Scheme - What is letrec* ?

Author

What is letrec* ?

Andrew Wilcox

2004-12-07, 4:04 pm

I noticed in the revised progress report on R6RS
(http://schemers.org/Documents/Stand.../2004-10-13.pdf), one of
the extensions under consideration is to "add letrec*, and define
internal =define= in terms of it".

What is letrec* ? Is it simply a letrec with the init expressions
evaluated in a specific left-to-right order?

In a letrec*, can later variables depend on the values of earlier
values? For example, with internal =define='s defined with letrec*,
would the following work or not?

(let ()
(define (add-10 x) (+ x 10))
(define ten (add-10 0))
(define twenty (add-10 ten))
(list ten twenty))

Thank you,

Andrew Wilcox
email: scheme[at]andrewwilcox.name

Michael Sperber

2004-12-07, 4:04 pm

>>>>> "Andrew" == Andrew Wilcox <scheme@andrewwilcox.name> writes:

Andrew> What is letrec* ? Is it simply a letrec with the init expressions
Andrew> evaluated in a specific left-to-right order?

Yes.

Andrew> In a letrec*, can later variables depend on the values of earlier
Andrew> values?

Yes.

Andrew> For example, with internal =define='s defined with letrec*,
Andrew> would the following work or not?

Andrew> (let ()
Andrew> (define (add-10 x) (+ x 10))
Andrew> (define ten (add-10 0))
Andrew> (define twenty (add-10 ten))
Andrew> (list ten twenty))

Yes.

--
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla

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