Subject: Re: [PATCH 0/3] Generalized "string function" syntax

From: René Scharfe <[email-masked]>
Date: Sun, 18 Oct 2009 10:24:50 +0200

Junio C Hamano schrieb:
> René Scharfe <[email-masked]> writes:
> 
>> Junio C Hamano schrieb:
>>> I mentioned an idea to enhance the pretty=format language with a
>>> string function syntax that people can extend by adding new functions
>>> in one of the "What's cooking" messages earlier.  The general syntax
>>> would be like
>>>
>>> %[function(args...)any string here%]
>>>
>>> where "any string here" part would have the usual pretty=format
>>> strings. E.g.  git show -s --format='%{w(72,8,4)%s%+b%]' should give
>>> you a line wrapped commit log message if w(width,in1,in2) is such a
>>> function.
>> I pondered line wrapping with format strings briefly a long time ago, and
>> I always considered it to be more similar to a colour, i.e. a state that
>> one can change and that is applied to all following text until the next
>> state change.  (Except that it's always reset at the end of the format
>> string.)  The example above would then turn into '%w(72,8,4)%s%+b'.
> 
> As a syntax to express "wrapping" behaviour alone, I think this is much
> simpler and more superiour.  I guess with this if you want to wrap
> something to 72 columns and then wrap something else to 66 columns, you
> would write '%w(72,8,4)something%w(66,8,4)something else', right?

That's right.

> I used %] only for two reasons.
> 
>  - Without an explicit "here it ends", I couldn't come up with a good way
>    to express '%[w(72,8,4)something%]something else'.  IOW, how I can say
>    "wrap something to 72 columns and then place something else without any
>    wrapping"?

My patch makes '%w()' reset the wrapping parameters to their defaults.

>  - When we need to support more than one string function like this, it is
>    unclear what '%f()one string%g()another one' in your syntax means.
>    Does it mean '%[f()one string%]%[g()another one%]' (i.e. concatenate
>    the result of applying string function f to 'one string' and the result
>    of applying string function g to 'another one')?  Or does it mean
>    '%[f()one string%[g()another one%]%]' (apply 'f' to concatenation of
>    'one string' and the result of applying 'g' to 'another one')?

I was going to say that we already have something like that with %C, and
that the natural way (to me) is to apply them both, independently.  Case
modification functions (upper, lower, capitalized) could be treated the
same way -- as state changes (like pressing caps lock when typing text).

Which other text functions are we going to add which would break this
model?  The only thing I can think of right now is nesting such
functions themselves, e.g. when indenting a list in an indented
sub-paragraph in an indented paragraph.  Useful?

But then something else hit me: the line wrap function needs to consider
colour codes as having a length of zero.  Ugh.

René