R5RS circular dependency (cycle in loading)-CodePudding

I have two r5rs files - scheme-interpreter.scm and scheme-interpreter-operations.scm. The first file contains two functions - interpret and evaluate. The second file contains auxilliary functions, which get called inside evaluate. However, these functions can call evaluate as well. Thus, recursion occurs. When I reference each file in the other one like this:

scheme-interpreter.scm:

(#%require "scheme-interpreter-operations.scm")
(#%provide (all-defined))

scheme-interpreter-operations.scm:

#lang r5rs
(#%require "scheme-interpreter-operations.scm")
(#%provide (all-defined))

I get errors. Is it possible to load files in a circular manner?

CodePudding user response：

Using the Racket R5RS language with the racket module system on top like in your sample code, it's possible to have circular dependencies using using lazy-require.

Example:

s1.scm:

#lang r5rs

(#%require "s2.scm")
(#%provide (all-defined))

(define (evaluate x)
  (cond
   ((and (pair? x) (eq? (car x) ' ))
    (add (cdr x)))
   ((number? x) x)))

(display (evaluate '(  1 2)))
(newline)

s2.scm:

#lang r5rs

(#%require racket/lazy-require)
(lazy-require ("s1.scm" (evaluate))) ; Lazily import evaluate
(#%provide (all-defined))

(define (add x)
  (apply   (map evaluate x)))

And demonstration:

$ racket s1.scm
3

For a general R5RS approach, a (load "s2.scm") in s1.scm works with Chicken, Guile and plt-r5rs, at least (With the Racket specific stuff removed, of course). Adjust filenames appropriately.