2013-08-11 08:49:33 +00:00
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---
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2013-08-13 17:14:57 +00:00
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language: "Common Lisp"
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2013-08-11 08:49:33 +00:00
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filename: commonlisp.lisp
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contributors:
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- ["Paul Nathan", "https://github.com/pnathan"]
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---
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ANSI Common Lisp is a general purpose, multi-paradigm programming
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language suited for a wide variety of industry applications. It is
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frequently referred to a programmable programming language.
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The classic starting point is [Practical Common Lisp and freely available.](http://www.gigamonkeys.com/book/)
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Another popular and recent book is
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[Land of Lisp](http://landoflisp.com/).
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2013-08-13 15:19:56 +00:00
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```scheme
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2013-08-11 08:49:33 +00:00
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; 0. Syntax
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; General form.
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;; Lisp has two fundamental pieces of syntax: the ATOM and the
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;; S-expression. Typically, grouped S-expressions are called `forms`.
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10 ; an atom; it evaluates to itself
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:THING ;Another atom; evaluating to the symbol :thing.
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t ; another atom, denoting true.
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(+ 1 2 3 4) ; an s-expression
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'(4 :foo t) ;another one
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;;; Comments
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;; Single line comments start with a semicolon; use two for normal
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;; comments, three for section comments, and four for file-level
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;; comments.
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#| Block comments
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can span multiple lines and...
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#|
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they can be nested!
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|#
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|#
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;;; Environment.
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;; A variety of implementations exist; most are
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;; standard-conformant. CLISP is a good starting one.
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;; Libraries are managed through Quicklisp.org's Quicklisp system.
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;; Common Lisp is usually developed with a text editor and a REPL
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;; (Read Evaluate Print Loop) running at the same time. The REPL
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;; allows for interactive exploration of the program as it is "live"
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;; in the system.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; 1. Primitive Datatypes and Operators
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; Symbols
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2013-08-11 17:39:13 +00:00
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'foo ; => FOO Notice that the symbol is upper-cased automatically.
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;; Intern manually creates a symbol from a string.
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(intern "AAAA") ; => AAAA
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2013-08-11 17:39:13 +00:00
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(intern "aaa") ; => |aaa|
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2013-08-11 08:49:33 +00:00
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;;; Numbers
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9999999999999999999999 ; integers
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#b111 ; binary => 7
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#o111 ; octal => 73
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#x111 ; hexadecimal => 273
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3.14159s0 ; single
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3.14159d0 ; double
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1/2 ; ratios
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#C(1 2) ; complex numbers
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;; Function application is written (f x y z ...)
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;; where f is a function and x, y, z, ... are operands
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;; If you want to create a literal list of data, use ' to stop it from
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;; being evaluated - literally, "quote" the data.
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'(+ 1 2) ; => (+ 1 2)
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;; You can also call a function manually:
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(funcall #'+ 1 2 3) ; => 6
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;; Some arithmetic operations
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(+ 1 1) ; => 2
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(- 8 1) ; => 7
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(* 10 2) ; => 20
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(expt 2 3) ; => 8
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(mod 5 2) ; => 1
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(/ 35 5) ; => 7
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(/ 1 3) ; => 1/3
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(+ #C(1 2) #C(6 -4)) ; => #C(7 -2)
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2013-08-11 17:39:13 +00:00
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;;; Booleans
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t ; for true (any not-nil value is true)
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nil ; for false - and the empty list
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(not nil) ; => t
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(and 0 t) ; => t
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(or 0 nil) ; => 0
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;;; Characters
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#\A ; => #\A
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#\λ ; => #\GREEK_SMALL_LETTER_LAMDA
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#\u03BB ; => #\GREEK_SMALL_LETTER_LAMDA
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2013-08-11 17:39:13 +00:00
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;;; Strings are fixed-length arrays of characters.
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2013-08-11 08:49:33 +00:00
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"Hello, world!"
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"Benjamin \"Bugsy\" Siegel" ; backslash is an escaping character
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;; Strings can be concatenated too!
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(concatenate 'string "Hello " "world!") ; => "Hello world!"
