Boris Schaefer <firstname.lastname@example.org> wrote:
| What about:
| ((lambda ()
| (define x 3)
| (define y 2)
| (define z (* x y))
| As R5RS says:
| The <expression>s are evaluated sequentially from left to right, and
| the value(s) of the last <expression> is(are) returned. This
| expression type is used to sequence side effects such as input and
| So, I would think the above is equivalent to (local ...), as the begin
| guarantees that the internal defines are evaluated sequentially. Or
| am I still missing something?
Yes, you're still missing something, I'm afraid. Internal definitions
are not themselves "expressions", they're "internal definitions" --
and as such are *exactly* equivalent to a *single* "letrec" expression.
[See R5RS Section 5.2.2 "Internal definitions".] That is, your example
above is *defined* to mean this:
(begin ; now redundant
(letrec ((x 3)
(z (* x y)))
The "begin" contains only one expression (the "letrec"), and thus there
is no "left to right" sequentiality involved at all.
Oh, and the "letrec" bindings violate the rules [R5RS 4.2.2 & 5.2.2]
requiring that "it must be possible to evaluate each <init> without
assigning or referring to the value of any <variable>"...
Rob Warnock, 41L-955 email@example.com
Applied Networking http://reality.sgi.com/rpw3/
Silicon Graphics, Inc. Phone: 650-933-1673
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