On 7/12/14, aparsloe <[log in to unmask]> wrote: > On 12/07/2014 3:13 p.m., Bruno Le Floch wrote: >> Can you expand on that one exception? I don't see what it is. > I found myself on occasion wanting to substitute a number in expressions > where pi is followed by other terms. For instance the fine structure > constant is 2pi e^2/hc (where e is the electronic charge in this case) > but direct substitution of values for e etc. simply provokes an > "Undefined control sequence" message. Since numbers are not (as far as I > understand) elements of control sequences, this felt like an unnecessary > limitation. (But I'm not familiar with the underlying constraints. Hence > the "perhaps".) Not sure what you mean here. Doing \fp_show:n { 2pi e^2/hc } gives two errors: \LaTeX3 error: Unknown fp word pie. \LaTeX3 error: Unknown fp word hc. Doing \fp_const:Nn \c_aparsloe_e_fp { 1.60217657e-19 } \fp_const:Nn \c_aparsloe_h_fp { 6.62606957e-34 } \fp_const:Nn \c_aparsloe_c_fp { 299 792 458 } \fp_show:n { 2pi \c_aparsloe_e_fp ^2 / ( \c_aparsloe_h_fp \c_aparsloe_c_fp ) } works (except that since I've used values in SI units for e, h, c, the formula for the fine structure constant is missing a factor of sqrt(4pi*epsilon0)). > As I've tried to indicate, I've come to realise that what matters is > clarity in what the rules are and the rigour of their application. My > concern was with people who might, at present, use a (clunky?) package > like calc, or fp, coming across l3fp, being seduced (like me) and coming > a cropper (as I did). The proposed change will certainly reduce that > possibility. I'm not sure what change you propose (besides the precedence of juxtaposition, which will change soonish), and it will be helpful if you clarify. Regards, Bruno