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2013-08-11 17:39:13 +00:00
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;; A string can be treated like a sequence of characters
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(elt "Apple" 0) ; => #\A
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;; format can be used to format strings:
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(format nil "~a can be ~a" "strings" "formatted")
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2013-08-11 17:39:13 +00:00
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;; Printing is pretty easy; ~% is the format specifier for newline.
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(format t "Common Lisp is groovy. Dude.~%")
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2013-08-11 08:49:33 +00:00
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; 2. Variables
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; You can create a global (dynamically scoped) using defparameter
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;; a variable name can use any character except: ()[]{}",'`;#|\
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;; Dynamically scoped variables should have earmuffs in their name!
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2013-08-11 08:49:33 +00:00
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(defparameter *some-var* 5)
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*some-var* ; => 5
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2013-08-11 17:39:13 +00:00
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;; You can also use unicode characters.
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(defparameter *AΛB* nil)
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2013-08-11 17:39:13 +00:00
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;; Accessing a previously unbound variable is an
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;; undefined behavior (but possible). Don't do it.
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2013-08-11 08:49:33 +00:00
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;; Local binding: `me` is bound to "dance with you" only within the
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;; (let ...). Let always returns the value of the last `form` in the
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;; let form.
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(let ((me "dance with you"))
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me)
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;; => "dance with you"
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; 3. Structs and Collections
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Structs
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(defstruct dog name breed age)
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(defparameter *rover*
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(make-dog :name "rover"
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:breed "collie"
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:age 5))
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*rover* ; => #S(DOG :NAME "rover" :BREED "collie" :AGE 5)
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(dog-p *rover*) ; => t ;; ewww)
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(dog-name *rover*) ; => "rover"
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2013-08-11 17:39:13 +00:00
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;; Dog-p, make-dog, and dog-name are all created by defstruct!
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2013-08-11 08:49:33 +00:00
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;;; Pairs
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;; `cons' constructs pairs, `car' and `cdr' extract the first
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;; and second elements
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(cons 'SUBJECT 'VERB) ; => '(SUBJECT . VERB)
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(car (cons 'SUBJECT 'VERB)) ; => SUBJECT
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(cdr (cons 'SUBJECT 'VERB)) ; => VERB
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;;; Lists
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;; Lists are linked-list data structures, made of `cons' pairs and end
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;; with a `nil' (or '()) to mark the end of the list
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(cons 1 (cons 2 (cons 3 nil))) ; => '(1 2 3)
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;; `list' is a convenience variadic constructor for lists
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(list 1 2 3) ; => '(1 2 3)
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;; and a quote can also be used for a literal list value
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'(1 2 3) ; => '(1 2 3)
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;; Can still use `cons' to add an item to the beginning of a list
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(cons 4 '(1 2 3)) ; => '(4 1 2 3)
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;; Use `append' to - surprisingly - append lists together
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(append '(1 2) '(3 4)) ; => '(1 2 3 4)
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2013-08-11 17:39:13 +00:00
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;; Or use concatenate -
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2013-08-20 14:57:25 +00:00
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(concatenate 'list '(1 2) '(3 4))
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;; Lists are a very central type, so there is a wide variety of functionality for
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;; them, a few examples:
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(mapcar #'1+ '(1 2 3)) ; => '(2 3 4)
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(mapcar #'+ '(1 2 3) '(10 20 30)) ; => '(11 22 33)
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(remove-if-not #'evenp '(1 2 3 4)) ; => '(2 4)
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(every #'evenp '(1 2 3 4)) ; => nil
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(some #'oddp '(1 2 3 4)) ; => T
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(butlast '(subject verb object)) ; => (SUBJECT VERB)
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2013-08-11 08:49:33 +00:00
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;;; Vectors
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;; Vectors are fixed-length arrays
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#(1 2 3) ; => #(1 2 3)
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;; Use concatenate to add vectors together
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(concatenate 'vector #(1 2 3) #(4 5 6)) ; => #(1 2 3 4 5 6)
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;;; Arrays
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;; Both vectors and strings are special-cases of arrays.
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;; 2D arrays
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(make-array (list 2 2))
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2013-08-11 17:39:13 +00:00
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;; (make-array '(2 2)) works as well.
