mac (01/22/83)
; The following is a LISP macro which can be used to construct circular
; and otherwise tangled list structures, without a lot of rplacas &
; replacds. It's somewhat like the LET REC of ISWIM.
;
; Such a construct is described in Morris & Schwarz, "Computing Cyclic
; List Structures", in the 1980 LISP conference.
; It has the restriction that the results must be cons cells, not atoms.
;
; This construct is more useful in SCHEME, where it can replace the LABELS
; construct for defining (mutually) recursive functions. It's convenient
; in that it's not restricted to defining lambda expressions.
;
; e.g.
(fix ((x (cons 'atom x))) x) ; constructs a circular list of 'atom
(fix ((loop (list 'cond ; constructs a loop
'(done result)
(list 't
'(do-something)
loop
) ) )
(fun (list 'lambda () loop))
)
(fun) ; ... and executes it
)
; (macro source in net.sources)