On 07/08/2012 12:23 AM, Mehrdad wrote:
On Saturday, 7 July 2012 at 22:00:43 UTC, H. S. Teoh wrote:
On Sat, Jul 07, 2012 at 11:39:59PM +0200, Mehrdad wrote:
This might sound silly, but how about if D stopped allowing 0..2
as a range, and instead just said "invalid floating-point number"?
[...]
I like writing 0..2 as a range. It's especially nice in array slice
notation, where you _want_ to have it as concise as possible.
Hmm... true..
OTOH, having implemented a D lexer before (just for practice, not
production quality), I do see how ambiguities with floating-point
numbers can cause a lot of code convolutions.
Yeah that's exactly what happened to me lol.
(Mainly the problem I ran into was that I was REALLY trying to avoid
extra lookaheads if possible, since I was sticking to the range
interface of front/popFront, and trying not to consume more than I can
handle... and this was the edge case that broke it.)
You could go like this:
switch(input.front) {
case '0'..'9':
bool consumedtrailingdot;
output.put(parseNumber(input, consumedtrailingdot));
if(!consumedtrailingdot) continue;
if(input.front != '.') {
output.put(Token("."));
continue;
}
input.popFront();
if(input.front != '.') {
output.put(Token(".."));
continue;
}
output.put(Token("..."));
continue;
}
But I'm gonna have to say no to this one; *I* think a better solution
would be to prohibit things like 0. or 1. in a float literal. Either
follow it with a digit, or don't write the dot. This will also save us
a lot of pain in the UFCS department, where 4.sqrt is currently a pain
to lex. Once this is done, 0..2 is no longer ambiguous, and any
respectable DFA lexer should be able to handle it with ease.
Good idea, I like it too. How about just disallowing trailing decimal
points then?
+1.
