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*To*: rrrs-authors*Subject*: (not (eq? '() #f))*From*: will@cs.uoregon.edu*Date*: Tue, 27 Feb 90 16:13:52 PST

The poll conducted by Chris Haynes has revealed that the status quo is opposed by more people and supported by far fewer people than option D (that #F is distinct from the empty list, and the empty list counts as true in boolean contexts). Since unanimity cannot be achieved, option D appears to be the next best thing. I will therefore change the R3.99RS to reflect option D by making the changes indicated below. These changes will make R4RS consistent with the draft IEEE standard. Peace, Will section 3.2 Change: except for #f and possibly the empty list. To: except for #f. Delete the two sentences that follow this one. Change: to refer to any Scheme value that counts as true To: to refer to any Scheme value except #f Change: to refer to any Scheme value that counts as false. To: to refer to #f. section 3.4 Add null? to the list of predicates, and add emptylist to the list of types. section 6.1 Rephrase first two paragraphs as The standard boolean objects for true and false are written as #t and #f. What really matters, though, are the objects that the Scheme conditional expressions (if, cond, and, or, do) treat as true or false. Of all the standard Scheme values, only #f counts as false in conditional expressions. All other standard Scheme values, including #t, pairs, the empty list, symbols, numbers, strings, vectors, and procedures, count as true. Eliminate the rationale for allowing the empty list to count as false. Change the following examples as indicated: (not '()) ==> #f (not (list)) ==> #f (boolean? '()) ==> #f section 6.2 Change: , except that #f and the empty list are permitted to be identical. To: . section 6.3 Remove the note that follows the description of null? Notes: Language changes Add: The empty list is now required to be distinct from #f and to count as true in conditional expressions.

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