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2013-08-11 08:49:33 +00:00
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; => #2A((0 0) (0 0))
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(make-array (list 2 2 2))
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; => #3A(((0 0) (0 0)) ((0 0) (0 0)))
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2013-08-11 17:39:13 +00:00
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;; Caution- the default initial values are
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;; implementation-defined. Here's how to define them:
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2013-08-11 17:39:13 +00:00
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(make-array '(2) :initial-element 'unset)
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; => #(UNSET UNSET)
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;; And, to access the element at 1,1,1 -
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(aref (make-array (list 2 2 2)) 1 1 1)
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; => 0
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2013-08-11 17:39:13 +00:00
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;;; Naively, sets are just lists:
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(set-difference '(1 2 3 4) '(4 5 6 7)) ; => (3 2 1)
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(intersection '(1 2 3 4) '(4 5 6 7)) ; => 4
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(union '(1 2 3 4) '(4 5 6 7)) ; => (3 2 1 4 5 6 7)
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(adjoin 4 '(1 2 3 4)) ; => (1 2 3 4)
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2013-08-11 17:39:13 +00:00
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;; But you'll want to use a better data structure than a linked list
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;; for performant work!
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2013-08-11 08:49:33 +00:00
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;;; Dictionaries are implemented as hash tables.
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;; Create a hash table
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(defparameter *m* (make-hash-table))
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;; set a value
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(setf (gethash 'a *m*) 1)
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;; Retrieve a value
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(gethash 'a *m*) ; => 1, t
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2013-08-11 17:39:13 +00:00
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;; Detail - Common Lisp has multiple return values possible. gethash
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;; returns t in the second value if anything was found, and nil if
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;; not.
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;; Retrieving a non-present value returns nil
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(gethash 'd *m*) ;=> nil, nil
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;; You can provide a default value for missing keys
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2013-08-20 14:57:25 +00:00
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(gethash 'd *m* :not-found) ; => :NOT-FOUND
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2013-08-11 17:39:13 +00:00
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;; Let's handle the multiple return values here in code.
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(multiple-value-bind
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(a b)
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(gethash 'd *m*)
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(list a b))
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; => (NIL NIL)
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(multiple-value-bind
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(a b)
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(gethash 'a *m*)
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(list a b))
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; => (1 T)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; 3. Functions
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Use `lambda' to create anonymous functions.
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;; A function always returns the value of its last expression.
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;; The exact printable representation of a function will vary...
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(lambda () "Hello World") ; => #<FUNCTION (LAMBDA ()) {1004E7818B}>
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;; Use funcall to call lambda functions
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(funcall (lambda () "Hello World")) ; => "Hello World"
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2013-08-11 17:39:13 +00:00
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;; Or Apply
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(apply (lambda () "Hello World") nil) ; => "Hello World"
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2013-08-11 08:49:33 +00:00
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;; De-anonymize the function
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(defun hello-world ()
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"Hello World")
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(hello-world) ; => "Hello World"
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;; The () in the above is the list of arguments for the function
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(defun hello (name)
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(format nil "Hello, ~a " name))
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(hello "Steve") ; => "Hello, Steve"
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;; Functions can have optional arguments; they default to nil
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(defun hello (name &optional from)
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(if from
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(format t "Hello, ~a, from ~a" name from)
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|
(format t "Hello, ~a" name)))
|
|
|
|
|
|
|
|
(hello "Jim" "Alpacas") ;; => Hello, Jim, from Alpacas
|
|
|
|
|
|
|
|
;; And the defaults can be set...
|
|
|
|
(defun hello (name &optional (from "The world"))
|
|
|
|
(format t "Hello, ~a, from ~a" name from))
|
|
|
|
|
2013-08-11 17:39:13 +00:00
|
|
|
(hello "Steve")
|
|
|
|
; => Hello, Steve, from The world
|
|
|
|
|
|
|
|
(hello "Steve" "the alpacas")
|
|
|
|
; => Hello, Steve, from the alpacas
|
|
|
|
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
;; And of course, keywords are allowed as well... usually more
|
|
|
|
;; flexible than &optional.
