Re: A different stack discipline

["Hugo Hörnquist" <hugo@lysator.liu.se>]

The section, as far as I can see, just describes a machine
which pushes continuation instead of the PC counter to the
stack.

Also, while in theory quite nice it has the problem that
Guile is really slow in restoring continuations, due to the
fact that we have complete C interoperability.

On Wed, Oct 31, 2018 at 09:55:06PM +0100, Mikael Djurfeldt wrote:
> I've looked a little at the Guile vm and compiler.
> 
> What a beautiful work! It also has very nicely written documentation. Very
> impressive!
> 
> Here's an idea/question:
> 
> SICP describes a register machine with a stack discipline which is
> different from most machine models in that it doesn't have a call
> instruction which pushes the PC onto the stack and a return instruction
> which pops it. Instead it has a continue register: When calling a
> subroutine, you load the continue register with the continuation of the
> subroutine (as described here:
> https://mitpress.mit.edu/sites/default/files/sicp/full-text/book/book-Z-H-31.html#%_sec_5.1.4
> ). A subroutine ends with a branch to its continuation (stored in the
> continue register).
> 
> It seems to me that this 1. is natural to scheme since tail recursion
> doesn't need to be handled differently than ordinary calls, 2. that it fits
> the Guile compiler nicely with its CPS soup and 3. that it possibly could
> save vm instructions and stack space.
> 
> Could it be a good idea to switch over to the SICP stack discipline in the
> vm?
> 
> Best regards,
> Mikael D.

-- 
hugo