Loops/Wrong ranges: Difference between revisions

=={{header|Lua}}==

{{works with|Lua|5.0 - 5.4, and perhaps beyond, but not before}}

Lua >= 5.4 will not allow a zero increment, causes a runtime error (trapped below).

Lua 4.0 - 5.3 will allow a zero increment, causing either: no execution (start<stop) or infinite execution (start>=stop).

''(though Lua 4.0 is not supported in the code below for other reasons.)''

Lua <4.0 didn't have numeric for loops, so behaviour would depend on how an equivalent repeat/while loop was written.

<lang Lua>tests = {

{ -2, 2, 1, "Normal" },

{-2, 2, 0, "Zero increment" }, -- 5.4 error

{-2, 2, -1, "Increments away from stop value" },

{-2, 2, 10, "First increment is beyond stop value" },

{ 2, -2, 1, "Start more than stop: positive increment" },

{ 2, 2, 1, "Start equal stop: positive increment" },

{ 2, 2, -1, "Start equal stop: negative increment" },

{ 2, 2, 0, "Start equal stop: zero increment" }, -- 5.4 error

{ 0, 0, 0, "Start equal stop equal zero: zero increment" } -- 5.4 error

}

unpack = unpack or table.unpack -- polyfill 5.2 vs 5.3

for _,test in ipairs(tests) do

start,stop,incr,desc = unpack(test)

io.write(string.format("%-44s (%2d, %2d, %2d) : ",desc,start,stop,incr))

local sta,err = pcall(function()

local n = 0

for i = start,stop,incr do

io.write(string.format("%2d, ", i))

n=n+1 if n>=10 then io.write("...") break end

end

io.write("\n")

end)

if err then io.write("RUNTIME ERROR!\n") end

end</lang>

{{out}}

Using 5.3:

<pre>Normal (-2, 2, 1) : -2, -1, 0, 1, 2,

Zero increment (-2, 2, 0) :

Increments away from stop value (-2, 2, -1) :

First increment is beyond stop value (-2, 2, 10) : -2,

Start more than stop: positive increment ( 2, -2, 1) :

Start equal stop: positive increment ( 2, 2, 1) : 2,

Start equal stop: negative increment ( 2, 2, -1) : 2,

Start equal stop: zero increment ( 2, 2, 0) : 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, ...

Start equal stop equal zero: zero increment ( 0, 0, 0) : 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...</pre>

Using 5.4:

<pre>Normal (-2, 2, 1) : -2, -1, 0, 1, 2,

Zero increment (-2, 2, 0) : RUNTIME ERROR!

Increments away from stop value (-2, 2, -1) :

First increment is beyond stop value (-2, 2, 10) : -2,

Start more than stop: positive increment ( 2, -2, 1) :

Start equal stop: positive increment ( 2, 2, 1) : 2,

Start equal stop: negative increment ( 2, 2, -1) : 2,

Start equal stop: zero increment ( 2, 2, 0) : RUNTIME ERROR!

Start equal stop equal zero: zero increment ( 0, 0, 0) : RUNTIME ERROR!</pre>