optima

alexandria

closer-mop

optima is a fast pattern matching library which
uses optimizing techniques widely used in the functional programming
world. See the following references for more details:

* [Optimizing Pattern Matching](http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.6.5507) by Fabrice Le Fessant, Luc Maranget
* [The Implementation of Functional Programming Languages](http://research.microsoft.com/en-us/um/people/simonpj/papers/slpj-book-1987/) by Simon Peyton Jones

Pattern Language
----------------

A pattern specifier, or a pattern for short ambiguous, is an
expression that describes how a value matches some
specification. Pattern specifiers are defined as follows:

    pattern-specifier ::= constant-pattern
                        | variable-pattern
                        | place-pattern
                        | guard-pattern
                        | not-pattern
                        | or-pattern
                        | and-pattern
                        | constructor-pattern
                        | derived-pattern
    constant-pattern ::= t | nil
                       | keyword
                       | atom-except-symbol
                       | (quote VALUE)
    variable-pattern ::= SYMBOL | (variable SYMBOL)
    place-pattern ::= (place SYMBOL)
    guard-pattern ::= (guard PATTERN TEST-FORM)
    not-pattern ::= (not PATTERN)
    or-pattern ::= (or PATTERN*)
    and-pattern ::= (and PATTERN*)
    constructor-pattern ::= (NAME ARG*)
    derived-pattern ::= (NAME PATTERN*)

### Constant-Pattern

A constant-pattern matches the constant itself.

Examples:

    (match 1 (1 2)) => 2
    (match "foo" ("foo" "bar")) => "bar"
    (match '(1) ('(1) 2)) => 2

### Variable-Pattern

A variable-pattern matches any value and binds the value to the
variable. "_" and "otherwise" are special variable-patterns (a.k.a
wildcard-pattern) which match any value but don't bind.

Examples:

    (match 1 (x x)) => 1
    (match 1 (_ 2)) => 2
    (match 1
      (2 2)
      (otherwise 'otherwise))
    => OTHERWISE

### Place-Pattern

A place-pattern matches any value, in the same way as
variable-patterns do, but binds the value by using SYMBOL-MACROLET.

Examples:

    (defvar c (cons 1 2))
    (match c ((cons (place x) y) (incf x) (incf y)))
    c
     => (2 . 2)

### Guard-Pattern

A guard-pattern is a special pattern that tests whether TEST-FORM is
satisfied in the current matching context.

Examples:

    (match 1 ((guard x (eql x 2)) t))
    => NIL
    (match 1 ((guard x (eql x 1)) t))
    => T

### Not-Pattern

A not-pattern matches a value that is not matched with sub-PATTERN.

Examples:

    (match 1 ((not 2) 3)) => 3
    (match 1 ((not (not 1)) 1)) => 1

### Or-Pattern

An or-pattern matches a value that is matched with one of
sub-PATTERNs.

Examples:

    (match '(2 . 1) ((or (cons 1 x) (cons 2 x)) x))
    => 1

### And-Pattern

An and-pattern matches a value that is matched with all of its
sub-PATTERNs. The most common use case is to match a value and bind
the value to a variable.

Examples:

    (match 1 ((and 1 x) x))
    => 1

### Constructor-Pattern

A constructor-pattern matches the sub-components of a value based on
its structure. The following constructors are available:

#### CONS

Syntax:

    cons-constructor-pattern ::= (cons CAR-PATTERN CDR-PATTERN)

Examples:

    (match '(1 . 2)
      ((cons a b) (+ a b)))
     => 3

#### ASSOC

Syntax:

    assoc-constructor-pattern ::= (assoc ITEM PATTERN &key key test)

Examples:

    (match '((1 . :one))
      ((assoc 1 x) x))
    => :ONE
    (match '((1 . :one) (2 . :two))
      ((assoc 2 x) x))
    => :TWO
    (match '(1 (2 . 3))
      ((assoc 2 x) x))
    => 3
    (match '(("a" . 123))
      ((assoc "A" 123 :test #'string-equal) t))
    => T

#### PROPERTY

Syntax:

    property-constructor-pattern ::= (property KEY PATTERN)

Examples:

    (match '(:a 1)
      ((property :a x) x))
    => 1
    (match '(:a 1 :b 2)
      ((property :b x) x))
    => 2
    (match '(:a 1 2)
      ((property :a x) x))
    => 1

#### VECTOR

Syntax:

    vector-constructor-pattern ::= (vector PATTERN*)

Examples:

    (match #(1 2)
      ((vector a b) (+ a b)))
    => 3

#### SIMPLE-VECTOR

Syntax:

    simple-vector-constructor-pattern ::= (simple-vector PATTERN*)

Examples:

    (match #(1 2)
      ((simple-vector a b) (+ a b)))
    => 3

#### CLASS

Matches an instance of a given subclass of standard-class, as well as
the instance's slots.

Syntax:

    class-constructor-pattern ::= (class NAME slot*)
                                | (NAME slot*)
    slot ::= SLOT-NAME
           | (SLOT-NAME PATTERN*)

CLASS can be omitted. If slot is a symbol, then it will be regarded
as (slot slot). If more than one PATTERN is given, then they will be
wrapped by and-pattern like (and PATTERN*).

