The general-accumulator Reference Manual

This is the general-accumulator Reference Manual, generated automatically by Declt version 4.0 beta 2 "William Riker" on Wed May 15 03:59:51 2024 GMT+0.

Table of Contents


1 Introduction


2 Systems

The main system appears first, followed by any subsystem dependency.


2.1 general-accumulator

A general-purpose, extensible value accumulator

Author

Teemu Likonen <>

License

Creative Commons CC0 (public domain dedication)

Source

general-accumulator.asd.

Child Component

accumulator.lisp (file).


3 Files

Files are sorted by type and then listed depth-first from the systems components trees.


3.1 Lisp


3.1.1 general-accumulator/general-accumulator.asd

Source

general-accumulator.asd.

Parent Component

general-accumulator (system).

ASDF Systems

general-accumulator.


3.1.2 general-accumulator/accumulator.lisp

Source

general-accumulator.asd.

Parent Component

general-accumulator (system).

Packages

general-accumulator.

Public Interface
Internals

4 Packages

Packages are listed by definition order.


4.1 general-accumulator

Source

accumulator.lisp.

Nickname

genacc

Use List

common-lisp.

Public Interface
Internals

5 Definitions

Definitions are sorted by export status, category, package, and then by lexicographic order.


5.1 Public Interface


5.1.1 Macros

Macro: with-accumulator ((name object &rest keyword-arguments) &body body)

Create a local function ‘name‘ for handling an accumulation of type _object_. Execute _body_ forms and return the value of the last form.

This macro uses generic functions to handle the accumulation. There are some built-in methods defined for common use-cases (see below) but user can add more methods and therefore any kind of accumulation is possible.

First a new accumulator object is created with the generic function ‘initialize‘. The _object_ argument (evaluated) and optional _keyword-arguments_ (evaluated) are passed to ‘initialize‘ and it should return an accumulator object that stores the state of the accumulation.

Then a local function ‘name‘ is created for simple accumulation. The function can optionally take one argument which is an object to be accumulated. The generic function ‘accumulate‘ is used to handle the accumulation. The return value of the local function comes from the generic function ‘accumulate‘. The built-in accumulators return the input argument.

If the local function is called without arguments then the generic function ‘value‘ is called. It should return the currently accumulated value.

#### Built-in accumulators

The _object_ argument is used to define the type of accumulation process. There are several built-in types:

* ‘:list‘

Creates a list collector. Each accumulated object is collected to a list. Example:

GENACC> (with-accumulator (collect :list)
(collect 1) (collect 2) (collect 3) (collect))
(1 2 3)

The collecting is done destructively. The applicable ‘accumulate‘ method maintains a pointer to the last cons cell of the list and each time modifies its cdr value to point to a new cons cell.

* [a list]

If _object_ is of type ‘list‘ then new elements are collected at the end. Example:

GENACC> (with-accumulator (collect (list 1 2 3))
(collect 4) (collect 5) (collect))
(1 2 3 4 5)

This is a destructive operation. The cdr value of the last cons cell of the original list is modified and linked to a new cons cell.

* ‘:vector‘

Creates a general vector collector. It creates an adjustable vector with a fill pointer 0 and element type T. New elements are pushed to that vector with ‘cl:vector-push-extend‘ function. Example:

GENACC> (with-accumulator (collect :vector)
(collect "first") (collect "second") (collect))
#("first" "second")

* ‘:string‘

This is similar to ‘:vector‘ but the element type is ‘character‘. The underlying ‘accumulate‘ methods can take a single character or a sequence of characters as the argument. Example:

GENACC> (with-accumulator (collect :string)
(collect #\a)
(collect "bcd")
(collect #(#\e #\f))
(collect ’(#\g #\h #\i)) (collect))
"abcdefghi"

* ‘:bit-vector‘

This is similar to ‘:string‘ but the element type is ‘bit‘. The argument for the accumulator function can a bit or a sequence of bits.

