You can associate arbitrary properties with any procedure. Each property is a (key, value)-pair. Usually the key is a symbol, but it can be any object.
The system uses certain internal properties:
'name refers to the name used when a procedure is printed;
'emacs-interactive is used to implement Emacs
'setter is used to associate a
Get the property value corresponding to the given key.
If proc has no property with the given key,
return default (which defaults to
Associate the given value with the key property of proc.
To change the print name of the standard
+ procedure (probably
not a good idea!), you could do:
(set-procedure-property! + 'name 'PLUS)
Note this only changes the name property used for printing:
+ ⇒ #<procedure PLUS> (+ 2 3) ⇒ 5 (PLUS 3 4) ⇒ ERROR
As a matter of style, it is cleaner to use the
form, as it is a more declarative interface.
Defines name as a compound procedure consisting of the specified methods, with the associated properties. Applying name select the "best" method, and applies that. See the following section on generic procedures.
For example, the standard
vector-ref procedure specifies
one method, as well as the
(define-procedure vector-ref setter: vector-set! (lambda (vector::vector k ::int) (invoke vector 'get k)))
You can also specify properties in the lambda body:
(define (vector-ref vector::vector k ::int) setter: vector-set! (invoke vector 'get k))
The name of a procedure (as a symbol), which is used when the procedure is printed.
Set the setter procedure associated with the procedure.
Used during the validation phase of the compiler.
Used during the bytecode-generation phase of the compiler: If we see a call to a known function with this property, we can emit custom bytecode for the call.