[PDP8-Lovers] if you hadn't already known this about the PDP-8

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Thu Dec 13 15:58:59 2001

On Dec 13, 9:26, Mark Crispin wrote:

> Unique? Quite a few processors of that time had a store-PC-and-jump type
> subroutine call. The beloved PDP-10 had three (JSR, JSP, JSA/JRA) and
> subsequent enhancements added more (JSYS, XPCW); yet it also had stacks
> its inception.
> Contemporary programming languages, such as BASIC and FORTRAN, did not
> stack subroutines. It's possible that modern BASIC and FORTRAN compilers
> permit recursive subroutine calls, but doing so is still prohibited by
> language specification. Now you know why.

That's not wholly true; FORTRAN prior to FORTRAN-90 prohibits recursion but
it's a required feature in FORTRAN 90. I don't believe it's actually
prohibited in BASIC of the mid-to-late 60's. There were certainly
inplementations in the early 70s that allowed it, and it's a feature of the
modern standards (both de-facto and ANSI). Recursion was also a (required)
feature of ALGOL in 1958, and its successors, as was stack-based

However, in support of Mark, it's worth noting that the main reason there's
no recursion allowed in FORTRAN, and it almost was omitted from the
original ALGOL spec, was that it was hard for people to understand how it
could be implemented across a variety of architectures. Stacks had been
around since the mid-50s but lots of machines provided no specific support
for them.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Thu Dec 13 2001 - 15:58:59 GMT

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