Significant whitespace

[Mark Wilson]

On Thursday, October 9, 2003, at 11:19 PM, Greg Ewing (using 
news.cis.dfn.de) wrote:

> Marcin 'Qrczak' Kowalczyk wrote:
>> Having failed with significant indents, I tried to use significant 
>> line
>> breaks in next incarnations of my language, which looked like a good
>> compromise. ... I had
>> troubles with designing a good syntax for some constructs, mainly
>> if-then-else, being constrained to syntaxes which can be nicely split
>> into lines.
>
> While pondering that sort of problem one day I devised a scheme for
> handling syntaxes where some line breaks are required and others are
> optional.
>
> The idea is that instead of the scanner returning line breaks as
> tokens of their own, there is a flag associated with the current
> token that indicates whether it is followed by a line break.
>
> When parsing something that doesn't care whether it has line
> breaks in it or not, the parser ignores this flag. But when it
> gets to a point where a line break could be significant, it takes
> notice of it.
>
> For instance, when parsing
>
>    a = b +
>       c
>
> the parser would ignore the line break flag while looking at
> the '+' because it knows there must be more of the expression
> coming. But when it gets to the 'c', it would check the line
> break flag, find it set, and conclude that the expression is
> finished.
>
> This ought to allow extra line breaks to be placed wherever
> they don't lead to any ambiguity.
>
> I haven't had a chance to try this out, however, so there
> may be some problems that I haven't anticipated!

This is what Ruby does now.

Regards,

Mark Wilson