Labels instead of line numbers

A line number in a jump is a choice, not an obligation. In the text form the target can be called by name

mediumYou need: Loops, Writing in the game

steptick 0

Set0

=

Operation1

=

+

Jump -> 12

if <

Set3

=

Stop4

@counter0number

countnullnull

readynullnull

set count 0
again:
op add count count 1
jump again lessThan count 5
set ready 1

The line again: is a label. It is not an instruction: it costs no line number, the processor does not execute it, and jump again leads to the line right after it.

The game itself parses such a program: labels are understood by its text parsing, not by some external editor. Copy the example into the “Edit code” window — it will work.

What it looks like

What	How it is written
declaring a label	a single word ending in a colon: again:
jumping to it	the name instead of a number: jump again always

The rules are simple:

• a label takes up the whole line; nothing else may be on it;
• the name can be anything, Cyrillic included;
• two labels with the same name are a parse error, not a silent substitution;
• a jump to a label that does not exist is an error too, and the game will say so.

Note

One program may hold up to 500 labels. That is a limit of the parsing, not of the logic: the jumps themselves are not going anywhere, the five hundred and first label simply will not be created.

What it is for

A line number is a fragile reference. Insert a line in the middle of a program and every jump below points to the wrong place — silently: the program keeps running, just incorrectly.

A label is tied to a place, not to a number. And it reads: jump checkStock says what is meant, while jump 17 says only which line.

Silent failure

The block editor has no labels at all. A program with labels opened as text in the game turns into blocks, and the jump targets become arrows — the labels disappear. There is no getting them back: on export to text the game will write numbers again.

So labels live exactly until the first time the program is opened in the block editor. That is no great loss — arrows are more reliable than numbers — but a program you keep in text form is better edited as text as well.

Where it comes in handy

• long programs written in an outside editor and pasted in whole;
• programs assembled by something else — a compiler targeting mlog, say: there labels are the only sensible way to refer to a place;
• portable pieces: a piece with labels can be pasted into the middle of somebody else’s program and nothing shifts.

Remember

• A line of the form name: is a label; it takes up no line number.
• jump name condition ... leads to the line after the label.
• They are understood by the game’s own parsing, not by external editors.
• There may be up to five hundred labels; a repeated name and a jump to nowhere are errors.
• In the block editor labels turn into arrows and disappear.

Task

Insert any line into the example — set empty 0, say — between set count 0 and the label. Nothing breaks: the jump still leads where it should.

Then rename the label to again2:, leaving jump again alone: the program will not assemble — the parser will say there is no such label.