Re: var parameters in T?

[rees@decwrl.ARPA (Jonathan Rees)]

    From: Mike Caplinger <mike@rice>
    Date:     Thu, 19 Jul 84 18:35:27 CDT

    Is there any way to cleanly do VAR parameters in T?  For example, I
    might expect the function

    (define foo (lambda (a) (set a 1)))

    when invoked with

    (lset c 0)
    (foo (locative c))

    to leave c with the value 1, but it doesn't.  Obviously I don't
    understand what locatives are doing for me...

T and Scheme and most Lisps are call-by-value where values are usually
references.  A locative is a value which is a reference to a reference.
To dereference a locative you need to use CONTENTS.  So maybe you want
to say

	(define (foo loc) (set (contents loc) 1))
	(block (foo (locative a)) a) => 1

This is exactly analogous to the situation in C (also call-by-value)
where if you say &, you need to say * on the other end:

	foo(loc) int *loc; { *loc = 1; }
	(foo(&a), a)  =>  1

Alternatively, you could use closures, which are a little lower-tech
than locatives:

	(define (foo proc) (proc 1))
	(block (foo (lambda (x) (set a x))) a) => 1

After all, (locative x) is just a shorthand for

	(object nil
		((contents self) x)
		(((setter contents) self) (lambda (val) (set x val))))

so why provide both assign and update functionality if you're only
going to use one or the other.