Re: How to fontify region according to mode

[Dan Davison <davison@stats.ox.ac.uk>]

Lennart Borgman <lennart.borgman@gmail.com> writes:

> On Sat, Aug 14, 2010 at 8:08 PM, Dan Davison <davison@stats.ox.ac.uk> wrote:
>> Lennart Borgman <lennart.borgman@gmail.com> writes:
>>
>>> On Sat, Aug 14, 2010 at 7:14 PM, Dan Davison <davison@stats.ox.ac.uk> wrote:
>>>> I want to write a function to fontify a region according to a certain
>>>> mode, and I tried the following tactic (see function below):
>>>>
>>>> - get the value of `font-lock-defaults' from a buffer in the target mode
>>>>  and bind it inside a let
>>>> - bind a bunch of other font-lock variable names to stop them being
>>>>  overwritten
>>>> - call `font-lock-set-defaults'
>>>> - call `font-lock-fontify-region'
>>>>
>>>> It didn't seem to work. Could someone suggest how to alter this so that
>>>> it works, or is this approach fundamentally flawed?
>>>>
>>>> (defun dan/font-lock-fontify-region (mode start end)
>>>>  (let ((font-lock-defaults
>>>>         (with-temp-buffer
>>>>           (funcall mode)
>>>>           font-lock-defaults))
>>>>        font-lock-keywords
>>>>        font-lock-keywords-only
>>>>        font-lock-keywords-case-fold-search
>>>>        font-lock-syntax-table
>>>>        font-lock-beginning-of-syntax-function)
>>>>    (font-lock-set-defaults)
>>>>    (font-lock-fontify-region start end)))
>>>>
>>>>
>>>> I want the rest of the buffer to remain unaltered and, for now, I'm not
>>>> looking for a solution involving mumamo/multi-mode etc.
>>>
>>>
>>> If you want to see how it works then look in mumamo.el. I think you
>>> will find the answers to your questions there. (But why do you want to
>>> reinvent the wheel? What is the purpose?)
>>
>> Hi Lennart,
>>
>> I was looking at mumamo.el earlier today, but it is 9,101 lines long, so
>> I would definitely appreciate some guidance. Note that I don't want
>> different regions to be subject to different major modes; I only want to
>> change the text properties in a region. That was why I was not using
>> mumamo and was attempting the simple approach above. I would certainly
>> consider mumamo if I wanted multiple major modes.
>>
>> Dan
>
>
> Hi Dan,
>
> I am afraid that what you want actually involves the same problem as
> using multiple major modes. Why don't you think so?

Hi Lennart,

OK, I see. It looks like I was being naive and thinking it was simpler
than it really is. Seeing as you have worked extensively on this, and as
I have wasted a little bit of time on it, would you mind explaining to
me where my above approach encounters problems?  I.e., inside a let
binding,

1. bind `font-lock-defaults' to the appropriate value
2. bind to nil all the other font-lock related variables that
   `font-lock-set-defaults' will change
3. call `font-lock-set-defaults'
4. call `font-lock-fontify-region'

Thanks,

Dan