174: Safe uses of multiple values

Currently, uses of values where the values are discarded anyway is illegal, but all the usual Schemes except SCM and SSCM accept them (I tested with begin). Should we go with something close to the R6RS wording?

"The continuations of all non-final expressions within a sequence of expressions, such as in lambda, begin, let, let*, letrec, letrec*, case, and cond forms, take an arbitrary number of values."

The definition of begin would need to change too:

(define-syntax begin (syntax-rules () ((begin exp) exp) ((begin exp1 exp2 ...) (call-with-values (lambda () exp1) (lambda args (begin exp2 ...))))))

cowan

2011-05-06 21:36:55

descriptionCurrently, uses of `values` where the values are discarded anyway is illegal, but all the usual Schemes except SCM and SSCM accept them (I tested with `begin`). Should we go with something close to the R6RS wording? "The continuations of all non-final expressions within a sequence of expressions, such as in `lambda`, `begin`, `let`, `let*`, `letrec`, `letrec*`, `case`, and `cond` forms, take an arbitrary number of values." Currently, uses of `values` where the values are discarded anyway is illegal, but all the usual Schemes except SCM and SSCM accept them (I tested with `begin`). Should we go with something close to the R6RS wording? "The continuations of all non-final expressions within a sequence of expressions, such as in `lambda`, `begin`, `let`, `let*`, `letrec`, `letrec*`, `case`, and `cond` forms, take an arbitrary number of values." The definition of `begin` would need to change too: {{{ (define-syntax begin (syntax-rules () ((begin exp) exp) ((begin exp1 exp2 ...) (call-with-values (lambda () exp1) (lambda args (begin exp2 ...)))))) }}}

arcfide

2011-05-08 02:59:44

I think using the term "any number" instead of "an arbitrary number" probably makes more sense, but other than that, I would go with it.

alexshinn

2011-07-10 21:46:00

resolution␣␣

statusnewdecided

We voted to adopt this.

cowan

2011-07-11 10:21:07

owneralexshinncowan

statusdecidedwriting

cowan

2012-10-09 00:46:02

resolution␣fixed

statuswritingclosed

Ticket 174: Safe uses of multiple values