Context: Since Lua strings are immutable (and interned, like Erlang atoms, Lisp symbols, etc.), tables can be used as string buffers, and concatenation to large

Context: Since Lua strings are immutable (and interned, like Erlang atoms, Lisp symbols, etc.), tables can be used as string buffers, and concatenation to large strings can be done in one step via table.concat. Appending to a string in a loop is slow, but that's true of any language with immutable strings. $ time lua -e 't={};for i=1,100000 do table.insert(t,"-");end; s=table.concat(t,"")' 0m0.05s real 0m0.05s user 0m0.01s system 0m0.05s real 0m0.05s user 0m0.00s system 0m0.05s real 0m0.04s user 0m0.02s system (Times on OpenBSD/amd64 4.7, Lua 5.1.4.) table.insert checks the table's length on each iteration, which dominates the string-handling time - len is O(lg n). If you just use the loop index (or otherwise cache it), it cuts the time in half: $ time lua -e 't={};for i=1,100000 do t[i] = "-"; end; s=table.concat(t,"")' 0m0.02s real 0m0.02s user 0m0.00s system 0m0.02s real 0m0.02s user 0m0.01s system 0m0.02s real 0m0.03s user 0m0.00s system Changing to i=1,1000000 gave me an avg. of 0.54s and 0.22s respectively. LuaJIT is probably also considerably better. (You could also just do t = string.rep('-', 100000), but that's not the point of your benchmark.)