Evaluating Mathematical Expressions using Lua

Question

In my previous question I was looking for a way of evaulating complex mathematical expressions in C, most of the suggestions required implementing some type of parser.

Answer 1

This is for Lua users that are looking for a Lua equivalent of "eval".

The magic word used to be loadstring but it is now, since Lua 5.2, an upgraded version of load.

 i=0
 f = load("i = i + 1") -- f is a function
 f() ; print(i) -- will produce 1
 f() ; print(i) -- will produce 2

Another example, that delivers a value :

f=load('return 2+3')
print(f()) -- print 5

As a quick-and-dirty way to do, you can consider the following equivalent of eval(s), where s is a string to evaluate :

load(s)()

As always, eval mechanisms should be avoided when possible since they are expensive and produce a code difficult to read. I personally use this mechanism with LuaTex/LuaLatex to make math operations in Latex.