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

[Jakub Narebski <jnareb@gmail.com>]

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))))

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