term-rewrite-system/trs/utilities.scm

(define-module (trs utilities)
  #:use-module (ice-9 match)
  #:use-module (srfi srfi-11)
  #:export (step-body atomic? iterate qqify))

(define (any/map f l)
  (if (null? l)
      (values #f '())
      (let-values (((p1 v1) (f (car l)))
		   ((p2 v2) (any/map f (cdr l))))
	(values (or p1 p2)
		(cons v1 v2)))))

(define (step-body step s)
  (let-values (((progress tail) (any/map step (cdr s))))
    (values progress (cons (car s) tail))))

(define (iterate step s)
  (let-values (((progress s^) (step s)))
    (if progress
	(iterate step s^)
	s^)))

(define (atomic? s)
  (or (symbol? s) (boolean? s) (number? s)))

(define (qqify xs)
  (define (rec x)
    (cond ((symbol? x)
           (list 'unquote x))
          ((or (boolean? x)
               (number? x))
           x)
          (else
           `(,(car x) . ,(map rec (cdr x))))))
  (list 'quasiquote (rec xs)))