From: already5chosen@yahoo.com   
      
   On Wed, 5 Nov 2025 17:26:44 +0200   
   Niklas Holsti  wrote:   
      
   > On 2025-11-05 7:17, Anton Ertl wrote:   
   >   
   >     [ snip ]   
   >   
   > > Yes, assigned goto and labels-as-values (and probably the Cobol   
   > > alter/goto and PL/1 label variables) are there because computer   
   > > architectures have indirect branches and the programming language   
   > > designer wanted to give the programmers a way to express what they   
   > > would otherwise have to express in assembly language.   
   > >   
   > > Why does standard C not have it?  C had it up to and including the   
   > > 6th edition Unix <3714DA77.6150C99A@bell-labs.com>, but it went away   
   > > between 6th and 7th edition.  Ritchie wrote   
   > > <37178013.A1EE3D4F@bell-labs.com>:   
   > >   
   > > | I eliminated them because I didn't know what to say about their   
   > > | semantics.   
   > >   
   > > Stallman obviously knew what to say about their semantics when he   
   > > added labels-as-values to GNU C with gcc 2.0.   
   >   
   >   
   > I don't know what Stallman said, or would have said if asked, but I   
   > guess something like "the semantics is a jump to the (address of the)   
   > label to which the value refers", which is machine-level semantics   
   > and not semantics in the abstract C machine.   
   >   
   > The problem in the abstract C machine is a "goto label-value"   
   > statement where the label-value refers to a label in a different   
   > function. Does gcc prevent that at compile time? If not, I would   
   > expect the semantics to be Undefined Behavior, the usual cop-out when   
   > nothing useful can be said.   
      
   Yes, UB sounnds as the best answer.. Inter-procedural assigned goto is   
   not different from out-of-bound array access or from attempt to use   
   pointer to local variable when the block/function that originally   
   declared the variable is no longer active.   
   But compiler shall try to detect as many cases of such misuse as it can.   
      
   >   
   > (In an earlier discussion on this group, some years ago, I explained   
   > how labels-as-values could be added to Ada, using the type system to   
   > ensure safe and defined semantics. But I don't think such an   
   > extension would be accepted for the Ada standard.)   
   >   
   > Niklas   
      
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