5.26  Unit: tinyclos

This unit is a port of Gregor Kiczales TinyCLOS with numerous modifications.

This unit uses the extras unit.

5.26.1  Defining forms

[syntax] (define-class NAME (SUPERCLASS1 ...) (SLOTNAME1 ...) [METACLASS])
Sets the variable NAME to a new class (a new instance of the class <class>). SUPERCLASS1 ... is a list of superclasses of the newly created class. If no superclasses are given, then <object> is assumed. SLOTNAME1 ... are the names of the direct slots of the class. if METACLASS is provided, then the new class-instance is an instance of METACLASS instead of <class>.

(define-class NAME (SUPER) (SLOT1 SLOT2) META)

is equivalent to

(define NAME
  (make META 
    'name 'NAME
    'direct-supers (list SUPER)
    'direct-slots (list 'SLOT1 'SLOT2)) )

Note that slots-names are not required to be symbols, so the following is perfectly valid:

(define hidden-slot (list 'hidden))
(define <myclass>
  (make <class>
     'direct-supers (list <object>)
     'direct-slots (list hidden-slot) ) )
(define x1 (make <myclass>)
(slot-set! x1 hidden-slot 99)

[syntax] (define-generic NAME)
Sets the variable NAME to contain a fresh generic function object without associated methods.

[syntax] (define-method (NAME (VARIABLE1 CLASS1) ... PARAMETERS ...) BODY ...)
Adds a new method with the code BODY ... to the generic function that was assigned to the variable name. CLASS1 ... is a list if classes that specialize this particular method. The method can have additional parameters PARAMETERS, which do not specialize the method any further. Inside the body of the method the identifier call-next-method names a procedure of zero arguments that can be invoked to call the next applicable method with the same arguments. If no generic function is defined under this name, then a fresh generic function object is created and assigned to NAME.

5.26.2  Base language

[procedure] (add-method GENERIC METHOD)
Adds the method object METHOD to the list of applicable methods for the generic function GENERIC.

[procedure] (instance? X)
Returns #t if X is an instance of a non-primitive class.

[procedure] (make CLASS INITARG ...)
Creates a new instance of CLASS and passes INITARG ... to the initialize method of this class.

[procedure] (make-class SUPERCLASSES SLOTNAMES)
Creates a new class object, where SUPERCLASSES should be the list of direct superclass objects and SLOTNAMES should be a list of symbols naming the slots of this class.

[procedure] (make-generic [NAME])
Creates a new generic function object. If NAME is specified, then it should be a string.

[procedure] (make-method SPECIALIZERS PROC)
Creates a new method object specialized to the list of classes in SPECIALIZERS.

(define-method (foo (<bar> x)) 123)
   <=> (add-method foo (make-method (list <bar>) (lambda (call-next-method x) 123)))

[procedure] (slot-ref INSTANCE SLOTNAME)
Returns the value of the slot SLOTNAME of the object INSTANCE.

[procedure] (slot-set! INSTANCE SLOTNAME VALUE)
Sets the value of the slot SLOTNAME of the object INSTANCE to VALUE.

5.26.3  Introspection

[procedure] (class-cpl CLASS)
Returns the class-precedence-list of CLASS as a list of classes.

[procedure] (class-direct-slots CLASS)
Returns the list of direct slots of CLASS as a list of lists, where each sublist contains the name of the slot.

[procedure] (class-direct-supers CLASS)
Returns the list of direct superclasses of CLASS.

[procedure] (class-of X)
Returns the class that the object X is an instance of.

[procedure] (class-name CLASS)
Returns name of CLASS.

[procedure] (class-slots CLASS)
Returns the list of all slots of CLASS and its superclasses as a list of lists, where each sublist contains the name of the slot.

[procedure] (generic-methods GENERIC)
Returns the list of all methods associated with the generic function GENERIC.

[procedure] (method-specializers METHOD)
Returns the list of classes that specialize METHOD.

[procedure] (method-procedure METHOD)
Returns the procedure that contains the body of METHOD.

[procedure] (subclass? CLASS1 CLASS2)
Returns #t is CLASS1 is a subclass of CLASS2, or #f otherwise. Note that the following holds:

(subclass? X X) ==> #t

5.26.4  Intercessory protocol

[generic] (allocate-instance CLASS)
Allocates storage for an instance of CLASS and returns the instance.

[generic] (compute-apply-generic GENERIC)
[generic] (compute-apply-methods GENERIC)
[generic] (compute-methods GENERIC)
These are used to compute the actual methods to be called on the invocation of the generic function GENERIC.

[generic] (compute-cpl CLASS)
Computes and returns the class-precedence-list of CLASS.

