2.4.5 • 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 shown here are 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 explist 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.
EVERYTHING
For Statement

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