Re: [Scheme-reports] R7RS final draft - bug report for section 7.3 Derived expression types

On Sun, Sep 8, 2013 at 11:20 PM, Joseph Wayne Norton <norton@x> wrote:

Hello.

For R7RS final draft, the syntax-rules for the case derived _expression_ appears to be incorrect. The order of the 4th <syntax rule> is incorrect.

The 4th <syntax rule> should be moved after the 5th <syntax rule> . If not, the result1 pattern variable of the 4th <syntax rule> will incorrectly match with an => in the input.

Thanks Joseph, you are correct. We'll add this to the errata,

and I'll also add a case for this to the R7RS test suite, which

is currently only checking => for else clauses.

Best regards,

Joe N.

p.s. Here is a corrected 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 ...) result1 result2 ...))
- (if (memv key '(atoms ...))

- (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 ...)))))

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