R7RSSmallErrata.md

Errata from the final draft of R7RS. This list is unofficial.

1. In Section 3.1 (Variables, syntactic keywords, and regions), the claim in paragraph 2 that all variable binding constructs can be explained in terms of lambda does not apply to top-level bindings.

2. Section 7.1.5 (Transformers) doesn't make it clear that a top-level syntax-rules pattern must be a list pattern, not a vector pattern or an identifier pattern.

3. In Section 6.3 (Booleans), the procedure boolean=? is defined to return #t if the arguments are all booleans and are either all #t or all #f. The words "are all booleans and" incorrectly suggest that the value is #f if at least one argument is not a boolean. In fact it is an error to apply boolean=? to non-booleans.

4. In Section 4.1.2 (Literal expressions), the examples '# and # should be '#\a and #\a respectively.

5. In section 7.1.1 (Lexical structure), the escape sequence \| is not shown as permitted in . The list in Section 6.7 shows that it is equivalent to |. Similarly, the escape sequences \" and \\ should be allowed in . This makes the same escape sequences valid in both strings and symbols.

6. In Section 7.3 (Derived expression types), the syntax-rules definition of case is incorrect; the fourth syntax rule must be moved after the fifth to avoid an improper match against the fourth rule when => is present. Here is the correct version:

 (define-syntax case
   (syntax-rules (else =>)
     ((case (key ...)
        clauses ...)
      (let ((atom-key (key ...)))
        (case atom-key clauses ...)))
     ((case key
        (else => result))
      (result key))
     ((case key
        (else result1 result2 ...))
      (begin result1 result2 ...))
     ((case key
        ((atoms ...) => result))
      (if (memv key '(atoms ...))
          (result key)))
     ((case key
        ((atoms ...) => result)
        clause clauses ...)
      (if (memv key '(atoms ...))
          (result key)
          (case key clause clauses ...)))
     ((case key
        ((atoms ...) result1 result2 ...))
      (if (memv key '(atoms ...))
          (begin result1 result2 ...)))
     ((case key
        ((atoms ...) result1 result2 ...)
        clause clauses ...)
      (if (memv key '(atoms ...))
          (begin result1 result2 ...)
          (case key clause clauses ...)))))

7. In Section 7.1.1, the lexical rule incorrectly omits @.

8. Bibliographic reference ![13] should link to SRFI 4.

9. In section 4.2.2, add "interleaving evaluations with assignments" to the definition of letrec*. Replace the meaningless example with this:

;; Returns the arithmetic, geometric, and
;; harmonic means of a nested list of numbers
(define (means ton)
  (letrec*
     ((mean
        (lambda (f g)
          (f (/ (sum g ton) n))))
      (sum
        (lambda (g ton)
          (if (null? ton)
            (+)
            (if (number? ton)
                (g ton)
                (+ (sum g (car ton))
                   (sum g (cdr ton)))))))
      (n (sum (lambda (x) 1) ton)))
    (values (mean values values)
            (mean exp log)
            (mean / /))))

Note that evaluating (means '(3 (1 4))) returns three values: 8/3, 2.28942848510666 (approximately), and 36/19.

10. In section 7.1.5, add to the alternatives for the rule.

11. Section 1.3.4 refers to "the initial environment" containing *, which is not true for programs. It should refer instead to "an environment containing the base library".

12. An example in section 5.3.3 refers to integer-sqrt instead of exact-integer-sqrt.

13. In section 4.3.1, the body of a let-syntax expression is said to contain "one or more definitions"; it should be "zero or more definitions".

14. In section 6.6 for char-upcase/downcase/foldcase and 6.7 for string-upcase/downcase/foldcase the reader is referred to UAX #29, but it should be TR #44.

15. In section 7.3, the definition of case-lambda should use letrec-syntax, not let-syntax.

16. In section 4.3.2 (but not in 7.1.3), change <literal> to <pattern literal> to avoid confusion.

17. (removed, already in R7RS-small)

18. In the first bullet of the "Incompatibilities with R6RS" section, for "have to be be" read "have to be".

19. In numeric tower bullet of the "Incompatibilities with R6RS" section, for "but the R6RS procedures real-valued?, rational-valued?, and integer-valued? were not" read "but the semantics of the R6RS procedures real?, rational?, and integer? were not adopted. (Note that the R5RS/R7RS semantics are available in R6RS using real-valued?, rational-valued?, and integer-valued?)".

20. From Richard Kelsey's R5RS errata: In the explanation of list-ref, for "fewer than k elements", read "k or fewer elements". Thus, (list-ref '(x) 1) is an error.

21. In Appendix B, for "All algebraic operations except / produce exact values given exact inputs" read "The algebraic operations +, -, *, and expt where the second argument is a non-negative integer all produce exact values given exact inputs".

22. In Appendix A, the (scheme r5rs) library should export syntax-rules, else, ..., => and _.

23. In the definition of string-for-each, for "the elements of the lists" read "the elements of the strings".

24. The value of the example (real? 2.5+0.0i) in Section 6.2.6 is shown as #f, as in R6RS. This contradicts the prose explanation. No resolution of the conflict has been reached as yet.

25. In the definition of char-foldcase, the sentence "If the argument is an uppercase letter, the result will be either a lowercase letter or the same as the argument if the lowercase letter does not exist or is not supported by the implementation" is no longer appropriate as of Unicode 8.0, when folding began to convert Cherokee lower-case letters to upper case. Replace it with "If the result of folding is not supported by the implementation, the argument is returned".

26. In the definition of <feature requirement> in Section 7.1.7, for <library name> read (library <library name>).

27. The claim in the definition of current-second that the TAI-UTC offset as of January 1, 1970 was ten seconds is factually incorrect per the USNO's list of offsets. The correct value for that date is 8.000082 seconds.

28. The definition of char-numeric? refers to a nonexistent Unicode property Numeric_Digit. The intention was to refer to characters whose Numeric_Type property is Decimal, which is defined by Unicode as those which have a non-empty value in field 6 of the UnicodeData.txt file. This is equivalent to characters with a General Category of Nd. The simplest fix is to change the relevant paragraph of Section 6.6 from "Numeric_Digit" to "Numeric_Type=Decimal". (Note: R6RS uses the term "Numeric", which also is not a Unicode property.)

29. In Section 6.5 (Symbols), the procedure symbol=? is defined to return #t if all the arguments are symbols and all have the same names in the sense of string=. The words "are all symbols and" incorrectly suggest that the value is #f if at least one argument is not a symbol. In fact it is an error to apply symbol=? to non-symbols. This is directly analogous to erratum 3.

30. Notes that the categories Lu, Ll, ... Co that are valid in identifiers apply only to non-ASCII characters; the valid ASCII characters are given explicitly.

31. In section 1.1, the sentence "Each use of a variable is associated with a lexically apparent binding of that variable" appears. However, this is only true after macroexpansion, as the binding may be hidden in a user-written macro. Prefix the sentence with "After macros are expanded".

32. In the third paragraph of the definition of null-environment, the reference to scheme-report-environment should be to null-environment, and is changed accordingly.

33. In Section 4.3.3 (Signaling errors in macro transformers) the example simple-let macro does not do what it appears to do: it will only trigger the syntax-error if the incorrect binding form is the last binding form in the list.