Module (chicken memory representation)
The procedures from this module operate on the in-memory representation of Scheme objects. These procedures are safe, so, for example, unlike the procedures from (chicken memory) these procedures will type-check and range-check their arguments, but you still need to know what you're doing because the effects may be surprising for the uninitiated.
Extending procedures with data
extend-procedure
[procedure] (extend-procedure PROCEDURE X)Returns a copy of the procedure PROCEDURE which contains an additional data slot initialized to X. If PROCEDURE is already an extended procedure, then its data slot is changed to contain X and the same procedure is returned. Signals an error when PROCEDURE is not a procedure.
extended-procedure?
[procedure] (extended-procedure? PROCEDURE)Returns #t if PROCEDURE is an extended procedure, or #f otherwise.
procedure-data
[procedure] (procedure-data PROCEDURE)Returns the data object contained in the extended procedure PROCEDURE, or #f if it is not an extended procedure.
set-procedure-data!
[procedure] (set-procedure-data! PROCEDURE X)Changes the data object contained in the extended procedure PROCEDURE to X. Signals an error when PROCEDURE is not an extended procedure.
(define foo (letrec ((f (lambda () (procedure-data x))) (x #f) ) (set! x (extend-procedure f 123)) x) ) (foo) ==> 123 (set-procedure-data! foo 'hello) (foo) ==> hello
Low-level data access
These procedures operate with what are known as vector-like objects. A vector-like object is a vector, record structure, pair, symbol or keyword: it is an aggregation of other Scheme objects.
Note that strings and bytevectors are not considered vector-like (they are considered to be byte vectors, which are objects of mostly unstructured binary data).
vector-like?
[procedure] (vector-like? X)Returns #t when X is a vector-like object, returns #f otherwise.
block-ref
[procedure] (block-ref VECTOR* INDEX)Returns the contents of the INDEXth slot of the vector-like object VECTOR*.
block-set!
[procedure] (block-set! VECTOR* INDEX X)[procedure] (set! (block-ref VECTOR* INDEX) X)
Sets the contents of the INDEXth slot of the vector-like object VECTOR* to the value of X.
number-of-slots
[procedure] (number-of-slots VECTOR*)Returns the number of slots that the vector-like object VECTOR* contains.
number-of-bytes
[procedure] (number-of-bytes BLOCK)Returns the number of bytes that the object BLOCK holds. BLOCK may be any non-immediate value. For strings and symbols, the size of the buffer holding the encoded characters is returned.
object-copy
[procedure] (object-copy X)Copies X recursively and returns the fresh copy. Objects allocated in static memory are copied back into garbage collected storage.
Record instance
make-record-instance
[procedure] (make-record-instance SYMBOL ARG1 ...)Returns a new instance of the record type SYMBOL, with its slots initialized to ARG1 .... To illustrate:
(define-record-type point (make-point x y) point?
(x point-x point-x-set!)
(y point-y point-y-set!))
expands into something quite similar to:
(begin
(define (make-point x y)
(make-record-instance 'point x y) )
(define (point? x)
(and (record-instance? x)
(eq? 'point (block-ref x 0)) ) )
(define (point-x p) (block-ref p 1))
(define (point-x-set! p x) (block-set! p 1 x))
(define (point-y p) (block-ref p 2))
(define (point-y-set! p y) (block-set! p 1 y)) )
record-instance?
[procedure] (record-instance? X [SYMBOL])Returns #t if X is a record structure, or #f otherwise.
Further, returns #t if X is of type SYMBOL, or #f otherwise.
record-instance-type
[procedure] (record-instance-type RECORD)Returns type symbol of the record structure RECORD. Signals an error if RECORD is not a record structure.
record-instance-length
[procedure] (record-instance-length RECORD)Returns number of slots for the record structure RECORD. The record-instance type is not counted. Signals an error if RECORD is not a record structure.
record-instance-slot
[procedure] (record-instance-slot RECORD INDEX)Returns the contents of the INDEXth slot of the record structure RECORD. The slot index range is the open interval [0 record-instance-length). Signals an error if RECORD is not a record structure.
record-instance-slot-set!
[procedure] (record-instance-slot-set! RECORD INDEX X)[procedure] (set! (record-instance-slot RECORD INDEX) X)
Sets the INDEXth slot of the record structure RECORD to X. The slot index range is the open interval [0 record-instance-length). Signals an error if RECORD is not a record structure.
record->vector
[procedure] (record->vector RECORD)Returns a new vector with the type and the elements of the record structure RECORD. Signals an error if RECORD is not a record structure.
Magic
object-become!
[procedure] (object-become! ALIST)Changes the identity of the value of the car of each pair in ALIST to the value of the cdr. Neither value may be immediate (i.e. exact integers, characters, booleans or the empty list).
(define x "i used to be a string") (define y '#(and now i am a vector)) (object-become! (list (cons x y))) x ==> #(and now i am a vector) y ==> #(and now i am a vector) (eq? x y) ==> #t
Note: this operation invokes a major garbage collection.
The effect of using object-become! on evicted data (see object-evict) is undefined.
mutate-procedure!
[procedure] (mutate-procedure! OLD PROC)Replaces the procedure OLD with the result of calling the one-argument procedure PROC. PROC will receive a copy of OLD that will be identical in behaviour to the result of OLD:
;;; Replace arbitrary procedure with tracing one: (mutate-procedure! my-proc (lambda (new) (lambda args (printf "~s called with arguments: ~s~%" new args) (apply new args) ) ) )
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