Introduction to Lisp 1

1
Introduction to Lisp 1

• Carlos Lollett

2
Introduction to Lisp. Contents

• What is Lisp
• Expressions
• Functions
• Lists
• Examples

3
What is Lisp

• LISP means "LISt Processor", is a functional
  language
• LISP was designed as an interpreted language. One
  of the strongest features of LISP is that it
  treats programs as same as data. An intelligent
  LISP program can evolve and change its code!

4
Expressions

• Evaluation Loop
• loop
• read in an expression from the console
• evaluate the expression
• print the result of evaluation to the console
• end loop.

5
Expressions

• Atoms
• An atom is the unit in LISP.
• Any combination of characters, except " ", "("
  and ")", can be an atom.
• Types of Atom
• Symbols
• Not case sensitive.
• Numbers
• Integers
• Rational
• Complex C(i j)
• Constants (self-evaluating)
• Symbols that have special meaning like NIL, T

6
Expressions

• Forms
• Functions f(x) gt (f x)
• Prefix notation gt ( 2 (cos 0) ( 4 6))
• Overloading

7
Bindings

• Variable binding
• Variables equal to symbols
• We can associate a value to the variable "a", by
  the function "setq"
• (setq myval 3)
• gt myval
• 3

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Bindings

• Variable Literal value
• symbol myval" means myval" or 3 ? We should use
  the QUOTE. QUOTE is an essential function in
  LISP, it can be used in two ways
• gt myval
• MYVAL
• gt (quote myval)
• MYVAL
• (eval myval) eval is opposite to quote
  
• 3

9
Defining Functions

• (defun double (x) ( x 2))
• (defun factorial (N) "Compute the factorial of
  N." (if ( N 1) 1 ( N (factorial (- N 1)))))
• (defun fibonacci (N) "Compute the N'th Fibonacci
  number." (if (or (zerop N) ( N 1)) 1 (
  (fibonacci (- N 1)) (fibonacci (- N 2)))))

10
Coding Lisp out of the interpreter

• Start with acl
• (compile-file "testing.lisp")
• (load "testing")
• (trace factorial) to trace functions
• (exit) exit acl environment

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Lists

• (cons 1 (cons 2 nil))
• (1 2)
• USER(24) (first '(2 4 8))
• 2
• USER(25) (rest '(2 4 8))
• (4 8)
• USER(26) (first (rest '(2 4 8)))
• 4
• USER(27) (rest (rest '(2 4 8)))
• (8)
• USER(28) (rest (rest (rest '(8))))
• NIL
• USER(29) (null nil)
• T
• USER(30) (null '(1 2 3))
• NIL
• USER(31) (consp nil)
• NIL
• USER(32) (consp '(1 2 3))

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List Recursive Function

• (defun recursive-list-length (L) "A recursive
  implementation of list-length." (if (null L) 0 (
  1 (recursive-list-length (rest L)))))