Examples:

    (defclass point ()
      ((x :initarg :x)
       (y :initarg :y)))
    (defvar p (make-instance 'point :x 1 :y 2))
    (match p
      ((point x y) (list x y)))
    => (1 2)
    (match p
      ((point (x 1 x)) x))
    => 1
    (defstruct person (name age))
    (defvar foo (make-person :name "foo" :age 30))
    (match foo
      ((person name age) (list name age)))
    => ("foo" 30)

You can also use MAKE-INSTANCE style pattern syntax like:

    (match foo
      ((person :name name :age age) (list name age)))
    => ("foo" 30)

This is equal to the example above except this implicitly resolves the
slot names using the Metaobject Protocol. In this case, you have to
make sure the slot names can be determined uniquely during the
compilation. Otherwise, you will get a compiler error.

#### STRUCTURE

Matches any structure value, and its slot values.

Syntax:

    structure-constructor-pattern ::= (structure CONC-NAME slot*)
                                    | (CONC-NAME slot*)
    slot ::= SLOT-NAME
           | (SLOT-NAME PATTERN*)

As in the CLASS constructor-pattern, STRUCTURE can be
omitted. CONC-NAME is a prefix string of a predicate (CONC-NAME +
"p") and accessors (CONC-NAME + SLOT-NAME). For example, if we have
the following defstruct,

    (defstruct person name age)

the structure constructor-pattern (person- name age) is valid because
PERSON-P, PERSON-NAME and PERSON-AGE are available here. Technically,
we don't need an actual structure definition. If we have the following
code, for instance,

    (defun point-p (p) (consp p))
    (defun point-x (p) (car p))
    (defun point-y (p) (cdr p))

the pattern matching below is valid.

    (match (cons 1 2)
      ((point- x y) (list x y)))
    => (1 2)

Examples:

    (defstruct (person (:conc-name :p-)
                       (:predicate p-p))
      name age)
    (match (make-person :name "foo" :age 30)
      ((p- name age) (list name age)))
    => ("foo" 30)

As in the class constructor-pattern, you can also use MAKE-INSTANCE
style pattern syntax like:

    (match (cons 1 2)
      ((point- :x x :y y) (list x y)))
    => (1 2)

### Derived-Pattern

A derived-pattern is a pattern that is defined with DEFPATTERN. There
are some builtin derived patterns as below:

#### LIST

Expansion of LIST derived patterns:

    (list a b c) => (cons a (cons b (cons c nil)))

#### LIST*

Expansion of LIST* derived patterns:

    (list* a b c) => (cons a (cons b c))

#### SATISFIES

Expansion of SATISFIES derived patterns:

    (satisfies f) => (guard it (f it))

#### EQ, EQL, EQUAL, EQUALP

Expansion of EQ, EQL, EQUAL, EQUALP derived patterns:

    (eq 'foo) => (guard it (eq it 'foo))
    (eql 123) => (guard it (eql it 123))
    (equal '(1 2)) => (guard it (equal it '(1 2)))
    (equalp "foo") => (guard it (equalp it "foo"))

#### TYPE

Expansion of TYPE derived patterns:

    (TYPE type) => (guard it (typep it 'type))

Quasiquotation
--------------

You may want to use a quasiquote in a pattern specifier like:

    (match '(1 2 3 4)
      (`(1 ,x ,@y) (list x y)))

To do so, you need to use a specific quasiquote reader, for example
[fare-quasiquote](http://cliki.net/fare-quasiquote) , loading
fare-quasiquote-optima system, because there is no standard expanded
form for quasiquote expressions.

Define Constructor Patterns
---------------------------

You can define your own constructor patterns by using the
`OPTIMA.CORE` package.  First, define a data structure for the
constructor pattern.

    (defstruct (my-cons-pattern (:include constructor-pattern)
                                (:constructor make-cons-pattern (car-pattern cdr-pattern
                                                                 &aux (subpatterns (list car-pattern
                                                                                         cdr-pattern))))))

Note that you must keep `SUBPATTERNS` of the constructor pattern in
sync so that optima can take care of them.

Second, specify a condition for when the destructor of two constructor
patterns can be shared. This makes it possible to perform some
optimizations.

    (defmethod constructor-pattern-destructor-sharable-p ((x my-cons-pattern) (y my-cons-pattern))
      t)

Third, define a destructor generator for the constructor pattern. The
destructor generator will make a destructor that specifies how to
check the the data (`PREDICATE-FORM`) and how to access the
data (`ACCESSOR-FORMS`).

    (defmethod constructor-pattern-make-destructor ((pattern my-cons-pattern) var)
      (make-destructor :predicate-form `(consp ,var)
                       :accessor-forms (list `(car ,var) `(cdr ,var))))

Finally, define a parser and an unparser for the constructor pattern.

    (defmethod parse-constructor-pattern ((name (eql 'my-cons)) &rest args)
      (apply #'make-my-cons-pattern (mapcar #'parse-pattern args)))
    (defmethod unparse-pattern ((pattern my-cons-pattern))
      `(cons ,(unparse-pattern (my-cons-pattern-car-pattern pattern))
             ,(unparse-pattern (my-cons-pattern-cdr-pattern pattern))))

See the source code for more detail.

optima

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optima

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optima.ppcre

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