a quick introduction to lisp

8/14/2019 A Quick Introduction to Lisp

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A Quick Introduction to Lisp

M. Habibullah Pagarkar


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http://xkcd.com/297/


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Syntax

Expression oriented language

Consists of many expressions or forms

3 Kinds of expressions

Literals: 0.42e2, hello, #\c, #(1 2)

Symbols: a-symbol

Lists: (f x y)


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Numerical Nonsense

Number

Real

Rational Integer

Fixnum Bignum

Ratio

Float Short-float

Single-float

Double-float

Long-float

Complex


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Variables

Lexical scope

Variables have no types. Objects do

Symbols are evaluated as variables

Bound

Unbound

A symbol differs from it's printedrepresentation

'ooga and 'ooga\ booga

Interning


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Packages

Namespacing

Symbol '*package*' stores the currentpackage

Exporting symbols

External symbols package:name

Internal symbols package::name Keyword package


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So these are like Ruby'ssymbols, right? Wrong.

Common Lisp symbols Ruby symbols

Unique in a package Globally unique

Can have spaces in a name Can't

Can be uninterned Can't

Symbols carry data Used only for identification

Contain a property list Don't

Are candidates for GC if unbound Aren't

Lisp symbols in the keyword package are analogous to Ruby symbols


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Cons Cells

(cons 1 2) (1 . 2)

(cons 1 '()) '(1)

From wikipedia


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Read-Eval-Print-Loop

Read form input Lisp object

Eval input object output object

Print output object using some sort ofprint representation

Loop


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Evaluation

Literals are self evaluating

Symbols are looked up in lexical scope

Lists

Function name as first element

All subsequent symbols are evaluated

Function called with these params

Eager evaluation is default behaviour


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Preventing Evaluation

Special form (quote expression)

Abbreviated as '(expression)


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Comments

;;;

;;

;

#|

Block comment

|#


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Booleans

t and nil are constants

(or exp1 exp2)

(and exp1 exp2)

(if test exp1 exp2)

(cond (test-1 consequent-1)

(test-n consequent-n))


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Equality Excesses

eq Symbols

eql Numbers of the same type - default

equal Lists

= Best for numbers

equalp Equality predicate

string-equals Strings


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Regular and Special Functions

(function hello)

Or simply #'hello

(defun hello ()

Do not mind me. I am a string.

(print hello))


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I wanna know more!

describe

type-of

boundp

fboundp

apropos

documentation


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eval ~ apply


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Side Effects

(setf a 5)

(random 10)

(defvar b 10)

(defparameter my-list '(10 20))

(let ((var-1 val-1)

(var-n val-n))(body))

let*


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LIStProcessing

'() nil

(cons 1 (cons 2 (cons 3 nil)))

(list 1 2 3)

'(1 2 3)

listp, endp, first, second, tenth,rest, car, cdr, cadr, cdddr,member, intersection, nth,nthcdr, append, butlast, reverse,remove etc


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List Processing

assoc, rassoc

subst

sublis


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Destructive List Surgery

nconc, nsubst, nreverse, nunion,nintersection, delete


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Applicative Programming

funcall

map and it's brethren

lambda

reduce, every

find-if, remove-if, remove-if-not,count-if, count-if-not (filter)


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Recursion

Ideas for tail recursive functions

(defun func (x)

(cond (end-test end-val)

(t (func reduced-x))))

(labels ((fn-1 args-1 body-1)

(fn-n args-n body-n))body)


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IO, IO, off to work we go

(format t ~s to ~s~% is the timelimit 1 2)

read

yes-or-no-p, y-or-n-pwith-open-file


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Assignment

incf, decf, push, pop when, unless


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Iteration

(dotimes (var n (result-form))

body)

(dolist (var list (result-form))

body) return

(do ((var1 init1 update1)

(varn initn updaten))

(test action1 actionn)

body)


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Blocks

Function bodies are implicit blocks

return-from

block

prog1, prog2, progn


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Conditions and Restarts

break, error, warn, cerror


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Function Parameters

(defun foo (x &optional (y 2) (z5) ())

&rest

&key &aux


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Simple Objects

Arrays

Property Lists

Structures

Hash Tables


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Macros

Way to extend Lisp's syntax

Express concepts concisely

Expanded at compile time

It creates an expression that Lisp evals

(defmacro my-incf (var)

(list 'setq var (list '+ var 1)))

(defmacro my-incf (var)

`(setq ,var (+ 1 ,var)))


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Functions Macros

Arguments are alwaysevaluated

Arguments are neverevaluated

Results can be anyvalue/s

Results can only be avalid s-expression

Results aren't evaluated Results are evaluated

What's the difference?


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To confuse you a little more

` , ,@ &body

Destructuring

defvar, defparameter, defconstant


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Object Orientation

Older Object Systems Flavours: Introduced Message passing,

multiple inheritance & mixins

New Flavours: Generic functions Common LOOPS

CLOS


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A CLOS Encounter

Class, instances of classes, genericfunctions and methods

defclass, make-instance,

defgeneric, defmethod Class has multiple superclasses, slots

and a meta-class

Multiple dispatch Methods defined separately with no

special access

Multiple Dispatch & Generic


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Multiple Dispatch & GenericFunctions

Given args, a list of applicable methods isfound

Find the most specific method

Apply that method to the args

Example: (defgeneric f (x y))

(defmethod f ((x integer) y) 1) (f 1 2.0) 1

(defmethod f ((x integer) (y real)) 2)

(f 1 2.0) 2


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Lisp and MacGyverLisp and MacGyver

Yes, these are shamelessly stolen too


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What do you mean MacGyver?

Mid 80s to early 90s Prefer brain over brawn

Used only simple tools

Clever solutions to seemingly intractable problems* Entered into popular culture

Suffered from bad marketing towards the end

Spin-offs never as good as the original

Some loyal old-timers still act like keepers of the flame

* Hey! Wikipedia says so.


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http://xkcd.com/224/

S h h d?


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So what happened?

Worse is betterhttp://www.dreamsongs.com/WIB.html

H h it ?


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Hmm, so who uses it now?

ITA Software Lisp for High-Performancetransaction processing (Cambridge, MA)

Cleartrip (Bombay)

Naughty Dog Software

Stumpwm

Movitz

Oh and this little OS called Emacs

Wh t b t TDD?


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What about TDD?

LispUnit FiveAM

Stefil

LIFT

cl-unit

and others

B k C Li


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Books on Common Lisp

ANSI Common Lisp - Paul Graham Practical Common Lisp - Peter Seibel

On Lisp - Paul Graham

Paradigms of AI Programming PeterNorvig

Lisp Winston and Horn

B k S h


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Books on Scheme

The Little Schemer series DanielFriedman and Matthias Felleisen

SICP - Gerald Sussman and Harold

Abelson The Scheme Programming Language

Kent Dybvig

Teach Yourself Scheme in Fixnum Days Dorai Sitaram

Upcoming Books


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Upcoming Books

Land of Lisp Conrad Barski (2010)www.lisperati.com

Lisp Outside the Box Nick Levine (2010)

Which Lisp?


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Which Lisp?

Linux SBCL* Mac OS X Clozure CL*

Windows Corman CL, Allegro CL,

LispWorks, CLISP* Or try Scheme/Clojure

Try to accept Emacs :)

http://gigamonkeys.com/lispbox/

http://common-lisp.net/~dlw/LispSurvey.html

* Open Source
http://common-lisp.net/~dlw/LispSurvey.htmlhttp://common-lisp.net/~dlw/LispSurvey.html

a quick introduction to lisp

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