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Introduction 2 Lisp Part I

Andreas Wichert

LEIC-T(Página da cadeira: Fenix)

Corpo docenten  Andreas (Andrzej) Wichert –Praticas

n  andreas.wichert@tecnico.ulisboa.ptn  tel: 214233231n  room: N2 5-7n  http://web.tecnico.ulisboa.pt/andreas.wichert/

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Horário de dúvidas

n  5º-feira, 14H-17H, 2-N5.7

Guess:What does “LISP” stand for?

n Looney Idiotic Stupid Professor?

n Long Incomprehensible String of Parentheses?

n  LISt Processing?

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What is LISP? n Originated by John McCarthy (September

4, 1927 – October 24, 2011)n  In 1959 as an implementation of recursive

function theory

n  http://www-formal.stanford.edu/jmc/

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What is LISP? n Conditionals - if-then-else constructn A function type - functions are first-class

objectsn Recursionn Typed values rather than typed variablesn Garbage collection (interpreter)n Programs made entirely of functional

expressions that return values

Uses Polish notation

n The description "Polish" refers to the nationality of logician Jan Łukasiewicz, (21 December 1878 – 13 February 1956) who invented (prefix) Polish notation in the 1920sn  Polish notation, also known as Polish prefix

notation or simply prefix notation

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n  (5 − 6) × 7=

n Can be written as

n  ( × (− 5 6) 7)

n When Polish notation is used as a syntax for mathematical expressions by programming language interpreters, it is readily parsed into abstract syntax trees and can, in fact, define a one-to-one representation for the same

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n  ((15 ÷ (7 − (1 + 1))) × 3) − (2 + (1 + 1)) = 5

n  ((15 ÷ (7 − (1 + 1))) × 3) − (2 + (1 + 1)) = 5

n  In Lisp

n  (- (* (/ 15 (- 7 (+ 1 1))) 3) (+ 2 (+ 1 1))))5

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Literaturen Practical Common Lisp, Peter Seibel,

2005, Apress, versa o online n ANSI Common Lisp, Paul Graham, 1995,

Prentice Hall, versa o online

n  Introduca o a Linguagem Lisp , Anto nio Leita o, 1995, Instituto Superior Te cnico

My recommendation….LAND OF LISP, Conrad Barski, 2010, No Starch Press,http://landoflisp.com“A very good first contact with the world of Lisp!”"Turns out the border between genius and insanity is a pretty cheery place" says Paul Graham!

Land of Lisp - The Music Video (Home Work 1, watch the video)

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n Conrad Barski

Conrad Barski, M.D.

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n Dana Nau

n  Introduction to Lisp / AI material

n  https://www.cs.umd.edu/users/nau/

We will use Common lisp Jn Purpose of Common Lisp: to unify the

main dialects n Thus it contains multiple constructs to do

the same things n  Common Lisp (CL) is a dialect of the Lisp

programming language, published in ANSI standard document ANSI INCITS 226-1994 (R2004) (formerly X3.226-1994 (R1999)).

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Installing Common Lispn CLISP

n Download a CLISP installer from n  http://clisp.cons.org/.

Running clisp

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Clozure Common Lispn  http://ccl.clozure.com

n  Like all Common Lisp environments, CLISP will automatically place you into a read-eval-print loop (REPL)

n The code on the previous slide runs interpretively

•  A few Common Lisps will compile the code every time you load it

n Compiling makes your programs run faster, and may detect some errors

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Evaluating>1 1 >pi3.1415926535897932385L0> tT> nilNIL

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Symbolsn Common Lisp symbols are typically made

up of letters, numbers, and characters like + - / * = < > ? ! _

n  ice9, my-killer-app27, and even --<<==>>--.

