For Statement

The for statement has two forms: one numeric and one generic.

The numeric for loop repeats a block of code while a control variable runs through an arithmetic progression. It has the following syntax:

	stat ::= *for* Name `*=*` exp `*,*` exp [`*,*` exp] *do* block *end*

The block is repeated for name starting at the value of the first exp, until it passes the second exp by steps of the third exp. More precisely, a for statement like

     for v = _e1_, _e2_, _e3_ do _block_ end

is equivalent to the code:

     do
       local _var_, _limit_, _step_ = tonumber(_e1_), tonumber(_e2_), tonumber(_e3_)
       if not (_var_ and _limit_ and _step_) then error() end
       while (_step_ > 0 and _var_ <= _limit_) or (_step_ <= 0 and _var_ >= _limit_) do
         local v = _var_
         _block_
         _var_ = _var_ + _step_
       end
     end

Note the following:

All three control expressions are evaluated only once, before the loop starts. They must all result in numbers.
_var_, _limit_, and _step_ are invisible variables. The names are here for explanatory purposes only.
If the third expression (the step) is absent, then a step of 1 is used.
You can use break to exit a for loop.
The loop variable v is local to the loop; you cannot use its value after the for ends or is broken. If you need this value, assign it to another variable before breaking or exiting the loop.

The generic for statement works over functions, called iterators. On each iteration, the iterator function is called to produce a new value, stopping when this new value is nil. The generic for loop has the following syntax:

	stat ::= *for* namelist *in* explist1 *do* block *end*
	namelist ::= Name {`*,*` Name}

A for statement like

     for _var_1_, ..., _var_n_ in _explist_ do _block_ end

is equivalent to the code:

     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

Note the following:

_explist_ is evaluated only once. Its results are an iterator function, a state, and an initial value for the first iterator variable.
_f_, _s_, and _var_ are invisible variables. The names are here for explanatory purposes only.
You can use break to exit a for loop.
The loop variables _var_i_ are local to the loop; you cannot use their values after the for ends. If you need these values, then assign them to other variables before breaking or exiting the loop.