(Nils' Scheme Snippets)

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(substitute form alist) => form

Purpose

Substitute subforms of a given form. The association list alist contains the forms to be substituted as keys and the substitutes as values.

Arguments

form	source form
alist	substitutions

Example

(substitute '(* (+ 5 7) 9) '(((+ 5 7) . 12)))
=> (* 12 9)

(define (substitute x a)
  (cond ((assoc x a) => cdr)
        ((pair? x)
          (cons (substitute (car x) a)
                (substitute (cdr x) a)))
        (else x)))