Meta commands

[jens55]

Please forgive the stupid question but why is the following section in a macro causing an infinite loop ?

while true
  if iterations < 10
    m118 s"hello world"
    g4 s2
    continue
	
abort

[alankilian]

@jens55 You want to rewrite the logic of that code using a 'break' statement instead of a 'continue' statement.

'continue' causes the loop to go back to the top of the loop.
'break' causes the loop to be exited.

Maybe something like this? (UNTESTED)

while true
  m118 s"hello world"
  g4 s2
  if iterations > 9
    break

abort

From HERE:

A loop may contain one or more break statements, which would normally be inside if-constructs:

while <boolean-expression>
  ...
  if <boolean-expression>
    break
  ...

The break statement transfers control to the line following the end of the loop body.

A loop may also contain one or more continue statements, which would normally be inside if-constructs:

while <boolean-expression>
  ...
  if <boolean-expression>
    continue
  ...

The continue statement increments the iteration counter and transfers control back to the start of the loop, ready to evaluate the while-condition again.

[jens55]

Thanks for that but I still don't quite understand. From what I understand (yeah, very little), the 'continue' statement does go back to the top like you said but the block that has the 'continue' statement is in the loop of 'if iteration < 10.' So in my thinking, if iterations gets to 10, that 'if' block fails and the next executed statement should be 'abort' .... ????

[DanS79]

@jens55

It's just a guess, but since no commands are being run when the if statement fails interations might not get incremented (maybe a bug).

As a developer I'm not sure i like the concept of an iterations variable.

the documentation says this about it.
iterations - The number of completed iterations of the innermost loop

If you have nested looping structures it could get difficult to follow the code.

if i have all the syntax correct, something like this is more standard in the software development world.

var cnt = 0
while cnt < 10
    set var.cnt = cnt + 1
    m118 s"hello world"
    g4 s2

[alankilian]

@jens55 said in Meta commands:

Thanks for that but I still don't quite understand. From what I understand (yeah, very little), the 'continue' statement does go back to the top like you said but the block that has the 'continue' statement is in the loop of 'if iteration < 10.' So in my thinking, if iterations gets to 10, that 'if' block fails and the next executed statement should be 'abort' .... ????

You can take that 'continue' statement out completely and see that the macro runs just the same.

Every time the interpreter gets to the end of the loop it will jump back to the top of the loop.

So when the 'if' statement is not true, the interpreter does go to the next 'statement'. If there are no more statements in the loop, so it goes back to the top.

This might be a better way to do the loop and make it more understandable to you.

while iterations < 10
    m118 s"hello world"
    g4 s2

Or this might make it even MORE clear (I tested this one!)

m118 s"Starting the loop"
while iterations < 10
      m118 s"hello world"
      g4 s2
m118 s"Done with the loop"

8/12/2021, 2:27:26 PM 	Done with the loop
8/12/2021, 2:27:24 PM 	hello world
8/12/2021, 2:27:22 PM 	hello world
8/12/2021, 2:27:20 PM 	hello world
8/12/2021, 2:27:18 PM 	hello world
8/12/2021, 2:27:16 PM 	hello world
8/12/2021, 2:27:14 PM 	hello world
8/12/2021, 2:27:12 PM 	hello world
8/12/2021, 2:27:10 PM 	hello world
8/12/2021, 2:27:08 PM 	hello world
8/12/2021, 2:27:06 PM 	M98 P"0:/macros/000_test"
Starting the loop
hello world

[jens55]

@dans79, agreed, that is the way I am used to program a loop and yes, nested loops will be a nightmare.

[alankilian]

@jens55 said in Meta commands:

nested loops will be a nightmare.

Why?

Each loop gets its own iterator (which is what iterators ARE) so everything works out.

m118 s"Starting the loop"
while iterations < 3
      m118 s"hello world first"
      while iterations < 3
        m118 s"hello world second"
        while iterations < 3
          m118 s"hello world third"
m118 s"Done with the loop"

8/12/2021, 2:57:50 PM 	M98 P"0:/macros/000_test"
Starting the loop
hello world first
hello world second
hello world third
hello world third
hello world third
hello world second
hello world third
hello world third
hello world third
hello world second
hello world third
hello world third
hello world third
hello world first
hello world second
hello world third
hello world third
hello world third
hello world second
hello world third
hello world third
hello world third
hello world second
hello world third
hello world third
hello world third
hello world first
hello world second
hello world third
hello world third
hello world third
hello world second
hello world third
hello world third
hello world third
hello world second
hello world third
hello world third
hello world third
Done with the loop

[DanS79]

@alankilian said in Meta commands:

@jens55 said in Meta commands:

nested loops will be a nightmare.

