Re: [idea] Converting sha1 evaluator into parser/interpreter

Jakub Narebski wrote:

> Shawn Pearce wrote:
> 
>> There was just a short conversation on #git about converting
>> the sha1 expression evaluator into a split parser/interpreter
>> model.  The idea here would be to convert an expression such as
>> 
>>   HEAD@{yesterday}~3^{tree}
>> 
>> into a an expression tree such as (in LISP style):
>> 
>>   (peel-onion (walk-back 3 (date-spec yesterday (ref HEAD))))
>>
>> with such a tree it is relatively easy to evaluate the expression,
>> but its also easy to determine if a ref name is valid.  Just pass
>> it through the parser and see if you get back anything more complex
>> then '(ref <input>)'.
> 
> Didn't you meant to see if we get correct tree (not a forest), 
> and if the root of said tree is '(ref <commit-ish>)' [1]?

I'm sorry. Of course branch names (ref names) should be limited to the ones
that doesn't make problems for the parser, i.e. they should parse to single
element parse tree:

   <input> ---parses to---> (ref <input>)

and doesn't give problems for other parsers (e.g.commit list parser
including '^A B' and 'A..B'; remotes branch mapping parser 'srcref:destref'
and '+srcref:destref') and shell (e.g. globbing).


P.S. Hmmm... is '--' branch name (heads/--) possible?
P.P.S. Would branch name which include '!' and/or '$' cause trouble?

-- 
Jakub Narebski
Warsaw, Poland

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