Redundant­Imports

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 0) (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 write) (local x) (local y)) (write (list x (car (cdr (list x y))))) (newline)

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	REPL
Chibi	7	r7rs	okay	?	?
Chicken	9.0.1	r7rs	?	?	?
Foment	4 (debug)	r7rs	?	?	?
Gauche	9.4	r7rs	?	?	?
Kawa	0	r7rs	?	?	?
Larceny	98	r7rs	okay	rejected	okay
Petit Larceny	98	r7rs	okay	rejected	okay
Sagittarius	6.4	r7rs	?	?	?
Larceny	98	r6rs	okay	rejected	n/a
Petit Larceny	98	r6rs	okay	rejected	n/a
Petite Chez	4	r6rs	okay	rejected ?	n/a
Racket	1.1	r6rs	okay	rejected ?	n/a
Sagittarius	6.4	r6rs	okay	rejected ?	n/a
Vicare	3d7	r6rs	okay	rejected ?	n/a

The R6RS effectively forbids REPLs.

(I'll update this table when I next have access to my benchmarking machine.)