On Fri, 4 Apr 2008, Peter Münster wrote:

> On Fri, Apr 04 2008, Taco Hoekwater wrote:
>>
>>    % engine=luatex
>>
>>    \startluacode
>>    function add_ties (line) return line:gsub(' ','~') end
>>    \stopluacode
>>
>>    \def\startfiltered
>>      {\ctxlua {callback.register('process_input_buffer', add_ties)}}
>>    \def\stopfiltered
>>      {\ctxlua {callback.register('process_input_buffer', nil)}}
>>
>>    \starttext
>>    \startfiltered
>>    Thus, I came to the conclusion that the designer of a new system
>>    must not only be the implementer and first large||scale user; the
>>    designer should also write the first user manual.
>>    \stopfiltered
>>    \stoptext
>>
>> Notice how it breaks only at hyphens? If you think that is because
>> those are the only valid breakpoints, you are actually slightly wrong:
>> there are still 'normal' spaces between 'system' and 'must' and between
>> 'the' and 'designer' (because EOL is converted to a space *after*
>> reading in the line buffer).
>>
>> The lua function is _much_ too simple. It will happily convert '\ '
>> into '\~', $a = 2~$ into $a~=~2~$, and "\TEX is" into "\TEX~is".
>
> Hello,
>
> Perhaps this one could be already useable for the OP:
>
> function add_ties(line)
> 	line = line:gsub('( %a) ', '%1~')
> 	line = line:gsub('^(%a) ', '%1~')
> 	line = line:gsub('( %a)$', '%1~%%')
> 	return line
> end
>
> Not working: $a = b + c$.

How about substituting with a macro \nonbreakbablespace (instead of ~) and 
redefining \nonbreakablespace to \relax using \everymathematics or 
\mathortext?

Aditya