7 Jun
2017
7 Jun
'17
4:58 p.m.
Michael Kjörling <michael(a)kjorling.se> wrote:
And https://www.bell-labs.com/usr/dmr/www/bcpl.pdf page 11 (PDF page
14) says:
> 4.7 Vector Applications
> /.../
> Semantics: A vector is represented by a pointer to a consecutive
> group of words which are the elements of the vector. The pointer
> points to the zeroth element.
That syntax is quite different from the later BCPL that I'm familiar with.
http://www.cl.cam.ac.uk/~mr10/bcplman.pdf
It has a ! indirection operator which can be both unary and binary, as in
old BCPL new BCPL C
lv x @x &x
rv ptr !ptr *ptr
ptr*[i] ptr!i ptr[i]
Richards' 1969 paper uses a down-arrow for binary !
You can use "manifest" constants for laying out a structure, e.g.
MANIFEST { car; cdr; }
declares car and cdr to have values 0 and 1. This lets you do struct-style
indirection using the same operator as for array indexing, like in this
function definition:
LET cadr(p) = p!cdr!car;
When I saw how ->integ is used in the 6th Edition kernel it felt very BCPL
to me.
Tony.
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