|
|
|
|
|
|
|
|
(defun generalized-greeter (name &key (from "the world") (honorific "Mx"))
|
|
|
|
(format t "Hello, ~a ~a, from ~a" honorific name from))
|
|
|
|
|
|
|
|
(generalized-greeter "Jim") ; => Hello, Mx Jim, from the world
|
|
|
|
|
|
|
|
(generalized-greeter "Jim" :from "the alpacas you met last summer" :honorific "Mr")
|
|
|
|
; => Hello, Mr Jim, from the alpacas you met last summer
|
|
|
|
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
;; 4. Equality
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
|
2013-08-11 17:39:13 +00:00
|
|
|
;; Common Lisp has a sophisticated equality system. A couple are covered yere.
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
;; for numbers use `='
|
|
|
|
(= 3 3.0) ; => t
|
|
|
|
(= 2 1) ; => nil
|
|
|
|
|
2013-08-11 17:39:13 +00:00
|
|
|
;; for object identity (approximately) use `eql`
|
2013-08-11 08:49:33 +00:00
|
|
|
(eql 3 3) ; => t
|
|
|
|
(eql 3 3.0) ; => nil
|
|
|
|
(eql (list 3) (list 3)) ; => nil
|
|
|
|
|
2013-08-11 17:39:13 +00:00
|
|
|
;; for lists, strings, and bit-vectors use `equal'
|
2013-08-11 08:49:33 +00:00
|
|
|
(equal (list 'a 'b) (list 'a 'b)) ; => t
|
|
|
|
(equal (list 'a 'b) (list 'b 'a)) ; => nil
|
|
|
|
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
;; 5. Control Flow
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
|
|
|
|
;;; Conditionals
|
|
|
|
|
|
|
|
(if t ; test expression
|
|
|
|
"this is true" ; then expression
|
|
|
|
"this is false") ; else expression
|
|
|
|
; => "this is true"
|
|
|
|
|
|
|
|
;; In conditionals, all non-nil values are treated as true
|
|
|
|
(member 'Groucho '(Harpo Groucho Zeppo)) ; => '(GROUCHO ZEPPO)
|
|
|
|
(if (member 'Groucho '(Harpo Groucho Zeppo))
|
|
|
|
'yep
|
|
|
|
'nope)
|
|
|
|
; => 'YEP
|
|
|
|
|
|
|
|
;; `cond' chains a series of tests to select a result
|
|
|
|
(cond ((> 2 2) (error "wrong!"))
|
|
|
|
((< 2 2) (error "wrong again!"))
|
|
|
|
(t 'ok)) ; => 'OK
|
|
|
|
|
|
|
|
;; Typecase switches on the type of the value
|
|
|
|
(typecase 1
|
2013-08-11 17:39:13 +00:00
|
|
|
(string :string)
|
|
|
|
(integer :int))
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
; => :int
|
|
|
|
|
|
|
|
;;; Iteration
|
|
|
|
|
|
|
|
;; Of course recursion is supported:
|
|
|
|
|
|
|
|
(defun walker (n)
|
2013-08-11 17:40:51 +00:00
|
|
|
(if (zerop n)
|
2013-08-11 17:39:13 +00:00
|
|
|
:walked
|
|
|
|
(walker (1- n))))
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
(walker) ; => :walked
|
|
|
|
|
|
|
|
;; Most of the time, we use DOLIST or LOOP
|
|
|
|
|
|
|
|
|
|
|
|
(dolist (i '(1 2 3 4))
|
2013-08-11 17:39:13 +00:00
|
|
|
(format t "~a" i))
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
; => 1234
|
|
|
|
|
|
|
|
(loop for i from 0 below 10
|
2013-08-11 17:39:13 +00:00
|
|
|
collect i)
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
; => (0 1 2 3 4 5 6 7 8 9)
|
|
|
|
|
|
|
|
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
;; 6. Mutation
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
|
|
|
|
;; Use `setf' to assign a new value to an existing variable. This was
|
|
|
|
;; demonstrated earlier in the hash table example.
