Redundant imports

Importing two or more different libraries that export the same identifier with the same binding is okay in both R7RS and R6RS libraries and programs. Importing the same identifier with different bindings is an error in R7RS and signals an error in R6RS systems, but should be permitted by an R7RS REPL (R7RS section 5.2). This is tested by the following program:

(define-library (local xy)
  (export list car cdr x y)
  (import (scheme base))
   (define x 101)
   (define y 202)))
(define-library (local x)
  (export car x)
  (import (scheme base) (local xy)))
(define-library (local y)
  (export cdr y)
  (import (scheme base) (local xy)))
(import (scheme base) (scheme write) (local x) (local y))
 (write (list x (car (cdr (list x y)))))

For R6RS, change define-library to library, (scheme base) to (rnrs base), and (scheme write) to (rnrs io simple). To test different bindings, add new definitions of x and y to (local x) and (local y) respectively.

system version mode same binding different binding different binding in REPL
Chibi 0.7 r7rs okay bug? bug?
Chicken r7rs okay warned okay
Foment 0.4 (debug) r7rs bug? bug? bug?
Gauche 0.9.4 r7rs okay accepted okay
Kawa 2.0 r7rs okay rejected okay
Larceny 0.98 r7rs okay rejected okay
Petit Larceny 0.98 r7rs okay rejected okay
Sagittarius 0.6.4 r7rs okay rejected rejected
Larceny 0.98 r6rs okay rejected n/a
Petit Larceny 0.98 r6rs okay rejected n/a
Petite Chez 8.4 r6rs okay rejected n/a
Racket 6.1.1 r6rs okay rejected ? n/a
Sagittarius 0.6.4 r6rs okay rejected n/a
Vicare 0.3d7 r6rs okay rejected n/a

The R6RS effectively forbids REPLs.

In some cases, indicated by "bug?", the observed behavior appears to indicate a bug that's unrelated to the issue tested here.

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