From: Daniel Sheppard <daniels@...>
Date: 2007-02-20T14:13:13+09:00
Subject: Re: [YAML] To quote or not to quote (I think it's a bug)

 
> "Any "*_*" characters in the number are ignored, allowing a readable
> representation of large values."
> 
> So clearly they're allowed, in 1.2_3 the underscore is simply 
> ignored and
> the parser should undestand 1.23. If I fancy to write my own 
> YAML by hand
> and make it easily readable (which is kind of the original 
> purpose) I could
> write 100_000_000.03 which would be a nice looking float. Hence the
> ambiguity with "1.2_3".

But the specification is not just in english, it's also in regex form:

 [-+]?([0-9][0-9_]*)?\.[0-9.]*([eE][-+][0-9]+)? (base 10)
|[-+]?[0-9][0-9_]*(:[0-5]?[0-9])+\.[0-9_]* (base 60)
|[-+]?\.(inf|Inf|INF) # (infinity)
|\.(nan|NaN|NAN) # (not a number)

For a base 10 number, underscores are permitted only if they appear
BEFORE the decimal point, so for 1.2_3 there is no ambiguity.

Dan.