Newsgroups: comp.lang.pop

In article ... axs@cs.bham.ac.uk (Aaron Sloman) writes:

   In Pop-11 if you want to evaluate a bit of text to get one element
   you have to do just:

       [%f(x)%]

   It's much easier where the default is quotation to have a single
   pair of brackets to unquote, than when the default is evaluation and
   lots of quotation marks are needed to quote. Of course, in Lisp you
   don't need lots of quotation marks as a prefix quotes the whole list
   expression.

In Pepper I have taken the step Steve describes: the list and vector syntax do
*not* automatically quote. (Why should they?) You want quotation, you quote
things, and a natural extension to Pop word-quotation is to allow *any* number
of items between quotes.

Thus the Pop list [bill and ben the flowerpot men] becomes the Pepper list
["bill and ben the flowerpot men"]. This means that it is not the case that
``lots'' of quotation marks are needed to quote, at least in examples like
this. 

It gets a bit more irritating in expressions like:

    [
	["bill and ben and little weed"],
	["andy and teddy and looby loo"],
	["thomas the tank engine and friends"]
    ]

but not, I think, significantly more so. As a quick bit of false statistics,
I went through about 13K lines of Pop in my Play directory. Just over 1100
lines had list brackets (excluding lines using []); 380 of those used % and 279
used ^, so well over half of those lists needed unquoted material in them.
(Only 141 lines used vector brackets, with unquotes appearing in over 90 of
those lines.)

NOTE WELL these figures are distorted by multi-line expressions and multiple
expressions per line. But they are suggestive.

Now you can get irritated (and I did) by the result of separating list and
vector syntax from quotation; sometimes, when you want to build a list that is
a mixture of quoted and unquoted material, it is a nusiance. But this is true
in Pop, too. And I will admit, I did spoil the purity of my position by
extending the quotation syntax to allow lists, vectors, and unquoted material
to appear within it. But the result -- that dropping into quotation mode is
signalled explicitly by quotation marks, which happen to allow list and vector
constructs within them -- is, I think, a rather nicer design.

   Probably one of the most serious misdesigns is that there's no good
   syntax for defining procedures that take different combinations of
   arguments, like, for example, newanyarray or newarray. You have to
   write horrible code to test what's on the top of the stack.

Well ... I think the horrid code warns us about the horrid idea. I've always
been unhappy about procedures like newarray *because* they take different
numbers of arguments, the number being determined by the types of the ``fixed''
arguments. I think this is one place where the open stack can become a road to
hell. (I'm happy with procedures that take a counted argument, such as
consstring; I'm less happy with consword, even though I implemented the same
interface in Pepper -- partly for efficiency in the lexical analyser! Perhaps
the advent of a suitable typechecker will assuage my fears. But more of that in
another note, probably after Christmas.)

PS When I left him, Steve was just coming to the boil.

   We need a syntax that uses patterns to handle the different cases.
   (Like prolog?)
--

Regards, Kers | "Once   I would have been glad   to have made your acquaintance
Renaissance:  | Now   I feel the danger   brought about   by circumstance."