In article ,   
   Hans Bezemer   wrote:   
   >On 09-01-2025 13:42, dxf wrote:   
   >>> There is no guarantee that a saved interpreter pointer on the   
   >>> stack is an execution token.   
   >   
   >Nope - in ANS-Forth it is listed as:   
   >   
   >nest-sys; definition calls; implementation dependent   
   >   
   >So - that's obvious. But in 4tH it works out. And defining it as >R   
   >works out as well. BTW, I've tested the thing - and it holds up.   
   >   
   >I got my work cut out for a next episode! On co-routines! ;-)   
   >   
   >Hans Bezemer   
   >   
   >BTW, I've heard there are implementations where nest-sys aren't even on   
   >the return stack. The standard seems to confirm this:   
   >   
   >return stack:  A stack that _MAY_BE_ used for program execution nesting,   
   >do-loop execution, temporary storage, and other purposes.   
   >   
   >.. and sorry to spoil the fun, but what we're doing here is illegal anyways:   
   >   
   >"A program shall _NOT_ access values on the return stack (using R@, R>,   
   >2R@ or 2R>) that it _DID_NOT_ place there using >R or 2>R;"   
   >   
   >In other words: your mileage may (be) very, very illegal.   
      
   The use of CO / ;: can't be illegal. Its implementation may not be   
   portable, that is another matter.   
   There is no reference  to the return stack in the glossary of CO.   
      
   ========================   
    CO   
      
   STACKEFFECT:   
      
   DESCRIPTION: []   
      
   Return to the caller, suspending interpretation of the current   
   definition, such that when the caller exits, this definition is   
   resumed. The return stack must not be engaged, such as between >R and   
   R> , or DO and LOOP .   
      
   GLOSSARY INDEX   
      
   SEE ALSO: CONTROL   EXIT   
   ========================   
   Merely a warning that the ciforth implementation doesn't work well with   
   certainly manipulations of the return stack.   
      
   The strict forbidden of nested definitions is non-sensical,   
   I allow nested definitions in ciforth with an extension.   
   : aap { : add + ; ]  1 2 add 3 4 add * ;   
   The program is non-standard, but if this extension is loaded the Forth   
   is still conforming.   
      
   >   
   >Hans Bezemer   
   >   
      
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