sugestions

[denisdemais]

first, congratulations for the project! very nice and usefully.

i.
if a expression is nil return (nil)

ii.
maybe uses $ prefix like php ${expression}

iii.
f()
accepts -> string f(" sum 1+1 = {1+1}");
accepts -> table f( { {"sum 1+1 = {1+1}, {"div 2/1 = {2/1}"}, ... } )