it has the wrong associativity. "Normal"
application is left-associative. There's no reason why ($) shouldn't
be either.
Of course, sometimes you want right-associative apply, but there's
already a simple way to do this. If you want to write:
f (g (h (i x)))
you can use this:
f . g . h . i $ x
But there is no way to write this parenthesis-free:
f (g x) (h y) (i z)
Now it's arguable that this is clearer with the parentheses, and I
would agree with that. However, consider the situation with ($!).
When you use strict-apply, you intend that one or more of the arguments
to some function is/are to be strictly evaluated. Making ($!)
right-associative only gives you _exactly_ one, and it's always the
rightmost one, which gives it a 1-in-n chance of being right for a
function of n arguments.
In the above example, for instance:
f (g x) (h y) (i z)
Suppose you want (h y) to be strictly evaluated. I argue that some
variation on this:
f (g x) $! (h y) $ (i z)
even with the parentheses is far more readable than the current
alternatives.
While it makes sense that ($!) should have the same associativity as
($), I can't for the life of me figure out why ($) is right-associative.
There's probably a terribly good reason. Does anyone know what it is?
Cheers,
Andrew Bromage
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