Re: Is multi-level function return possible?

George Neuner schrieb:


> The instruction cost is slightly greater to maintain a display than to
> maintain a static chain, but if the display is in suitably fast memory
> - in registers or locked into cache - the actual difference in *time*
> spent on maintenance may be insignificant.


Many years ago I found a funny implementation of local variables in
GfA-Basic. As opposed to most (all?) other compilers, on entry of a
subroutine the *global* variables; matching the name of a local
variable or parameter; were pushed onto the stack and re-initialized
for use inside the subroutine, and restored on exit. This allows to
access all currently living variables from everywhere in the code. It
also allows for by-name references when the table of variables is
prepared accordingly, as was the case in traditional Basic. Dunno how
Algol implemented this and its many other exotic parameter passing
conventions.


I found that implementation so exciting, that I think it's worth to be
mentioned here.


DoDi
[That's approximately what Lisp calls shallow binding. For Algol60
call by name, which was a mistake, it needed the Pascal display or the
equivalent, and arguments had to be callback routines (thunks) to
allow them to recompute the expression values. -John]

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