Re: example 7.17 in YAML 1.2 spec 2009-07-21

Oren,

> On Wed, 2009-09-30 at 22:05 +0900, Osamu TAKEUCHI wrote:
>> Imagine an input:
>>
>> {::::}
>>
>> With the new rule set, I at first expected the next.
>>
>> !!map
>>   ? !!str ":::"
>>   : !!null
>>
>> But actually, this input became invalid under the new rule set.
> 
> I must say I _like_ this being an error.
> The idea is that ':' is treated as part of the plain character if it is
> followed by something that makes it _clear_ it is not a key:value
> separator.
> Obviously in this case, there's no such indication.
> IMO _however_ you interpret it, some people will be confused.
> 
> Given out #1 goal is readability, I think treating this as an error is a
> _good thing_.

Your definition does not seem to increase readability.
Let me show some examples.

Your opinion:

{a}         =>  { "a" : null }
{a:}        =>  { "a" : null }
{a: b}      =>  { "a" : "b" }
{a::}       =>  error
{a:: b}     =>  error
{a::a}      =>  { "a::a" : null }
{a::a:}     =>  { "a::a" : null }
{a::a: b}   =>  { "a::a" : "b" }
{a::a::}    =>  error
{a::a:: b}  =>  error

My opinion:

{a}         =>  { "a" : null }
{a:}        =>  { "a" : null }
{a: b}      =>  { "a" : "b" }
{a::}       =>  { "a:" : null }
{a:: b}     =>  { "a:" : "b" }
{a::a}      =>  { "a::a" : null }
{a::a:}     =>  { "a::a" : null }
{a::a: b}   =>  { "a::a" : "b" }
{a::a::}    =>  { "a::a:" : null }
{a::a:: b}  =>  { "a::a:" : "b" }

The idea is that ':' is treated as part of the plain text
unless it is followed by a delimiter in the context, which
includes a space and a line break.

My definition will be more understandable because we do not 
have to think what is "something that makes it _clear_ it is 
not a key:value separator." In addition, we have to look ahead
only one character. Your rule requires to look ahead many 
characters.

{a:::::::::::b}   =>   { "a:::::::::::b" : null }
{a::::::::::::}   =>   error

Note that, in this case, we have to look ahead more than ten 
characters in order to determine whether or not the first ":" 
is ns-plain-char.


>> The answer seems to be the next.
>> > 
>> > ( ":" /* Followed by ( ns-plain-safe(c) | "#" | ":" ) */ )
> 
> There's no need to add '#' since it will be caught by ns-plain-char(c)
> since it is not preceded by a space.

There's a need to add '#' since it will not be caught by ns-plain-safe(c)
even though it is not preceded by a space nor line break. ;)

Best,
Osamu TAKEUCHI

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