Introduction to Lisp Programming

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Introduction to Lisp Programming

• Merrill McKee TA
• merrillmck_at_yahoo.com

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Why learn about Lisp?

• Lisp programmers love Lisp
• Perhaps I like Lisp because of some quirk in the
  way my brain is wired. Peter Seibel
• 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)
• NASAs 1998 Deep Space 1 mission
• Common in Artificial Intelligence
• PhD qualifying exam
• Or just for your grade on homework 2 and COP
  4020 exams

References on last slide
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Common Lisp

• Common Lisp, a dialect of Lisp, is the language
  specification that was attempted in the 1980s to
  standardize existing Lisp variants
• Scheme
• Later standardized by ANSI X3.226-1994

• Your homework assignment will be done in Common
  Lisp

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Getting Started (link for more info)

• Countless Lisp development environments

Cygwin or Unix/Linux prompt
Emacs
Lispworks
Eclipse w/ plugin
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Getting Started - Examples

• Numeric Literals
• Characters
• Strings
• Functions
• Functions
• Macros
• Special Operators

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Numeric Literals
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Oops (the debugger)
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Defining Functions

• Fundamental building block for Lisp programs
• Most common type of Lisp test question!
• Define a function that

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History of Lisp

• Created by John McCarthy in the late 1950s
• Published in 1960
• Championed mathematical logic to study artificial
  intelligence
• Main idea was to study computability from a
  functional programming standpoint
• Common Lisp now supports object oriented,
  imperative, and functional programming

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Lambda Calculus

• Invented by Church and Kleene in the 1930s
• 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

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Lisp Lambda Functions

• (lambda lambda-list body)
• Similar to lambda calculus expr.
• lambda x . x 2

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Fundamental Data Types

• Two fundamental data types
• Atoms
• An atom is an alphanumeric string, used either as
  a variable name or a data item
• Lists
• A list is a sequence of elements, where each
  element is either an atom or a list
• Common Lisp also provides
• Vectors
• Hash tables
• I/O
• Arrays and Multi-dimensional arrays

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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.

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Eval Function
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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 (lt 2 3) (print Yes) (print No))
• (if (lt 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) gt)
• (eq 1 1.0) .. (eql 1 1.0) (equal 1 1.0)
  (equalp 1 1.0)

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Binding Names to Functions

• Define or defun is used to bind a name to a
  value or a lambda expression.
• Depends on the Lisp environment
• Format
• (defun (function_name parameters)
  ltexpression(s)gt)
• Formally - defun name lambda-list
  declaration doc-string form
• Example
• (defun (square num) ( num num))

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Binding Names to Functions (cont)

• Once the function is evaluated by the
  interpreter, it can be used as in (square 7) 49
• Example
• (define (hypotenuse side1 side2)
• (sqrt ( (square side1) (square side2))))

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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) but cannot begin
  with a digit.

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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. To create a
  code block use the progn function.
• Alternatively, use when and unless macros.

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If (Cond)

• Cond is a macro to handle multiple nested if
  statements.
• (cond
• (test-1 form)
• (test-n form))

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If
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If
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Setf

• Binds a value to a location/variable
• (setf place value)

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Sample problem

• How would you reverse a list? Do you have enough
  tools yet to define this function?
• Without using the built-in reverse function
• (defun reverse-list (list) )
• What do you need?
• Need to get an element from the list
• Need to build and save a new list
• Need to do it in reverse order

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My-reverse

• http//mwolson.org/notes/wikisource/CommonLispBegi
  nnersGuide.muse

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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. Montagnes UCF COP 4020 Slides
• Websites
• http//mypage.iu.edu/colallen/lp/ concise and
  readable
• http//www.cs.cmu.edu/Groups/AI/html/cltl/clm/node
  1.html extensive but harder to read
• http//www.google.com