;;; srfi-31.scm --- special form for recursive evaluation

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(define-module (srfi srfi-31)
  :export-syntax (rec))

(define-macro (rec arg-form . body)
  (cond
   ((and (symbol? arg-form) (= 1 (length body)))
    ;; (rec S (cons 1 (delay S)))
    `(letrec ((,arg-form ,(car body)))
       ,arg-form))
   ;; (rec (f x) (+ x 1))
   ((list? arg-form)
    `(letrec ((,(car arg-form) (lambda ,(cdr arg-form) ,@body)))
       ,(car arg-form)))
   (else
    (error "syntax error in rec form" `(rec ,arg-form ,@body)))))