[generic] (compute-getter-and-setter CLASS SLOT ALLOCATOR)
Returns two values, the procedures that get and set the contents of the slot SLOT. ALLOCATOR is a procedure of one argument (I currently don't know what it does).

[generic] (compute-method-more-specific? GENERIC)
Returns a procedure of three arguments (two methods and a list of arguments) that returns #t if the first method is more specific than the second one with respect to the list of arguments. Otherwise the returned predicate returns #f.

[generic] (compute-slots CLASS)
Computes and returns the list of slots of CLASS.

[generic] (initialize INSTANCE INITARGS)
Initializes the object INSTANCE. INITARGS is the list of initialization arguments that were passed to the make procedure.

5.26.5  Additional protocol

[generic] (describe-object INSTANCE PORT)
Writes a description of INSTANCE to PORT. Execution of the interpreter command ,d will invoke this generic function.

[generic] (print-object INSTANCE PORT)
Writes a textual representation of INSTANCE to PORT. Any output of an instance with display, write and print will invoke this generic function.

5.26.6  Utility procedures

[procedure] (initialize-slots INSTANCE INITARGS)
This procedure takes a sequence of alternating slot-names and initialization values in INITARGS and initializes the corresponding slots in INSTANCE.

(define-class <pos> () (x y))

(define-method (initialize (<pos> pos) initargs)
  (call-next-method)
  (initialize-slots pos initargs))

(define p1 (make <pos> 'x 1 'y 2))
(define p2 (make <pos> 'x 3 'y 5))

5.26.7  Builtin classes

The class hierarchy of builtin classes looks like this:

<top>
  <object>
    <class>
      <procedure-class>
        <procedure>
        <entity-class>
          <generic>
      <primitive-class>
  <primitive>
    <void>
    <boolean>
    <symbol>
    <char>
    <vector>
    <pair>
    <number>
      <exact>
      <inexact>
    <string>
    <port>
      <input-port>
      <output-port>
    <pointer>
      <tagged-pointer>
    <locative>
    <byte-vector>
      <u8vector>
      <s8vector>
      <u16vector>
      <s16vector>
      <u32vector>
      <s32vector>
      <f32vector>
      <f64vector>
    <structure>
      <array>
      <char-set>
      <condition>
      <environment>
      <hash-table>
      <lock>
      <mmap>
      <promise>
      <queue>
      <tcp-listener>
      <time>
    <end-of-file>

[class] <primitive> -> <top>
The parent class of the classes of all primitive Scheme objects.

[class] <boolean> -> <primitive>
[class] <symbol> -> <primitive>
[class] <char> -> <primitive>
[class] <vector> -> <primitive>
[class] <null> -> <primitive>
[class] <pair> -> <primitive>
[class] <number> -> <primitive>
[class] <exact> -> <number>
[class] <inexact> -> <number>
[class] <string> -> <primitive>
[class] <port> -> <primitive>
[class] <environment> -> <structure>
[class] <end-of-file> -> <primitive>
[class] <input-port> -> <port>
[class] <output-port> -> <port>
[class] <procedure> -> <procedure-class>
The classes of primitive Scheme objects.

[class] <byte-vector> -> <primitive>
[class] <structure> -> <primitive>
[class] <hash-table> -> <structure>
[class] <queue> -> <structure>
The classes of extended data types provided by the various library units.

[class] <class> -> <object>
The parent class of all class objects.

[class] <entity-class> -> <class>
The parent class of objects that can be invoked as a procedure and have slots.

[class] <generic> -> <entity-class>
The parent class of generic function objects.

[class] <method> -> <class>
The parent class of method objects.

[class] <object> -> <class>
The parent class of all objects.

[class] <procedure-class> -> <class>
The parent class of objects that can be invoked as a procedure.

[class] <condition> -> <structure>
Class of condition objects.

[class] <array> -> <structure>
[class] <char-set> -> <structure>
[class] <time> -> <structure>
[class] <u8vector> -> <byte-vector>
[class] <s8vector> -> <byte-vector>
[class] <u16vector> -> <byte-vector>
[class] <s16vector> -> <byte-vector>
[class] <u32vector> -> <byte-vector>
[class] <s32vector> -> <byte-vector>
[class] <f32vector> -> <byte-vector>
[class] <f64vector> -> <byte-vector>
The classes of data objects provided by the various supported SRFIs.

[class] <lock> -> <structure>
[class] <mmap> -> <structure>
Classes of objects used in the posix library unit.

[class] <pointer> -> <primitive>
[class] <tagged-pointer> -> <pointer>
A machine pointer (untagged, or tagged).

[class] <locative> -> <primitive>
A locative.

[class] <promise> -> <structure>
The class of objects returned by delay.

[class] <tcp-listener> -> <structure>
The class of an object returned by tcp-listen.