A lexical change (a breaking change, but trivial to fix)

[Mehrdad]

On Saturday, 7 July 2012 at 22:54:15 UTC, Timon Gehr wrote:
> On 07/08/2012 12:23 AM, Mehrdad wrote:
>
> 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;
> }

You kinda glossed over the crucial detail in parseNumber().  ;)

What happens if it sees   "2..3" ?

Then it /must/ have eaten the first period (it can't see the 
second period otherwise)... in which case now you have no idea 
that happened.

Of course, it's trivial to fix with an extra lookahead, but that 
would require using a forward range instead of an input range. 
(Which, again, is easy to do with an adapter -- what I ended up 
doing -- but the point is, it makes it harder to lex the code 
with just an input range.)