Passing a label name to another label as a parameter? [solved]

[trailsiderice]

So, at the start of each chapter in my game, I want to call a label that does a few things like stop the music and show a chapter title card, and to avoid having to copy and paste this same label multiple different times, I'd like to be able to call a single label and just swap out certain things like the chapter title and such as well as the label it jumps to when it's done. Problem is, I can't figure out how to pass the name of the next label as a parameter.

here's what I've got:

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    jump startlabel

I tried calling the label like this:

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call chapterintro("CHAPTER 01",chapter01_intro)

but I got an error telling me that chapter01_intro isn't defined.
so I tried calling the label like this:

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call chapterintro("CHAPTER 01","chapter01_intro")

but then I got an error telling me it couldn't find the label "startlabel".
I also tried doing both after changing the "jump" in chapterintro to "call", but no dice there either.

is this possible? how do you do this?
if it's not possible, then what's even the point of being able to pass parameters to a label?

[trailsiderice]

ok well i figured it out, sort of, but i'm having problems with it that I can't figure out how to fix.

i did it like this instead:

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$ renpy.call(startlabel)

but now i have a new problem.

I start chapter one with call chapterintro("CHAPTER 01","chapter01_intro")
then at the start of the next chapter, i call it again for chapter 2, and then again for chapter 3, and so on.
The problem arises when I reach the end of the chapters, and there's no more left. Expected behavior would be that the game ends and exits to main menu. But that's not what happens. Instead, it calls the chapter intro again... for each of the previous chapters in reverse order, essentially playing the whole game again backwards chapter by chapter.

How do I stop it from doing this?

[trailsiderice]

i feel like the potential solution might be somewhere in this section of the documentation:

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If the optional from clause is present, it has the effect of including a label statement with the given name as the statement immediately following the call statement. An explicit label helps to ensure that saved games with return stacks can return to the proper place when loaded on a changed script.

but i'm having trouble parsing this. i have no idea what this is supposed to mean, it's word salad to me, and there aren't any examples in the documentation. (this is a frequent problem i have with the documentation.. it can be quite oddly worded sometimes and provides very few clarifying examples)

can someone translate?

[trailsiderice]

OK, i think i've finally figured it out, for real this time.

that from statement section of the documentation still reads like word salad to me, but i don't think it's actually relevant in this case.
I was able to solve it by simply putting the statement "return" after the call chapterintro("CHAPTER 01","chapter01_intro") statement. I think the problem is that it was putting the entire first label of the chapter into the call stack, since there was no statement between the call and the first label in the chapter.

I would however still like an explanation of the from clause bit... that warning in the documentation about saves being broken or something if there's no from clause has me a little worried, i'd prefer not to have this setup break people's saves

[Another_Tom]

here's what I've got:

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    jump startlabel

Would you like to use jump or call? "expression" should work in both cases:

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    jump expression startlabel

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    call expresson startlabel
    ## After a return from the startlabel, the code is continued at this point.
    # so do a jump here or whatever you want to do.

[Alex]

So, at the start of each chapter in my game, I want to call a label that does a few things like stop the music and show a chapter title card, and to avoid having to copy and paste this same label multiple different times, I'd like to be able to call a single label and just swap out certain things like the chapter title and such as well as the label it jumps to when it's done. ...

The idea of call statement is to be able to run the same label several times from different places and easily return back. So, try to redesign your code a bit.
Make a label that you'll need and end this label with return statement.
Then, call this label wherever you need it - game will be returning to the line right after call, so you can put jump there or just continue the game flow.

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label some_label_to_call:
    "do stuff"
    return

label start:
    "..."
    call some_label_to_call
    "... ..."
    call some_label_to_call
    jump the_other_label
    "we won't see this line..."

label the_other_label:
    "the end"

[trailsiderice]

here's what I've got:

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    jump startlabel

Would you like to use jump or call? "expression" should work in both cases:

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    jump expression startlabel

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label chapterintro(chapter,startlabel):
    stop music 
    show screen chapter_titlecard(chapter) with fade
    call expresson startlabel
    ## After a return from the startlabel, the code is continued at this point.
    # so do a jump here or whatever you want to do.

I was mostly trying to use whichever one would actually work the way I wanted it to, I was trying both of them.
I didn't know about using expression though, that's good to know, thanks!