What does a ^ with no leading function name mean in mumps

Question

I have a piece of mumps code

DO ENYA^PRCTQUES

and

DO ^PRCTQUES

I understand what the first one does. However, I don't know what the 2nd example does. What's it calling?

EDIT - What if the code at the top is all comments?

PRCTQUES ; comment
  ;;comment
  ; MOAR comment
  ;

So what are we doing here with DO ^PRCTQUES ? Just making sure the file exists and is compiled?

Finally what if my file started with the label ZOOT?

ZOOT
   (code)
  Q

then what? Does DO ^PRCTQUES invoke the ZOOT label because it is at the top? Or do I get an error message? It looks like bad style of course...

Answer 1

If you have a routine FOO that looks like this:

FOO ; Foo routine
 WRITE "HELLO FOO",!
 QUIT
LABEL ; A line label
 WRITE "HELLO LABEL",!
 QUIT

DO ^FOO will show the output "HELLO FOO". DO LABEL^FOO will show "HELLO LABEL".

So calling a routine without a label (as in DO ^PRCTQUES) will execute the routine from the top. Otherwise, with a label DO ENYA^PRCTQUES it will run the code starting from the label.

In your edited question, you asked about what happens if you have a routine PRCTQUES with a label ZOOT at the top. Like this:

ZOOT
 WRITE "ZOOT",!
 QUIT

In this case, DO ^PRCTQUES will write ZOOT. Also, DO ZOOT^PRCTQUES will also write ZOOT. However, because most companies consider it a bad practice that the first label in the routine isn't the routine name, so this is not an example you see in practice.

Answer 2

According to Wikipedia:

All variable names prefixed with the caret character (^) use permanent (instead of RAM) storage, will maintain their values after the application exits, and will be visible to (and modifiable by) other running applications.

https://en.m.wikipedia.org/wiki/MUMPS