🚀 go-pugleaf

In article ... throopw@sheol.UUCP (Wayne Throop) writes:

   :: From: kers@hplb.hpl.hp.com (Chris Dollin) writes:
   :: Message-ID: <KERS.92Nov12085629@cdollin.hpl.hp.com>
   :: [...]  define 5 ++( x, y ); lvars x, y; x + y + 1 enddefine; [...]
   : From: hrubin@pop.stat.purdue.edu (Herman Rubin)
   : Message-ID: <BxMCxA.3nM@mentor.cc.purdue.edu>
   : [...] I would accept that as the insertion of the ++ operator.

   :: (Pop is an open-stack language), ``x * y'' means ``push x, push y,
   :: call -'', and ``f(x)'' means ``push x, call f''.
   : But I would object to any language which insists that we use a
   : strictly stack machine.  Pushing, popping, and calling are to be
   : avoided unless necessary.  Otherwise things just run too slowly to be
   : of more than theoretical use.

   This is yet another case of confusing the abstract notation with a
   concrete implementation.  Just because the abstract semantics has the
   model of a stack is NO reason to suppose that this forces one to
   implement the model using an explicit stack with explicit push and pop
   operations.  (Not being intimately familiar with Pop, it may be that
   Pop *does* require an explicit stack in the implementation, but that
   can't be told just from what Chris said.  ...............

It is, perhaps, unfortunate in this instance that Pop's model makes it rather
hard for an implementation to avoid actually having a stack. When calling
system procedures (those things often thought of as ``built-ins'', like ``+''
and ``=''), it should be easy enough to pass parameters via registers, rather
than on the value stack. However, when calling user procedures, this is much
more difficult; you don't know how many arguments they take, how many results
they return, or indeed what procedure they *are* (since, by default, they're
all variables to allow for incremental development and redefinition).

So, the Pop compiler is free to eliminate stack use where it can prove its not
necessary. It's just that the proofs are, in general, impossible.

Any more Pop questions should be taken to comp.lang.pop.



--

Regards | "Always code as if the guy who ends up maintaining your code will be
Kers.   | a violent psychopath who knows where you live." - John F. Woods