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|
#| Copyright (C) 2025 Peter McGoron
|
| Permission is hereby granted, free of charge, to any person obtaining a
| copy of this software and associated documentation files (the
| "Software"), to deal in the Software without restriction, including
| without limitation the rights to use, copy, modify, merge, publish,
| distribute, sublicense, and/or sell copies of the Software, and to
| permit persons to whom the Software is furnished to do so, subject to
| the following conditions:
|
| The above copyright notice and this permission notice (including the
| next paragraph) shall be included in all copies or substantial portions
| of the Software.
|
| THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
| OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
| MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
| IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
| CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
| TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
| SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
|#
;;; This is the low-level Chicken code that implements tagged procedures.
;;; The standard `extend-procedure` cannot be used because it is mutating
;;; by default, while SRFI-259 is persistent.
;;;
;;; The code works by having a "signifier pair", whose car is a unique
;;; (in the sense of eqv) symbol and whose cdr is a integer map to the
;;; tag values.
;;;
;;; The code is similar to `extend-procedure`.
(define unique-id
;; Generate a fixnum, which will serve as the ID for each tagged
;; procedure constructor.
(let ((i 0))
(lambda ()
(set! i (fx+ i 1))
i)))
(define unique-symbol
;; This uninterned symbol is guaranteed to be a unique memory location
;; and is used to pick out the procedure tag mapping from the closure
;; data.
(string->uninterned-symbol "srfi-259"))
(define create/signifier-pair
;; Given a procedure that does not have tags associated with it, create
;; a new procedure object, with the same underlying procedure and closed
;; over variables, with `sig` as the signifier pair.
(foreign-primitive scheme-object ((scheme-object proc)
(scheme-object sig))
"
int old_size = C_header_size(proc);
C_word closure[C_SIZEOF_CLOSURE(old_size + 1)];
int i;
closure[0] = C_CLOSURE_TYPE | (old_size + 1);
for (i = 0; i < old_size; i++)
C_block_item(closure, i) = C_block_item(proc, i);
// C_mutate_slot(&C_block_item(closure, i), C_block_item(proc, i));
C_block_item(closure, old_size) = sig;
C_return(closure);"))
(define set-signifier-pair
;; Given a procedure that has tags associated with it, create a new
;; procedure object, with the same underlying procedure and closure,
;; with `sig` as the signifier pair.
(foreign-primitive scheme-object ((scheme-object proc)
(scheme-object unique_symbol)
(scheme-object sig))
"
int size = C_header_size(proc);
C_word item;
int i;
C_word closure[C_SIZEOF_CLOSURE(size)];
closure[0] = C_CLOSURE_TYPE | size;
for (i = 0; i < size; i++) {
item = C_block_item(proc, i);
if (!C_immediatep(item) && C_pairp(item) && C_eqp(unique_symbol, C_u_i_car(item))) {
C_block_item(closure, i) = sig;
// C_mutate_slot(&C_block_item(closure, i), sig);
} else {
C_block_item(closure, i) = item;
// C_mutate_slot(&C_block_item(closure, i), C_block_item(proc, i));
}
}
C_return(closure);
"))
(define (decoration-is-tag? x)
;; Return true if a decoration is a tagged procedure.
(and (pair? x)
(eq? (car x) unique-symbol)))
(define (get-mapping proc)
;; Return the mapping in a tagged procedure if it exists, or `#f` if it
;; does not exist. This relies on an undocumented internal function,
;; although it could be implemented with documented functions.
(cond
((not (procedure? proc)) (abort
(make-property-condition 'type
'message
"not a procedure")))
((##sys#lambda-decoration proc decoration-is-tag?) => cdr)
(else #f)))
(define (make-signifier fxmap)
;; Create a signifier pair that can be inserted into the closure.
(cons unique-symbol fxmap))
(define (set-tagged-mapping proc key value)
;; Return a new closure object that is tagged, has all of its previous
;; tags except that `key` maps to `value`.
(cond
((get-mapping proc)
=> (lambda (oldmap)
(set-signifier-pair proc
unique-symbol
(make-signifier
(fxmapping-set oldmap key value)))))
;; get-mapping will test if `proc` is a procedure
(else (create/signifier-pair proc (make-signifier
(fxmapping key value))))))
|
