if filehandle ~= nil then
return filehandle
end
return false

This has been working okay, but I think

if filehandle ~= nil then
return filehandle, true
else
return nil, false
end

will more directly say what I mean. I need to read a little more to figure out which is more "idiomatic" for the language. (Or maybe ask @amic, who has used the language more than I have.)

#Lua