Nasal Loops: Difference between revisions

for( preloop_initialization; # will be run prior to the first invocation of the loop, usually to initialize a loop counter

     condition_during_loop;  # will be run prior to each iteration, usually to check the loop counter  and cancel the loop if false

for (var i=0; i < 3; i = i+1) {

     # loop body

The differences are that there is no <tt>do{}while()</tt>; construct, and there is a foreach/forindex, which takes a local variable name as its first argument and a vector as its second:

foreach(elem; list1) { doSomething(elem); }  # NOTE: the delimiter is a SEMICOLON ;

</syntaxhighlight>

The hash/vector index expression (one that uses brackets) is an lvalue that can be assigned as well as inspected:

foreach(light; lights) { lightNodes[light] = propertyPath; }

</syntaxhighlight>

To walk through all elements of a hash, use a foreach loop on the keys of they hash. Then you call pull up the values of the hash using the key.  Example:

myhash = {first: 1000, second: 250, third: 25.2 };

foreach (var i; keys (myhash)) {

There is also a "forindex", which is like foreach except that it assigns the ''index'' of each element, instead of the value, to the loop variable.

forindex(i; list1) { doSomething(list1[i]); }

</syntaxhighlight>

Also, braceless blocks work for loops equally well:

var c = 0;

while( c < 5 )

For operations that should continue over a longer period, one needs a non-blocking solution. This is done by letting functions call themselves after a timed delay:  

var loop = func {

     print("this line appears once every two seconds");

The fewer code FlightGear has to execute, the better, so it is desirable to run loops only when they are needed. But how does one stop a loop? A once triggered timer function can't be revoked. But one can let the loop function check an outside variable and refuse calling itself, which makes the loop chain die off:

var running = 1;

var loop = func {

This can be solved by providing each loop chain with a ''loop identifier'' and letting the function end itself if the id doesn't match the global loop-id. Self-called loop functions need to inherit the chain id. So, every time the global loop id is increased, all loop chains die, and a new one can immediately be started.

  var loopid = 0;

  var loop = func(id) {