|
|
|
|
|
|
|
|
(let ((variable 10))
|
2013-08-11 17:39:13 +00:00
|
|
|
(setf variable 2))
|
|
|
|
; => 2
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
|
|
|
|
;; Good Lisp style is to minimize destructive functions and to avoid
|
|
|
|
;; mutation when reasonable.
|
|
|
|
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
;; 7. Classes and Objects
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
|
|
|
|
;; No more Animal classes, let's have Human-Powered Mechanical
|
|
|
|
;; Conveyances.
|
|
|
|
|
|
|
|
(defclass human-powered-conveyance ()
|
2013-08-11 17:39:13 +00:00
|
|
|
((velocity
|
|
|
|
:accessor velocity
|
|
|
|
:initarg :velocity)
|
|
|
|
(average-efficiency
|
2013-08-20 14:57:25 +00:00
|
|
|
:accessor average-efficiency
|
|
|
|
:initarg :average-efficiency))
|
2013-08-11 17:39:13 +00:00
|
|
|
(:documentation "A human powered conveyance"))
|
|
|
|
|
|
|
|
;; defclass, followed by name, followed by the superclass list,
|
|
|
|
;; followed by slot list, followed by optional qualities such as
|
|
|
|
;; :documentation.
|
|
|
|
|
|
|
|
;; When no superclass list is set, the empty list defaults to the
|
|
|
|
;; standard-object class. This *can* be changed, but not until you
|
|
|
|
;; know what you're doing. Look up the Art of the Metaobject Protocol
|
|
|
|
;; for more information.
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
(defclass bicycle (human-powered-conveyance)
|
2013-08-11 17:39:13 +00:00
|
|
|
((wheel-size
|
|
|
|
:accessor wheel-size
|
|
|
|
:initarg :wheel-size
|
|
|
|
:documentation "Diameter of the wheel.")
|
|
|
|
(height
|
|
|
|
:accessor height
|
|
|
|
:initarg :height)))
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
(defclass recumbent (bicycle)
|
2013-08-11 17:39:13 +00:00
|
|
|
((chain-type
|
|
|
|
:accessor chain-type
|
|
|
|
:initarg :chain-type)))
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
(defclass unicycle (human-powered-conveyance) nil)
|
|
|
|
|
|
|
|
(defclass canoe (human-powered-conveyance)
|
2013-08-11 17:39:13 +00:00
|
|
|
((number-of-rowers
|
|
|
|
:accessor number-of-rowers
|
|
|
|
:initarg :number-of-rowers)))
|
|
|
|
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
;; Calling DESCRIBE on the human-powered-conveyance class in the REPL gives:
|
|
|
|
|
|
|
|
(describe 'human-powered-conveyance)
|
|
|
|
|
|
|
|
; COMMON-LISP-USER::HUMAN-POWERED-CONVEYANCE
|
|
|
|
; [symbol]
|
|
|
|
;
|
|
|
|
; HUMAN-POWERED-CONVEYANCE names the standard-class #<STANDARD-CLASS
|
|
|
|
; HUMAN-POWERED-CONVEYANCE>:
|
|
|
|
; Documentation:
|
|
|
|
; A human powered conveyance
|
|
|
|
; Direct superclasses: STANDARD-OBJECT
|
|
|
|
; Direct subclasses: UNICYCLE, BICYCLE, CANOE
|
|
|
|
; Not yet finalized.
|
2013-08-20 14:57:25 +00:00
|
|
|
; Direct slots:
|
2013-08-11 08:49:33 +00:00
|
|
|
; VELOCITY
|
|
|
|
; Readers: VELOCITY
|
|
|
|
; Writers: (SETF VELOCITY)
|
|
|
|
; AVERAGE-EFFICIENCY
|
|
|
|
; Readers: AVERAGE-EFFICIENCY
|
|
|
|
; Writers: (SETF AVERAGE-EFFICIENCY)
|
|
|
|
|
|
|
|
;; Note the reflective behavior available to you! Common Lisp is
|
|
|
|
;; designed to be an interactive system
|
|
|
|
|
|
|
|
;; To define a method, let's find out what our circumference of the
|
2013-08-11 17:39:13 +00:00
|
|
|
;; bike wheel turns out to be using the equation: C = d * pi
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
(defmethod circumference ((object bicycle))
|
2013-08-11 17:39:13 +00:00
|
|
|
(* pi (wheel-size object)))
|
|
|
|
|
|
|
|
;; pi is defined in Lisp already for us!
