On 2/20/13, David A. Wheeler <dwhee...@dwheeler.com> wrote:
> Beni Cherniavsky-Paskin:
>> > This behaves surprisingly:
>> >
>> > $
>> > ! a b
>> > ! c d
>> > ==>
>> > ((a b (c d)))
>> >
>> > it seems $ consumes the following newline, resulting in same parsing as
>> > if I
>> > wrote
>> >
>> > $ a b
>> > c d
>> >
>> > Is this deliberate?
>
> Alan Manuel Gloria
>> No (at least not by me; check David's answer, but I suspect he didn't
>> implement it deliberately that way).
>
> Alan's right, that's unintentional in the Scheme implementation.
>
> The BNF does not permit this construct at all, so the ANTLR implementation
> will give an error in this case.
>
> The relevant production is it_expr, which permits only:
> | SUBLIST hspace* is_i=it_expr {$v=list($is_i.v);} /* "$" first on line
> */
> That is, "$", after any hspaces, MUST be followed with an it_expr, and
> CANNOT
> be followed currently by ";" or an end-of-line marker.
>
>
>> Every example we have has some
>> other datum after the "$", I never said anything about $-at-eol ever
>> since I first proposed SUBLIST on the mailinglist, and so on, so you
>> might legitimately say that this is "unspecified".
>>
>> > Since "a b" is on a child line, I'd it to parse in the same manner as "c
>> > d",
>> > resulting in ((a b) (c d)).
>>
>> That seems reasonable, given your rules. One might say that:
>>
>> $
>> ! a b
>> ! c d
>> ==>
>> $ \\
>> ! a b
>> ! c d
>
> I'm okay with that, especially if it makes using the construct "more
> natural"
> and avoids turning a plausible use into an error.
>
> It's a trivial 1-line addition to the BNF. If we *don't* add that, then I
> clearly
> need to add an error-check to the Scheme implementation.
>
Hmmm....
$
! a b
! c d
INDENT ; stack: (0 ?)
INDENT a b ; stack: (0 ? 2)
SAME c d ; stack: (0 ? 2)
DEDENT DEDENT
\\
!\\
!!a b
!!c d
(
(
(a b)
(c d)))
==> (((a b) (c d))), not ((a b) (c d)) - note the extra () introduced
by $ compared to \\
--
However despite that, Beni's let example is correct:
let $
x $ compute 'x
y $ compute 'y
use x
let INDENT ; stack: (0 ?)
INDENT x INDENT compute 'x ; (0 ? 4 ?)
DEDENT ; stack (0 ? 4), indentation 4
y INDENT compute 'y ; (0 ? 4 ?)
DEDENT DEDENT ; stack (0 ?), indentation 2
use x ; stack (0 2)
DEDENT
let
!\\
!!x
!!!compute 'x
!!y
!!!compute 'y
!use x
>> > [I'm asking this because if it's 'fixed, my
>> > closing-SUBLIST-by-unmatched-dedent would allow:
>> >
>> > let $
>> > ! ! x $ compute 'x
>> > ! ! y $ compute 'y
>> > ! body...
>> > ]
>
> I have a *lot* of concerns with that particular construct.
>
> But we could certainly allow $-at-end-of-line regardless,
> on the grounds of consistency.
>
> So let's add $-at-EOL, unless someone objects soon.
>
> --- David A. Wheeler
>
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