p-Code environments

[Christian Corti]

On Wed, 6 Aug 2008, Ethan Dicks wrote:
> On Wed, Aug 06, 2008 at 01:25:40PM -0400, Paul Koning wrote:
>> By the way, I meant to mention another compiler that did something
>> like P-code: RT-11 Fortran.  The actual scheme was called "threaded
>> code" because it was basically a stream of function pointers.  (Come
>> to think of it, that's a common Forth encoding as well.)  That's about
>> as fast as straight code if most of what you need is calls to support
>> functions, and more compact because you're not including the opcode
>> word.
> That scheme sort of reminds me of FORTRAN IV for the PDP-8 - IIRC, the
> compiler produces, mostly, a stream of FPP instructions that either get
> executed by a real FPP-12 (or FPP-8?) _or_, lacking math hardware, get
> emulated by wads of PDP-8 instructions.
>
> The difference is rather than a stream of function pointers, it's a
> stream of math co-processor instructions that are either executed by
> real hardware or by an emulator library.  In either environment, though,
> the object code is the same.

And this all is similar to what compilers did in the 50s. The ACT-V 
compiler (ACT-I and ACT-III, too) simply generates a stream of runtime 
system calls (the runtime system is called 'basic subroutines'). You can 
even compile your program by hand since these subroutine calls are 
documented in the manual.

Christian