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Numbers> (+ 1 1.0) 2.0 > (expt 53 53) 243568481650227121324776065201047255185334531286856408445051308795767206091502 23301256150373

> (/ 4 6)2/3 > (/ 4.0 6) 0.6666667

> (- 5 6 7)-8

Why?Evaluates from left>(- (- 5 6) 7)-8

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Strings(princ "Tutti Frutti")Tutti Frutti Tutti Frutti "Tutti Frutti"

n  The text appears twicen  First, we see the actual printing caused by

the princ command . n  REPL will always show the result of

evaluating the entered expression•  the princ function returns a value, the source

string.

> (princ "He yelled \"Stop that thief!\" from the busy street.")He yelled "Stop that thief!" from the busy street."He yelled \"Stop that thief!\" from the busy street."

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Code Mode

n  > (expt 2 3) n  8

n This calculates 2^3 = 8n  It does this by calling expt, which

computes an exponent.

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Data Mode > '(expt 2 3) (EXPT 2 3)The single quote tells Lisp to treat the subsequent form as a chunk of data—simply a list of items.

> (quote (expt 2 3))(EXPT 2 3)

> '(1 2 3)(1 2 3)

> ''(1 2 3)'(1 2 3)

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But (Why? Read the error message)> ( 1 2 3)

*** - EVAL: 1 is not a function name; try using a symbol insteadThe following restarts are available:USE-VALUE :R1 Input a value to be used instead.ABORT :R2 Abort debug loopABORT :R3 Abort debug loopABORT :R4 Abort debug loopABORT :R5 Abort main loop

Predicates

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Numerical predicates (> 5 4 3) T  (> 5 4 6) NIL (<= 3 2) NIL (= 1 2) NIL  (= 1 1 1) T  >(zerop 0) T  >(integerp 5)T

n  >  (eq 1234567890 1234567890)???

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n The eq function is the simplest of all the Lisp comparison functions, and it’s also very fast.

n  It doesn’t really work for comparing items besides symbols

n The eql command is similar to the eq command, but unlike eq, it also handles comparisons of numbers and characters

n The equalp command is essentially the same as the equal command, except that it can handle some difficult comparison cases with a bit of extra sophisti- cation

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Atoms n Every Lisp object is either an atom or a

list

Lists in Lisp n A cons cell looks like this:

n  We create the list '(1 2 3)

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Lists

Dot notation

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The cons Function link any two pieces of data

>(cons 'chicken 'cat) (CHICKEN . CAT) > (cons 'chicken 'nil) (CHICKEN) > (cons 'chicken ()) (CHICKEN) > (cons 'beef (cons 'chicken nil))(BEEF CHICKEN)

> (cons 'beef (cons 'chicken nil))(BEEF CHICKEN)

>(cons 'pork '(beef))(PORK BEEF)

> (cons 'pork '(beef chicken))(PORK BEEF CHICKEN)

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The car and cdr Functions > (car '(pork beef chicken)) PORK

> (cdr '(pork beef chicken)) (BEEF CHICKEN)

> (cdr '(pork beef chicken)) (BEEF CHICKEN) > (car '(beef chicken)) BEEF > (car (cdr '(pork beef chicken))) BEEF > (cadr '(pork beef chicken)) BEEF

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Nested Lists n  Lists can contain other lists.

'(cat (duck bat) ant)

>(car '((peas carrots tomatoes) (pork beef chicken))) (PEAS CARROTS TOMATOES)

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if> (if (= (+ 1 2) 3) 'yup 'nope) YUP

>(if (= (+ 1 2) 4) 'yup 'nope) NOPE

>(if '(1) 'the-list-has-stuff-in-it 'the-list-is-empty) THE-LIST-HAS-STUFF-IN-IT

>(if '() 'the-list-has-stuff-in-it 'the-list-is-empty) THE-LIST-IS-EMPTY

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> (if (oddp 5) 'odd-number 'even-number) ODD-NUMBER

> (if (oddp 5) 'odd-number (/ 1 0)) ODD-NUMBER

Why? Special form, executes only the true branch

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Defining Global Variables

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Local Variables

Editor

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To load / compilen  (load <nome-ficheiro>)

n  (load “projecto.lisp”)

n  (compile-file "projecto")

n  (load "projecto")

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