bugGforth - Bugs: bug #56406, Inconsistent Control structure...


bug #56406: Inconsistent Control structure mismatch reporting

Submitted by:  Phil Krylov <philkrylov>
Submitted on:  Tue 28 May 2019 12:07:58 PM UTC  
Category:  None Severity:  3 - Normal
Item Group:  None Status:  Invalid
Privacy:  Public Assigned to:  Bernd Paysan <paysan>
Open/Closed:  Closed

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Wed 29 May 2019 10:12:35 AM UTC, comment #2: 

Another way to express this:

: a if begin repeat ;

is a standard program, so Gforth as a standard system must accept it.

Why is it standard?  The standard says:

IF ( C: -- orig )
BEGIN ( C: -- dest )

So after BEGIN the control-flow stack contains ( orig dest ).  The standard also says:

REPEAT ( C: orig dest -- )

So REPEAT just consumes these two control-flow stack items, and there is no type mismatch or control-flow stack imbalance that would constitute an error.

What does A mean?  It means the same as:

: a if begin again then ;

This is not the most useful program, but it is also standard.

Anton Ertl <anton>
Project Administrator
Tue 28 May 2019 08:02:01 PM UTC, comment #1: 

WHILE is equivalent to IF  1 CS-ROLL, and correspondingly REPEAT is AGAIN THEN.

So when IF BEGIN AGAIN THEN is ok (means endless loop if the condition is met), so is IF BEGIN REPEAT, which is the equivalent. Maybe surprising, but as it follows the rules, we can't check against it.

Bernd Paysan <paysan>
Project AdministratorIn charge of this item.
Tue 28 May 2019 12:07:58 PM UTC, original submission:  

: a  if ;
*the terminal*:1: error: Control structure mismatch
: a  if ;
                                         0 $1016189E0 throw
glocals.fs:651:5                         1 $10162B2C8 ?struc
                                         2 $10160E3F8 ;-hook

: a if begin repeat ;  ok

Phil Krylov <philkrylov>


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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2019-07-15 paysan Open/ClosedOpen => Closed
    2019-05-28 paysan StatusNone => Invalid
        Assigned toNone => paysan

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