Why?

Each loop gets its own iterator (which is what iterators ARE) so everything works out.

They are all called iterations.

If use want to use multiple of them to set a variable, the code would be very hard to read (assuming scoping even allows you to access all of them).

The following would be real confusing to follow if you replaced a, b, and c with iterations .

var x = 0
var a = 0
var b = 0
var c = 0
while a < 10
    set var.b = 0
    while b < 20
        set var.c = 0
        while c < 40
            set var.x = (a * b) - c
            set var.c = c + 1
         set var.b = b + 1
    set var.a = a + 1

[alankilian]

@dans79 Yeah, there are a thousand wrong ways to use a programming feature for every right way to use them.

[jens55]

I think we are drifting away from the part that I am having problems with which is why the particular construct I was using was having issues. Yes, there is a way to change things but WHY is it needed.

Here is a different way of going:

This works:

while iterations < 10
  m118 s{"hello world " ^ iterations}
  g4 s2
  continue

This gives:
Error: in file macro line 6 column 11: meta command: 'continue' was not inside a loop

while iterations < 10
  m118 s{"hello world " ^ iterations}
;  m118 s{"hello world " ^ iterations}
  g4 s2
  continue

The commented out line seems to dump the 'continue' statement outside of the loop and seems to me to be a bug in interpretation.

[alankilian]

@jens55 You don't need to add a 'continue' statement at the end of a loop.

[alankilian]

@jens55 said in Meta commands:

The commented out line seems to dump the 'continue' statement outside of the loop and seems to me to be a bug in interpretation.

You need to be very particular with the left-side whitespace to keep things working.

The interpreter is going to look at how many tab (or space)?) characters you have at the beginning of every line to know where the end of the loops are.

Your commented-out line starts with a semicolon in column one which tells the interperter that's the end of your while loop.

So, the 'continue' statement is not outside of the loop.

[jens55]

@alankilian, I realize that .... but what I am getting at is that something is fishy about how this is interpreted. While I don't need the 'continue', there should be nothing barring me from using it. It isn't inherently wrong.

[alankilian]

@jens55 That semicolon in column-1 causes the interpeter to end the while loop.

This works:

while iterations < 10
  m118 s{"hello world " ^ iterations}
  ;  m118 s{"hello world " ^ iterations}
  g4 s2
  continue

[jens55]

@alankilian, I will test that but the semicolon is there to comment out the line and should not cause this reaction.

[alankilian]

@jens55 This works to keep the whitespace:

while iterations < 10
  m118 s{"hello world " ^ iterations}
  ;  m118 s{"hello world " ^ iterations}
  g4 s2
  continue

[jens55]

@alankilian
@dc42
Ahhhh, I need the spaces before the comment .... ok but that s a bug in the interpreter

[alankilian]

This post is deleted!

[alankilian]

@jens55 said in Meta commands:

Ahhhh, I need the spaces before the comment .... ok but that s a bug in the interpreter

From the documentation:

The body ends just before the first line that is not indented.

So, it could be argued that the interpreter is working fine.

It's not up to me to decide.

I'm happy you're getting going on your project again.

And I learned some things from this discussion, so thank you for that also.

[jens55]

@dc42
Here is another example of strange behaviour:

while true
  if iterations < 10
    m118 s"hello world"
    g4 s2
    continue
break

This executes but leaves the printer in a 'busy' state
Without the 'break' command it does the same
If I move the 'break' command to the right by two spaces, everything finishes ok - it breaks out of the loop
Point is, there is no such thing as an 'endif' to clearly identify where the 'if' statement ends. IMHO there should be (optional maybe) an 'endif' for readability but in any case, the 'break' should break out of the loop no matter what.

Edit: On re-reading this, there is a flaw in my thinking here, and unless the 'break' is indented two spaces over, the 'while' loop has no exit. Interesting note here is that the iteration variable apparently isn't reset until after exiting the 'while' loop because it only prints 'hello world' for one 'if' loop.
That to me seems rather odd ....