RETURNing from GOSUB inside a function does not work correctly

12Me21Created: ~7 years ago

On the other thread, some~~one~~ idiot pointed out that RETURN doesn't work as you'd expect in functions that return things:

DEF EXAMPLE()
 GOSUB @TEST
 RETURN "666"
 
 @TEST
 RETURN
END
PRINT EXAMPLE()

This gives an uninitialized variable used error at the second RETURN. However, if you give a value that is the same type as the real return value:

DEF EXAMPLE()
 GOSUB @TEST
 RETURN "666"
 
 @TEST
 RETURN ""
END
PRINT EXAMPLE()

Then it will work just as expected.

~7 years agoEdited ~7 years ago by 12Me21

hakke #2

someone?

Spoiler

you bastard

~7 years ago

12Me21 #3

Ok, I finally figured out why this happens. When RETURN is used in a function that returns a value (That is, a function defined as DEF NAME(...)), it does two things. First it sets the value of a hidden OUT variable, and then it exits the function.

DEF TEST()
 RETURN 6
END
'this is the same as:
DEF TEST OUT X
 X=6
 RETURN
END

When making the changes to allow RETURN to return from a GOSUB if nessesary, they stopped it from exiting the function, but it still sets the value of that hidden OUT variable! OUT variables can only have their type changed once, so this causes a type mismatch:

DEF EXAMPLE()
 GOSUB @TEST
 RETURN 7 'type mismatch
 
 @TEST
 RETURN "HELLO"
END

Is the same as

DEF EXAMPLE OUT X
 GOSUB @TEST
 X=7 'can't make X into a number because it's a string now
 RETURN 'return from function

 @TEST
 X="HELLO"
 RETURN 'return from GOSUB
END

~6 years ago

SquareFingers #4

some~~one~~ idiot

Well, that's rather unkind.

~6 years ago