Unable to redefine imported symbols in r7rs library

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Issue #266 wontfix
Duy Nguyen created an issue

I found this while playing with some code from chibi. The simplified code is like this

(define-library (abc)
  (import (scheme base) (srfi 1))
  (export everyx)
    (define (every) #f)
    (define everyx every)))

and it fails to build

$ ./build/sagittarius -r7 -L . -e '(import (abc))'
Unhandled exception
  Condition components:
  1. &compile
    program: (import (abc))
    source: #f
  2. &compile
    program: (define-library (abc) (import (scheme base) (srfi 1)) (expor
    source: "/home/pclouds/W/sagittarius-scheme/abc.scm":1
  3. &syntax
    subform: (every)
    form: (define (every) #f)
  4. &message attempt to modify immutable variable
  5. &stack-trace

because “every” is already defined in (srfi 1) and I attempt to redefine it.

I have not read r7rs-small again, but I don’t think redefining symbols is forbidden. At least it used to work like that in r5rs. It’s not a competition, but as far I can test, Gauche, Chibi and Larceny all accept this code.

Comments (3)

  1. Takashi Kato repo owner

    Thanks for the report!

    It is an error to redefine the imported variables according to the R7RS section 5.2. Which means, raising an error is perfectly fine. As you mention, it’s not a competition, I don’t change the current behaviour since Sagittarius is one of the R6RS/R7RS implementations.

    NOTE: this must signal an error on R6RS.

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