Introduction to Lisp Programming (DrRacket)

Merrill McKee – TAmerrillmck@yahoo.comTom Cool – TAtomcool@knights.ucf.edu

Why learn Lisp?

As a computer scientist, learn to think functionally One of three major programming language paradigms:

Functional, Procedural, Object-Oriented Lisp is the oldest and premier functional language

(Lisp has actually grown into a multi-paradigm language, and includes procedural facilities.)

Many programmers learn to love Lisp

Perhaps I like Lisp because of some quirk in the way my brain is wired.” -- Peter Seibel

Why learn Lisp?

Still used in industry As extendable and as fast [1] as other languages Stable, powerful

Web, GUI, open source libraries Read-eval-print loop (REPL)

NASA’s 1998 Deep Space 1 mission Common in Artificial Intelligence PhD qualifying exam Or for your COP 4020 exams and homework

References on last slide

History of Lisp

Created by John McCarthy in the late 1950’s Published in 1960 Championed mathematical logic to study

artificial intelligence Main idea was to study computability from a

functional programming standpoint

Dialects - Common Lisp

In the 1980s, the Common Lisp language specification attempted to standardize existing Lisp variants

Later standardized by ANSI X3.226-1994 Now supports object oriented, imperative,

and functional programming

Common Lisp - Resources

“Practical Common Lisp” by Peter Seibel is available in electronic version at UCF Library “One Search”

“Common LISP, A Gentle Introduction to Symbolic Computation,” by David Touretzky is recommended

Dialects – Scheme

Developed in late 1970s at MIT by Steele and Sussman

Minimalist Textbook uses Scheme

"Although we write our program interpretation and transformation systems in Scheme, any language that supports both first-class procedures and assignment (ML, Common Lisp, Python, Ruby etc.) is adequate for working the exercises."

Daniel P. Friedman and Mitchell Want, Essentials of Programming Languages,

[Cambridge, Mass: The MIT Press]: xix.

Dialects – Racket

Developed in late 1990s by Matthias Felleisen

Racket can be considered: a programming language—a dialect of Lisp and a

descendant of Scheme; a family of programming languages—variants of Racket,

and more; or a set of tools—for using a family of programming

languages.

Dialects – Racket

One tool is the Dr. Racket IDE Homework will be graded in Racket

Getting Started - Examples

Numeric Literals Characters

Strings Functions

Functions Macros Special

Operators

Numeric Literals

Oops (the debugger)

Clicking on the stop signsOpens the Backtrace

Defining Functions Fundamental building

block for Lisp programs

Most common type of Lisp test question! Define a function

that …

Definitions Window

Interactions Window

Lambda Calculus

Invented by Church and Kleene in the 1930’s

Can be used to define what a computable function is

Influenced functional programming languages such as Lisp, ML, and Haskell

f(x) = x + 2 …or… lambda x . x + 2 Binds functions to names

Gives a natural representation for recursion

Lisp Lambda Functions

(lambda lambda-list body)

Similar to lambda calculus expr.: lambda x . x + 2

Fundamental Data Types

A list is a sequence of elements, where each element can be another list

Fundamental Data Types

Racket also provides Vectors Hash tables I/O Arrays

The Interpreter

In 1965 McCarthy developed a function called “eval” used to evaluate other functions (an interpreter).

It is a read-evaluate-write infinite loop. Expressions are interpreted by the function “eval.” Literals are evaluated to themselves. For example,

if you type in 5, the interpreter will return 5. Expressions that are calls to primitive functions are

evaluated as follows: Each parameter is evaluated first. The primitive function is applied to the parameter values. The result is displayed.

Eval Function

Sample Problems What do the following evaluate to?

(Use your intuition and guess. No grade here. In the spirit of the class, please come up with an answer before using your laptop to find a solution.)

(+ (3 2)) (if (< 2 3) (print “Yes”) (print “No”)) (if (< 2 3) (print “1”) (print “2”) (print “3”)) z (x 1 “foo”) … or … ‘(x 1 “foo”) (+) (+ 1) (dotimes (x 2) (print x)) (null nil) () (sort ‘(1 2 3) #’>) (eq 1 1.0) or maybe (eql 1 1.0) (equal 1 1.0) (equalp 1 1.0)

Answers to Sample Problems

Only two evaluate correctly:

> (if(< 2 3)(print "Yes")(print "No"))"Yes“

> (+)0

The rest throw exceptions due to syntax errors, typically references to an identifier before its definition (e.g., nil, eq, eql are all undefined)

Binding Names to Functions

Define is used to bind a name to a value or a lambda expression.

Format(define function_name (lambda (parameters)

<expression(s)>)

Example:(define square_num

(lambda (n) (* n n)))

Binding Names to Functions (cont)

Binding Names to Values

(define pi 3.14)(define twopi (* 2 pi))

Once these two expressions are typed in to the Lisp interpreter, typing pi will return 3.14.

Names consist of letters, digits, and special characters (except parenthesis)

If

John McCarthy invented the if-then-else construct we take for granted. It was incorporated into Algol.

(if condition then-form [else-form]) The then-form and optional else-form are

restricted to a single lisp form.

If (Cond)

Cond is a macro to handle multiple nested if statements.

> (cond [(positive? -5) (error "doesn't get here")] [(zero? -5) (error "doesn't get here, either")] [(positive? 5) 'here])'here

If

Sample problem

Is x 2n, where n is all positive integers?∈

Functional solution:Recursively subtract 2 from x.If x = 0, x 2n, else x 2n∈ ∉

Solution to sample problem

References For These Slides

UCF Library – about 20-25 books in the QA 76.73 .L23 … shelf. Practical Common Lisp by Peter Seibel Common Lisp The Language by Guy

Steele, Jr. Dr. Montagne’s UCF COP 4020 Slides Websites

http://mypage.iu.edu/~colallen/lp/ concise and readable

http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node1.html extensive but harder to read

http://www.google.com