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
;; Let's suppose we find out that the efficiency value of the number
|
2013-08-11 17:39:13 +00:00
|
|
|
;; of rowers in a canoe is roughly logarithmic. This should probably be set
|
|
|
|
;; in the constructor/initializer.
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
;; Here's how to initialize your instance after Common Lisp gets done
|
|
|
|
;; constructing it:
|
|
|
|
|
|
|
|
(defmethod initialize-instance :after ((object canoe) &rest args)
|
|
|
|
(setf (average-efficiency object) (log (1+ (number-of-rowers object)))))
|
|
|
|
|
|
|
|
;; Then to construct an instance and check the average efficiency...
|
|
|
|
|
|
|
|
(average-efficiency (make-instance 'canoe :number-of-rowers 15))
|
|
|
|
; => 2.7725887
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
;; 8. Macros
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
|
|
|
|
;; Macros let you extend the syntax of the language
|
|
|
|
|
|
|
|
;; Common Lisp doesn't come with a WHILE loop- let's add one.
|
|
|
|
;; If we obey our assembler instincts, we wind up with:
|
|
|
|
|
|
|
|
(defmacro while (condition &body body)
|
|
|
|
"While `condition` is true, `body` is executed.
|
|
|
|
|
|
|
|
`condition` is tested prior to each execution of `body`"
|
|
|
|
(let ((block-name (gensym)))
|
|
|
|
`(tagbody
|
2013-08-11 17:39:13 +00:00
|
|
|
(unless ,condition
|
2013-08-11 08:49:33 +00:00
|
|
|
(go ,block-name))
|
|
|
|
(progn
|
|
|
|
,@body)
|
|
|
|
,block-name)))
|
|
|
|
|
|
|
|
;; Let's look at the high-level version of this:
|
|
|
|
|
|
|
|
|
|
|
|
(defmacro while (condition &body body)
|
|
|
|
"While `condition` is true, `body` is executed.
|
|
|
|
|
|
|
|
`condition` is tested prior to each execution of `body`"
|
|
|
|
`(loop while ,condition
|
|
|
|
do
|
2013-08-11 17:39:13 +00:00
|
|
|
(progn
|
|
|
|
,@body)))
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
;; However, with a modern compiler, this is not required; the LOOP
|
|
|
|
;; form compiles equally well and is easier to read.
|
|
|
|
|
2013-08-11 17:39:13 +00:00
|
|
|
;; Note that ``` is used, as well as `,` and `@`. ``` is a quote-type operator
|
|
|
|
;; known as quasiquote; it allows the use of `,` . `,` allows "unquoting"
|
2013-08-11 08:49:33 +00:00
|
|
|
;; variables. @ interpolates lists.
|
|
|
|
|
|
|
|
;; Gensym creates a unique symbol guaranteed to not exist elsewhere in
|
|
|
|
;; the system. This is because macros are expanded at compile time and
|
|
|
|
;; variables declared in the macro can collide with variables used in
|
|
|
|
;; regular code.
|
|
|
|
|
|
|
|
;; See Practical Common Lisp for more information on macros.
|
2013-08-13 15:19:56 +00:00
|
|
|
```
|
2013-08-11 08:49:33 +00:00
|
|
|
|
|
|
|
|
|
|
|
## Further Reading
|
|
|
|
|
|
|
|
[Keep moving on to the Practical Common Lisp book.](http://www.gigamonkeys.com/book/)
|
|
|
|
|
|
|
|
|
|
|
|
## Credits.
|
|
|
|
|
|
|
|
Lots of thanks to the Scheme people for rolling up a great starting
|
|
|
|
point which could be easily moved to Common Lisp.
|
2013-08-11 17:39:13 +00:00
|
|
|
|
|
|
|
- [Paul Khoung](https://github.com/pkhuong) for some great reviewing.
|