From: user5857@newsgrouper.org.invalid   
      
   EricP  posted:   
      
   > Anton Ertl wrote:   
   > > Stephen Fuld  writes:   
   > >> No, and I defer to you, or others here, on how these features are   
   > >> implemented, specifically whether code modification is required.  I was   
   > >> referring to features such as assigned goto in Fortran, and Alter goto   
   > >> in Cobol.   
   > >   
   > > On modern architectures higher-order functions are implemented with   
   > > indirect branches or indirect calls (depending on whether it's a   
   > > tail-call or not); likewise for method dispatch.   
   > >   
   > > I do not know how Lisp, FORTRAN, Algol 60 and other early languages   
   > > with higher-order functions were implemented on architectures that do   
   > > not have indirect branches; but if the assigned goto was implemented   
   > > with self-modifying code, the call to a function in a variable was   
   > > probably implemented like that, too.   
   >   
   > What architecture cannot do an indirect branch, which I assume   
   > means a branch/jump to a variable location in a register?   
      
   PDP-8, 4004, IBM 650, ... And any machine without "registers".   
      
   > And how would the operating system on such a machine get programs running?   
      
   Load them at a known location and branch to the known location.   
      
   > Even if an ISA did not have a JMP reg instruction one can create it   
   > using CALL to copy the IP to the stack where you modify it and   
   > RET to pop the new IP value.   
      
   Pure stack machines did a lot of this.   
      
   --- SoupGate-Win32 v1.05   
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