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Lisp Recitation cse471598

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Title: Lisp Recitation cse471598

1
Lisp Recitation (cse471/598)

Lei Tang

2
Outline

Lisp syntax
Commands for slime
How to handle problems?

3
Lisp vs. scheme

CL is a large language, including packages,
arrays, structures, hash tables, object-oriented
programming features, MACRO
Numbers different format support
Scheme language does not define an internal
representation for programs
Minor variations in syntax

4
Lisp vs. Java C

Java Object Oriented Programming.
Lisp CLOS providing more object oriented
programming concepts than Java
The difference between Lisp and Java, as Paul
Graham has pointed out, is that Lisp is for
working with computational ideas and expression,
whereas Java is for expressing completed
programs.

5
Functional Programming

Function is the basic element. Both data and
function are treat as object. The parameter could
be a function.
Basic rule the parameters of a function should
not be changed. (But there are some exceptions
like sort, incf, decf)

6
Expression Evaluation

You type an expression, the interpreter responds
by displaying the results of the evaluation of
that expression. Ex.
486
The interpreter will respond
486
Compound expressions are formed by combining
other expressions.
( 137 349)
486
The leftmost element in the list is the operator
and the other elements are operands.

7
Data Structure - Lists

Using Quote-
(1 2 3) also (quote ( 1 2 3))
(1 2 3)
Using CAR-
(CAR ( 1 2 3 4))
1
Using CDR-
(CDR ( 1 2 3))
( 2 3)

Using Cons -
(cons 0 (1 2 3))
adds the element 0 to the head of the list (1 2
3)
(0 1 2 3)
Using Append
(append (1 2) (3 4 5))
Creates a new list out of existing lists
(1 2 3 4 5)
List can also be interpreted as sets, hashtables,
trees,sequences, stacks, asscoiation-lists.

9
ITERATION

Using dolist -
(dolist (x (1 2 3)) (print x))
repeats a set of operations for as many times as
there are entries in a list.
1
2
3
nil
Using dotimes -
(dotimes (x 3) (print x))
repeats a set of operations fixed number of
times.
1
2
3
nil

Using LOOP
(loop for x from 1 to 3
do (print x)
collect x)
1
2
3
(1 2 3)
There are lot of other loop keywords like
always, never, thereis, etc.,

11
Conditional Constructs

Using CASE. (like switch in java and c)
(case 2
(1 one)
(2 two)
(3 three)
(otherwise many))
TWO

12
Defining functions using defun
(defun funct1 (x) ( x 1)) FUNCT1 (funct1 3) 4
13
RECURSION
Compute factorial (defun factorial (n)
(if ( n 0) 1 ( n (
factorial (- n 1) ) ) ) )

14
Creating Variables

Using setf to create global variables
(setf var element)
element
var
element
let (let) to create local variables

15
Input and Output
gt (progn (format t Please enter your
name ) (read-line)) gt (prin1
hello) Note There are many variants. You need
to refer to a CL book.
16
Other Important Lisp Concepts

conditional operators if, cond, when, until
logical operators and, or, not, unless
mappings mapcar, maplist
arrays
structures
lambda functions
Macro

17
A simple example

gt(let ((sum 0))
(mapcar '(lambda (x)
(incf sum ( x x)))
'(1 2 3 4))
sum)
gt30
(Not working if you define a separate function
like this
(defun aaa (x)
(incf sum ( x x)))
(let ((sum 0))
(mapcar aaa (1 2 3 4))
sum)

18
Macro

Different concept from Macro in C. In C, its
just stupid replacing some strings.
In Lisp, Macro is a scheme to generate source
code.
Two phrases Expand Macro, then compile all the
functions.
(defun square-code (x)
( ,x ,x))
(defmacro foo (x)
(square-code x))

(defun foo (x) (square-code x))
Output??
19
When to use macro?

When to use Macro?
Macro is powerful if there are some frequent
patterns in the source code.
Never use a macro instead of a function for
efficiency reasons

20
Suggested programming style

Write short functions, where each function
provides a single, well-defined operation
Use proper indentation
Program idea with recursion
Top-down approach with abstraction

21
Useful commands for lisp in a box