Using a substack as a library stack

[scruffycoder]

Hi All,

Sorry if this is a stupid question, but I’ve really been struggling to get a library stack working within a main stack. Basically I want to add some code to a substack and call it from the main stack, Here’s what I did based on what I’ve been able to find so far.

1. Created a new stack called MainApp
2. Added a substack this this called ScriptStack
3. In the script of ScriptStack I created a simple function like this:

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function sayHelloWorld
put "Hello World"
end sayHelloWorld

4. In the UI of MainApp I added a button and added this code to its script:
on mouseUp pButtonNumber

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start using stack "ScriptStack"
sayHelloWorld
end mouseUp

I thought that I’d be able to access the sayHelloWorld function like I have tried to do here, but I keep getting this error in the button script:

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button "Button": execution error at line 4 (Handler: can't find handler) near "sayHelloWorld", char 1

I’m pretty sure I must be doing something daft, but I have read a few posts and articles on the web which suggest that this should work.

Any help which can be offered would be gratefully received.

Many thanks

[Klaus]

Hi scruffycoder,

welcome to the forum!

Well you wrote "function" but in fact this is more a command!
You can either write:

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command sayHelloWorld
   put "Hello World"
end sayHelloWorld

Of if you really want to use it as a function you have to use the "function" syntax in your "mouseup" handler:

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function sayHelloWorld
   put "Hello World"
end sayHelloWorld

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on mouseUp pButtonNumber
   get sayHelloWorld()
   ## or
   ## put sayHelloWorld() into the_dummy_var
  
   ## A function is meant to RETURN something, even if it actually doesn't 8-)
   ## So this syntax is neccessary.
end mouseUp

Best from germany

Klaus

[bogs]

Sorry if this is a stupid question,

I don't think it was stupid at all, I think it was an excellent question, and it gave Klaus a chance to clearly outline the differences between a function and a command.

It is almost always the nuances like this that make programming interesting

[dunbarx]

Hi.

Welcome.

There are no stupid questions. Only stupid answers.

Craig

[scruffycoder]

Thanks so much for the warm welcome and encouragement everyone and thanks Klaus for the excellent explanation. I’ve had quite a few abortive attempts at switching to Livecode but this kind of thing has always got in my way and forced me to switch back to more familiar languages.

[dunbarx]

Hi.

Know you can return a value from a command call as well as from a function call, but this is rarely done. The "return" control structure works in both. In a function:

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on mouseUp
   answer ultimateAnswer (6,9)
end mouseUp

function UltimateAnswer a,b
   put a * b into irrelevant
   return 42
end UltimateAnswer

In a command:

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local lifeTheUniverseAndEveryThing

on mouseUp
   put 6 * 9 into ultimateQuestion
   ultimateAnswer ultimateQuestion
   answer lifeTheUniverseAndEveryThing
end mouseUp

on UltimateAnswer irrelevant
   put 42 into lifeTheUniverseAndEveryThing
   return lifeTheUniverseAndEveryThing
end UltimateAnswer

The return here is not internally connected to its calling handler, as it is in a function call, so more stuff is required, like a script local variable so LC knows what is where. Just trivia...

Craig

[jacque]

The return here is not internally connected to its calling handler, as it is in a function call, so more stuff is required, like a script local variable so LC knows what is where.

Actually, when used in a command handler, the caller can get the value in the result. That way you don't need a storage variable or property.

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on mouseUp
   put 6 * 9 into ultimateQuestion
   ultimateAnswer ultimateQuestion
   put the result into tAnswer
   answer tAnswer
end mouseUp

on UltimateAnswer irrelevant
   put 42 into lifeTheUniverseAndEveryThing
   return lifeTheUniverseAndEveryThing
end UltimateAnswer 

[dunbarx]

Jacque.

True, certainly.

But the extra line to access the function "the result" is still an extra step, just like having to declare a local variable.

My point being that a function call needs neither.

Craig