On 12/07/2014 4:22 a.m., Bruno Le Floch wrote
>>> In l3fp, I pushed the idea to its extreme, allowing juxtaposition for
>>> things other than units, and I kept the precedence as being the
>>> tightest possible.
>>>
>>> As Lars rightfully says it's "consistent, but not necessarily
>>> intuitive".  Andrew has given several cases where my choice leads to a
>>> terrible behaviour for l3fp, and there is basically no case where the
>>> current behaviour is better (well, there was one abusive one: with
>>> this rule, exp.5ln(...) computes the square root, but now that is not
>>> needed).
>> Actually, I've found this "abuse" quite a handy device, and despite the
>> introduction of the sqrt function to l3fp, for n-th roots, exp(1/n)ln
>> has a certain convenience.
> Well, that won't work once we change the precedence of juxtaposition
> to be the same as normal multiplication.  But IIRC, we added (perhaps
> in l3candidates?  I'll check) a way for users to define their own fp
> functions.  This is still experimental.  Looking at it, it seems we
> don't document \fp_function:Nw and \fp_new_function:Npn anywhere.
>
> Regards,
> Bruno
A previous version of interface3.pdf included some documentation of 
\fp_new_function:Npn and \fp_function:Nw -- in the l3candidates section. 
But when I check I see that It's missing from the latest version. On the 
basis of this earlier documentation I've used \fp_new_function:Npn for 
some simple-minded definitions of the hyperbolic functions and their 
inverses.

Andrew