* [a vector]

If _object_ is of type ‘vector‘ which satisfies the test ‘cl:array-has-fill-pointer-p‘ then that vector is appended starting from its current fill pointer.

GENACC> (with-accumulator
(collect (make-array 2 :fill-pointer 2 :adjustable t :initial-contents (vector 1 2))) (collect 3)
(collect 4)
(collect))
#(1 2 3 4)

Note that if the vector is not adjustable then the accumulator may reach vector’s limits and ‘cl:vector-push-extend‘ signals an error.

* [a function]

If _object_ is of type ‘function‘ then the accumulator behaves like the ‘cl:reduce‘ function: all accumulated objects are combined into one by calling the given reducer function. Examples:

GENACC> (with-accumulator (summing #’+)
(summing 5) (summing 7) (summing 11) (summing))
23

GENACC> (with-accumulator (nc #’nconc)
(nc (list 1 2 3))
(nc (list 4 5 6))
(nc (list 7 8 9))
(nc))
(1 2 3 4 5 6 7 8 9)

GENACC> (with-accumulator (early-char (lambda (a b)
(if (char< a b) a b))) (early-char #\o)
(early-char #\b)
(early-char #\s)
(early-char))
#\b

#### Adding a custom accumulator

The whole accumulation process is handled by three generic functions: ‘initialize‘, ‘accumulate‘ and ‘value‘. Writing new methods for those functions allow adding any kind of accumulators. The following example adds an accumulator which calculates the arithmetic mean of accumulated numbers.

First we define a class whose instances will keep the state of the accumulator. In this case we need to store the sum and the count of accumulated numbers so we create slots for them.

(defclass mean-accumulator ()
((sum :initform 0)
(count :initform 0)))

Then we add a method for initializing an instance of the class. The generic function ‘initialize‘ is used for that. It is called with the _object_ argument of ‘with-accumulator‘ macro and with optional _keyword-arguments_. In this example we use an _eql_ specializer for symbol ‘:mean‘. We don’t use any keyword arguments so there’s just empty _&key_ at the end of the lambda list.

(defmethod genacc:initialize ((type (eql :mean)) &key) (make-instance ’mean-accumulator))

Now we create a method for generic function ‘accumulate‘. The function is called with two arguments: (1) the accumulator object created by ‘initialize‘ and (2) the object that is meant to be accumulated. This method specializes on our ‘mean-accumulator‘ class as well as on number class. The number is added to the previous value and the count is increased by one.

(defmethod genacc:accumulate ((object mean-accumulator)
(number number))
(with-slots (sum count) object
(incf sum number)
(incf count 1)))

For returning the accumulated mean value we create a method for the generic function ‘value‘. This method, too, must specialize on the ‘mean-accumulator‘ class. We get the current accumulated mean value by dividing the value of _sum_ slot with the value of _count_ slot.

(defmethod genacc:value ((object mean-accumulator))
(with-slots (sum count) object
(/ sum count)))

Now the custom accumulator is ready and it can be used with the ‘with-accumulator‘ macro. Example:

GENACC> (with-accumulator (mean :mean)
(loop repeat 10 do (mean (random 1000)))
(format t "The mean so far: ~A~%" (mean))
(loop repeat 10 do (mean (random 1000)))
(format t "The final mean: ~A~%" (mean)))
The mean so far: 2512/5
The final mean: 2704/5
NIL

Package

general-accumulator.

Source

accumulator.lisp.


5.1.2 Generic functions

Generic Function: accumulate (accumulator object)

Accumulate _object_ to _accumulator_ instance. Methods of this generic function should specialize at least on the first argument (_accumulator_) and they should accumulate the second argument (_object_) to the accumulator object.

Package

general-accumulator.

Source

accumulator.lisp.

