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Using a substack as a library stack
Posted: Fri Jun 21, 2019 1:35 pm
by 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:
Code: Select all
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
Code: Select all
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
Re: Using a substack as a library stack
Posted: Fri Jun 21, 2019 1:56 pm
by 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
Re: Using a substack as a library stack
Posted: Fri Jun 21, 2019 2:01 pm
by bogs
scruffycoder wrote: ↑Fri Jun 21, 2019 1:35 pm
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
Re: Using a substack as a library stack
Posted: Fri Jun 21, 2019 4:05 pm
by dunbarx
Hi.
Welcome.
There are no stupid questions. Only stupid answers.
Craig
Re: Using a substack as a library stack
Posted: Fri Jun 21, 2019 6:08 pm
by 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.
Re: Using a substack as a library stack
Posted: Fri Jun 21, 2019 6:48 pm
by 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
Re: Using a substack as a library stack
Posted: Sat Jun 22, 2019 5:28 pm
by 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
Re: Using a substack as a library stack
Posted: Sat Jun 22, 2019 8:45 pm
by 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