[Implemented] #PB_Label

[Hroudtwolf]

Hi,

A little wish again...
An #PB_Label option for Defined would be very helpful.


Best regards

Wolf

[Psychophanta]

I Second it

[freak]

Its not possible as labels can be used before they are declared, and PB is a one-pass compiler:

Code: Select all

CompilerIf Defined(mylabel, #PB_Label) ; how do we know there will be a "mylabel:" later ?
CompilerEndIf

; ...

mylabel: 

[netmaestro]

I thought I understood the one-pass compiler concept until I realized one day that while I can't do this:

Code: Select all

DoIt()

Procedure DoIt()
  ; do something
EndProcedure

without having the procedure declared first, which makes perfect sense, why is it that I can do this:

Code: Select all

CatchImage(0, ?label)

; lots of lines of code

DataSection
  label: Includebinary "image.bmp"
EndDataSection

when, due to the one-pass operation, the compiler seemingly shouldn't know where ?label is?

There must be something I'm missing, as this has puzzled me for quite a long time.

[Fred]

Actually, "?" operand only work with a label, so we "pre-declare" the label (and check for real declaration at the very end of the program). That's a little exception, that's true.

[freak]

For procedures, the compiler has to know the parameters and returntype
to generate the right code and show correct error messages.

For labels all that isn't needed, thats why it is possible to simply assume the label exists
and fire an error at the very end if it isn't found.

[edit] must type faster...

[Hroudtwolf]

It's a great pity.
But, thanks for the explanations.

[Psychophanta]

I believed that labels just was treated as simple long type variables (pointers) internally.
Maybe if there was like that, things would be easier.

[Psychophanta]

ehh! look at this:

Code: Select all

If Defined(var,#PB_Variable)
  Debug "yes":Else:Debug "nope"
EndIf
var.l

nope, but

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var.l
If Defined(var,#PB_Variable)
  Debug "yes":Else:Debug "nope"
EndIf

yes.
So:

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If Defined(var,#PB_Label)
  Debug "yes":Else:Debug "nope"
EndIf
var:

should be nope, but:

Code: Select all

var:
If Defined(var,#PB_Label)
  Debug "yes":Else:Debug "nope"
EndIf

should be yes. Respected the one compilation pass

[freak]

That would be very inconsistent:

Code: Select all

x = ?mylabel ; perfectly valid

Debug Defined(mylabel, #PB_Label) ; returns 0, even though mylabel is accessible !?

mylabel:

As i said, labels are quite different from other things in PB.
Since a label can be accessed before it is defined, Defined() should also reflect this,
but this isn't possible.

[Psychophanta]

But... if compiler knows what is ?mylabel , why some like this couldn't work?

Code: Select all

x = ?mylabel ; perfectly valid

Debug Defined(?mylabel, #PB_Label)
mylabel:

[freak]

read the full post please. Fred and I explained it... :roll:

[pcfreak]

wouldn't it be possible to let the fasm compiler handle this, like converting the Defined() command for this case to asm macro instructions

!if defined label
debug "label defined"
!else
debug "label undefined"
!end if

well.. would be the 'dirty' way but possible i think.. don't know atm how pb defines labels intern and can't check 'cause i'm at uni atm :p