SRFI-31 - A special form ‘rec’ for recursive evaluation ​

SRFI-31 defines a special form that can be used to create self-referential expressions more conveniently. The syntax is as follows:

lisp
<rec expression> --> (rec <variable> <expression>)
<rec expression> --> (rec (<variable>+) <body>)

The first syntax can be used to create self-referential expressions, for example:

lisp
  guile> (define tmp (rec ones (cons 1 (delay ones))))

The second syntax can be used to create anonymous recursive functions:

lisp
  guile> (define tmp (rec (display-n item n)
                       (when (positive? n)
                         (display item) (newline)
                         (display-n item (- n 1)))))
  guile> (tmp 42 3)
  42
  42
  42
  guile>