As I posted earlier, I'm *really* uncomfortable with losing the ability to
auto-check the grammar. But I do understand the notion that extending SUBLIST,
especially to handle "let" and similar constructs, could be useful.
Beni Cherniavsky-Paskin:
>[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 counter-proposal, maybe I can call it "Beni-Lite" :-) ??? And I even
have a sample implementation that we can try out.
I've just posted to the "devel" branch a change to the ANTLR implementation
that permits closing SUBLIST by an unmatched DEDENT, but *only* if the "$" is
the last item on a line (and there's something before "$" other than indent
chars). This limited semantic ("Beni-lite"?) covers the primary use cases I've
seen, *AND* I've found a way to formulate it so that we can continue to use
ANTLR's grammar checking and run-time input checking.
To do this, I've tweaked the indent processor. After you dedent, if the dedent
doesn't match the parent indent, it then generates a RE_INDENT. This retains a
whole lot of error-checking, both of the BNF and of the input during
processing. This means that:
let $
! ! var1 value1
! body...
becomes:
let SUBLIST EOL
INDENT var1 value2 EOL
DEDENT RE_INDENT body...
It includes a few test cases, which show how it works:
let $
! ! var1 value1
! body...
; ==> (let ((var1 value1)) body...)
let $
! ! var1 value1
! ! var2 value2
! body...
; ==> (let ((var1 value1) (var2 value2)) body...)
let $
! ! var1 value1
! ! var2 value2
! ! var3 value3
! body1 param1
! body2 param2
; ==>
; (let ((var1 value1) (var2 value2) (var3 value3))
; (body1 param1) (body2 param2))
Even this backed-off version is complicated, but it's not MUCH more
complicated, and it does retain all the error-checking that I'm very loathe to
drop. It only works when "$" is at the end of the line... but that seems like
a reasonable limitation.
Comments?
I *especially* want to hear from Beni Cherniavsky-Paskin and Alan Manuel
Gloria, since both have expressed an interest in this kind of capability, but I
certainly want to hear from all. I want to make this final notation a good
balance between "simple" and "capable"... I worry that even this subset may be
a step too far.
--- David A. Wheeler
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