threads / discuss / 4230

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

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

## tl;dr

2 messages between May 21, 2006 and May 21, 2006.

replies: 1people: 1as markdown or json

Jakub Narebski· May 21, 2006, 08:06 UTC · lore

Shawn Pearce wrote:

Show 9 quoted lines

> 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))))

Rather

    (peel-onion 'tree (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]?

Interpreting said parse tree anch checking if it folds to correct object reference is the task of interpreter, not parser...

[*1*] if I understand currectly that <commit-ish> mean direct sha1, shortened sha1, or ref (head or tag)? commit-ish is not in git glossary...

-- 
Jakub Narebski
Warsaw, Poland

Jakub Narebski· May 21, 2006, 10:13 UTC · re: Jakub Narebski · lore

Jakub Narebski wrote:

Show 19 quoted lines

> 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