On 11/16/2016 03:28 PM, Stephan Herrmann wrote:
On 11/17/2016 12:10 AM, Alex Buckley wrote:
On 11/16/2016 3:03 PM, Stephan Herrmann wrote:
On 11/16/2016 11:57 PM, Alex Buckley wrote:
On 11/16/2016 2:26 PM, Stephan Herrmann wrote:
And we may safely assume regularity of the grammar, i.e.,
the above approach will never lead to ambiguities, right?
Fictitious counter example
ModuleDeclaration:
module open Identifier ModuleBody;
module Identifier ModuleBody;
With this the second token could be keyword or identifier, and we're
stuck, aren't we?
May we assume that the grammar will not be extended in such ambiguous
ways?
There is already a production like this:
ModuleStatement:
requires transitive ModuleName ;
requires ModuleName ;
Outch!!
So when you read "requires transitive" which rule are you parsing
against?
When do you decide whether transitive is a keyword or an identifier?
I guess we have to wait until we matched the full rule.
That requires backtracking, or what am I missing?
Yes, you need to lookahead to a ;
Alex
So everything points at ';' to the rescue.
Unfortunately, while a user types a line of text, this essential
character will be missing until the very end, so tool support
for incomplete lines will not be great.
Not much we can do, I guess.
OK, thanks to you both, I believe I understand the intention.
I guess I made my point that I see tremendous difficulties
in providing good tool support, and that I'm not convinced
that the current definition matches to the intended solution.
I mentioned that all this could probably be avoided by using
an escape mechanism.
That said I will stop harping on these points,
Stephan
It is not quite as bad as that.
An identifier-that-might-be-a-keyword is definitely a restricted keyword
if it is followed by another identifier (including an
identifier-that-might-be-a-keyword) or static.
An identifier-that-might-be-a-keyword is definitely an identifier if it
is followed by a '.' or ';'.
So in the following horrible cases:
requires transitive transitive;
^ at this point you know the first
transitive was a restricted keyword and the second was an identifier
requires transitive transitive.transitive.transitive;
^ at this point you know the first
transitive was a restricted keyword, and that the second and any
subsequent instances are identifiers.
requires transitive static a.b.c.d.e.f.g.h.i.j;
^ at this point you know transitive was a
restricted keyword
In other words, you don't need unbounded lookahead.
-- Jon
