在DrRacket中使用R5RS方案排序

Question

I'm learning scheme using DrRacket version 7.0.

I have copied, and modified, the following procedure from this SO answer .

#lang racket

(define sort-asc-by-second
  (lambda (lst)
    (sort lst
          (lambda (x y) (< (cdr x) (cdr y))))))

And it works perfectly.

Now I have change the #lang racket instruction with this one #lang r5rs .

And DrRacket complains with the following error:

sort: unbound identifier in: sort

Do I forget to add something to DrRacket (libraries, modules, etc.)? Or maybe sort is not available in R5RS.

Answer 1

According to the R5RS report there is no such thing as sort . You may fetch the reference implementation for sort from SRFI-95 Sorting and merging . It's not 100% compatible with the #lang racket one. R5RS doesn't have libraries so the portable way would be to load it or inline it.

R6RS has superseded R5RS and it has list-sort in its standard library.

R7RS-Large, which is not yet fully ratified, uses SRFI-132 as it sorting library (scheme sort) which also has list-stable-sort which is the same as the R6RS list-sort .

In Racket you can mix and match libraries from all the languages it supports, but it does not work for lists that are implemented differently and it is a lock in. Being dependent on a different languages library means you cannot run the code with other implementations, like Ikarus and Chez.