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; Copyright (c) 1993-1999 by Richard Kelsey and Jonathan Rees. See file COPYING.
;;;; Records
; Every record in the image is assumed to be made either by MAKE-RECORD-TYPE
; or by a procedure returned by record-constructor. A record-type is a
; record that describes a type of record. At the end of the file we create
; a record type that describes record types.
; Every record has a record type (another record) in the first slot.
(define (record-type r)
(record-ref r 0))
; We number the record types for debugging purposes.
(define *record-type-uid* -1)
; This is the record type that describes record types. It is set a the end
; of the file. Its first slot points to itself.
(define *record-type* #f)
; Make a record type from a name, used for printing and debugging, and
; a list of field names.
;
; The VM references both the record type and the resumer, so their offsets
; should not be changed.
(define (make-record-type name field-names)
(set! *record-type-uid* (+ *record-type-uid* 1))
(let ((r (make-record 7 (unspecific))))
(record-set! r 0 *record-type*)
(record-set! r 1 default-record-resumer)
(record-set! r 2 *record-type-uid*)
(record-set! r 3 name)
(record-set! r 4 field-names)
(record-set! r 5 (length field-names))
(record-set! r 6 (make-default-record-discloser name))
r))
(define (record-type? obj)
(and (record? obj)
(eq? (record-type obj) *record-type*)))
; The various fields in a record type.
(define (record-type-resumer rt) (record-ref rt 1))
(define (set-record-type-resumer! rt r) (record-set! rt 1 r))
(define (record-type-uid rt) (record-ref rt 2))
(define (record-type-name rt) (record-ref rt 3))
(define (record-type-field-names rt) (record-ref rt 4))
(define (record-type-number-of-fields rt) (record-ref rt 5))
(define (record-type-discloser rt) (record-ref rt 6))
(define (set-record-type-discloser! rt d) (record-set! rt 6 d))
; This is a hack; it is read by the script that makes c/scheme48.h.
(define record-type-fields
'(resumer uid name field-names number-of-fields discloser))
;----------------
; Given a record type and the name of a field, return the field's index.
(define (record-field-index rt name)
(let loop ((names (record-type-field-names rt))
(i 1))
(cond ((null? names)
(error "unknown field"
(record-type-name rt)
name))
((eq? name (car names))
i)
(else
(loop (cdr names) (+ i 1))))))
; Return procedure for contstruction records of type RT. NAMES is a list of
; field names which the constructor will take as arguments. Other fields are
; uninitialized.
(define (record-constructor rt names)
(let ((indexes (map (lambda (name)
(record-field-index rt name))
names))
(size (+ 1 (record-type-number-of-fields rt))))
(lambda args
(let ((r (make-record size (unspecific))))
(record-set! r 0 rt)
(let loop ((is indexes) (as args))
(if (null? as)
(if (null? is)
r
(error "too few arguments to record constructor"
rt names args))
(if (null? is)
(error "too many arguments to record constructor"
rt names args)
(begin (record-set! r (car is) (car as))
(loop (cdr is) (cdr as))))))))))
; Making accessors, modifiers, and predicates for record types.
(define (record-accessor rt name)
(let ((index (record-field-index rt name))
(error-cruft `(record-accessor ,rt ',name)))
(lambda (r)
(if (eq? (record-type r) rt)
(record-ref r index)
(call-error "invalid record access" error-cruft r)))))
(define (record-modifier rt name)
(let ((index (record-field-index rt name))
(error-cruft `(record-modifier ,rt ',name)))
(lambda (r x)
(if (eq? (record-type r) rt)
(record-set! r index x)
(call-error "invalid record modification" error-cruft r x)))))
(define (record-predicate rt)
(lambda (x)
(and (record? x)
(eq? (record-type x) rt))))
;----------------
; A discloser is a procedure that takes a record of a particular type and
; returns a list whose head is a string or symbol and whose tail is other
; stuff.
;
; Set the discloser for record type RT.
(define (define-record-discloser rt proc)
(if (and (record-type? rt)
(procedure? proc))
(set-record-type-discloser! rt proc)
(call-error "invalid argument" define-record-discloser rt proc)))
; By default we just return the name of the record type.
(define (make-default-record-discloser record-type-name)
(lambda (r)
(list record-type-name)))
; DISCLOSE-RECORD calls the record's discloser procedure to obtain a list.
(define (disclose-record r)
(if (record? r)
(let ((rt (record-type r)))
(if (record-type? rt)
((record-type-discloser rt) r)
#f))
#f))
;----------------
; A resumer is a procedure that the VM calls on all records of a given
; type on startup.
;
; A resumer may be:
; #t -> do nothing on startup.
; #f -> records of this type do not survive a dump/resume; in images they
; are replaced by their first slot (so we make sure they have one)
; a one-argument procedure -> pass the record to this procedure
;
; Resumers are primarily intended for use by external code which keeps
; fields in records which do not survive a dump under their own power.
; For example, a record may contain a reference to a OS-dependent value.
;
; Resumers are called by the VM on startup.
(define (define-record-resumer rt resumer)
(if (and (record-type? rt)
(or (eq? #t resumer)
(and (eq? #f resumer)
(< 0 (record-type-number-of-fields rt)))
(procedure? resumer)))
(set-record-type-resumer! rt resumer)
(call-error "invalid argument" define-record-resumer rt resumer)))
; By default we leave records alone.
(define default-record-resumer
#t)
(define (initialize-records! resumer-records)
(if (vector? resumer-records)
(do ((i 0 (+ i 1)))
((= i (vector-length resumer-records)))
(resume-record (vector-ref resumer-records i)))))
(define (resume-record record)
((record-type-resumer (record-type record))
record))
;----------------
; Initializing *RECORD-TYPE* and making a type.
(set! *record-type*
(make-record-type 'record-type record-type-fields))
(record-set! *record-type* 0 *record-type*)
(define :record-type *record-type*)
(define-record-discloser :record-type
(lambda (rt)
(list 'record-type
(record-type-uid rt)
(record-type-name rt))))
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