On Wednesday 23 April 2008, Bulat Ziganshin wrote:
> Hello Dan,
>
> Wednesday, April 23, 2008, 1:42:20 PM, you wrote:
> > This wouldn't work, you'd have to rewrite it as:
> >
> > withSomeResource foo .
> > withSomeOtherThing bar .
> > yetAnotherBlockStructured thing $ ...
>
> it is very inconvenient - we should use either . or $ depending on
> that it's last block or not. imagine all the changes when editing the
> code
Well, that may be inconvenient, but I don't know how much such block
structured code is actually a composition of such functions. Off the top of
my head, I'd expect most to involve lambdas or dos:
forM l $ \e -> ...
State $ \s -> ... (see also Reader, Cont, ...)
runST $ do ... (or 'flip runM arg' for most monads, I suppose)
callCC $ \k -> ... (shift)
forever $ do ...
withResource $ \r -> ...
local f $ do ...
Which still work with the flipped associativity. The one oddity I noticed
looking at random code of mine is reset in Cont(T), which might currently be
used like:
reset $ forM l $ \e -> ...
for inverting loops. It would have to become:
reset . forM l $ \e -> ...
Which might be a little weird (of course, in CC-delcont, that's
reset $ \p -> forM l $ \e -> ...
so it's moot there, but I suppose this affects all the functions that rely
on 'do' to use repeated ($)s).
My code may well be abnormal, though (certainly, my infatuation with
continuations probably is :)).
When I do have composition pipelines that don't fit on one line (like the
initial example), I think I tend to write them like this:
pipe = foo
. bar
. baz
. quux
$ quuux
Which lets you slip new things in pretty naturally, I think.
There may be a lot of code out there that that all doesn't work for, though. I
don't know.
-- Dan
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