[boost] Re: Review Request: FC++

From: David Abrahams (dave_at_[hidden])
Date: 2003-10-08 16:45:51

"Powell, Gary" <powellg_at_[hidden]> writes:

> Dave Abrahams wrote:
> -----------------------------------------------------------------
> a. Is there a *reason* that square brackets have to be used for
>    postfix function args in lambdas?
>
> b. It  seems like 
>
>    lambda(X)[ let[ Y == X %plus% 3,
>                    F == minus[2] 
>               ],
>               F[Y]
>             ]
>
>    would be a little sweeter, syntactically speaking.
> -----------------------------------------------------------------
>
> isn't there a parsing issue here? Where the "," impiles two arguments
> to the Lambda(X)[] function call

Uhm, operator[] can only take a single argument in C++

> when you really want one fc++Lambda object from binding the ","
> first. which makes you write:
>
>    lambda(X)[ (
>               let[ Y == X %plus% 3,
>                    F == minus[2] 
>               ],
>               F[Y]
>               )
>             ]

I don't see how that changes the parsing.

IIUC Foo[expr1, expr2] is always parsed as

  Foo.operator[](operator,(expr1, expr2))

which is equivalent to 

  Foo.operator[]((operator,(expr1, expr2)))

and

  Foo[(expr1, expr2)]

> which for me is worse. As the let has to generate an object that is
> unique enough to be recongnized to bind to the F[Y] and generate
> useful compiler errors otherwise.

Well, that part is true, and I'll admit I haven't thought about the
possible implementation problems at that level.

> Note: my opinion is really biased as Jaakko and I came up with a
> different syntax.

I guess the number of reinvented wheels we have in overlapping
domains is starting to worry me a bit here, though I'm not ready to
object yet.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com