NETIO Lua Manual

Loops

Numeric for

local arr = {2,3,7,5}
for i=1,#arr do logf("%d",arr[i]) end

for initVar,limit,increment do

• number assignment initVar inits loop-local variable
• number limit loops until initVar reaches this value
• optional number increment after each loop initVar increment by this value (default 1)

Generic for

Most common example (the order of elements in pairs() is not guaranteed)

local tab = {one=1, two=2, three=3}
for key,val in pairs(tab) do logf("%s:%d",key,val) end

Generic for syntax

for var_1, ..., var_n in explist do block end

is equivalent to (Full explanation here.)

do
  local _f, _s, _var = explist
  while true do
    local var_1, ... , var_n = _f(_s, _var)
    _var = var_1
    if _var == nil then break end
    block
  end
end

Iterator closure that holds its state

function iter(a)
  local i = 0
  return function()
    i = i+1
    return a[i]
  end
end

local arr = {2,3,7,5}
for value in iter(arr) do
  logf("%d",value)
end

Stateless iterator (in this case returns variable list: key and value)

function iter(a,i)
  i = i+1
  if a[i] then return i,a[i] end
end

local arr = {2,3,7,5}
for k,v in iter,arr,0 do
  logf("%d:%d",k,v)
end

Same effect using ipairs() Lua function (without initial state)

for k,v in ipairs(arr) do
  logf("%d:%d",k,v)
end

Now return to the most common example above using pairs() Lua function and read about pairs() and ipairs() implementation here.