Methods
Method: accumulate ((acc reduce-accumulator) item)
Method: accumulate ((acc list-accumulator) item)
Method: accumulate ((acc special-vector-accumulator) (item cons))
Method: accumulate ((acc special-vector-accumulator) (item vector))
Method: accumulate ((acc vector-accumulator) item)
Method: accumulate :around ((acc accumulator) item)
Generic Function: initialize (object &key &allow-other-keys)

Return an accumulator object which is used to keep the information of an accumulation process.

The _object_ argument can anything and its primary purpose is a method dispatching: different classes of the _object_ establish different kind of accumulators. Methods can use the _object_ value too, as well as any keyword arguments passed to the generic function.

Methods should return an object, usually an instance of some class. That object can later be used with generic functions ‘accumulate‘ and ‘value‘.

Package

general-accumulator.

Source

accumulator.lisp.

Methods
Method: initialize ((function function) &key)
Method: initialize ((object (eql :list)) &key)
Method: initialize ((object list) &key)
Method: initialize ((object (eql :bit-vector)) &key)
Method: initialize ((object (eql :string)) &key)
Method: initialize ((object (eql :vector)) &key)
Method: initialize ((object vector) &key)
Generic Reader: value (accumulator)

Return the accumulated value of _accumulator_ object.

Package

general-accumulator.

Source

accumulator.lisp.

Methods
Reader Method: value ((accumulator accumulator))

automatically generated reader method

Target Slot

value.


5.2 Internals


5.2.1 Classes

Class: accumulator
Package

general-accumulator.

Source

accumulator.lisp.

Direct subclasses
Direct methods
Direct slots
Slot: value
Initargs

:value

Readers

value.

Writers

This slot is read-only.

Class: list-accumulator
Package

general-accumulator.

Source

accumulator.lisp.

Direct superclasses

accumulator.

Direct methods

accumulate.

Direct slots
Slot: last-cons
Initargs

:last-cons

Class: reduce-accumulator
Package

general-accumulator.

Source

accumulator.lisp.

Direct superclasses

accumulator.

Direct methods

accumulate.

Direct slots
Slot: function
Package

common-lisp.

Initargs

:function

Class: special-vector-accumulator
Package

general-accumulator.

Source

accumulator.lisp.

Direct superclasses

vector-accumulator.

Direct methods
Class: vector-accumulator
Package

general-accumulator.

Source

accumulator.lisp.

Direct superclasses

accumulator.

Direct subclasses

special-vector-accumulator.

Direct methods

accumulate.


Appendix A Indexes


A.1 Concepts


A.2 Functions

Jump to:   A   G   I   M   V   W  
Index Entry  Section

A
accumulate: Public generic functions
accumulate: Public generic functions
accumulate: Public generic functions
accumulate: Public generic functions
accumulate: Public generic functions
accumulate: Public generic functions
accumulate: Public generic functions

G
Generic Function, accumulate: Public generic functions
Generic Function, initialize: Public generic functions
Generic Function, value: Public generic functions

I
initialize: Public generic functions
initialize: Public generic functions
initialize: Public generic functions
initialize: Public generic functions
initialize: Public generic functions
initialize: Public generic functions
initialize: Public generic functions
initialize: Public generic functions

M
Macro, with-accumulator: Public macros
Method, accumulate: Public generic functions
Method, accumulate: Public generic functions
Method, accumulate: Public generic functions
Method, accumulate: Public generic functions
Method, accumulate: Public generic functions
Method, accumulate: Public generic functions
Method, initialize: Public generic functions
Method, initialize: Public generic functions
Method, initialize: Public generic functions
Method, initialize: Public generic functions
Method, initialize: Public generic functions
Method, initialize: Public generic functions
Method, initialize: Public generic functions
Method, value: Public generic functions

V
value: Public generic functions
value: Public generic functions

W
with-accumulator: Public macros


A.3 Variables

Jump to:   F   L   S   V  
Index Entry  Section

F
function: Private classes

L
last-cons: Private classes

S
Slot, function: Private classes
Slot, last-cons: Private classes
Slot, value: Private classes

V
value: Private classes