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.

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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)

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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.

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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)

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• 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.

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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

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• 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.,

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Conditional Constructs

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

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

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Creating Variables

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

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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.
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Other Important Lisp Concepts

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

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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)

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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??
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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

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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

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Useful commands for lisp in a box

• Ctrl-c Ctrl-z Return to the interpreter
• Ctrl-c Ctrl-c Compile a function
• Ctrl-c Ctrl-k Compile and load a file
• Ctrl-c Ctrl-d Ask for the description
• Ctrl-c Ctrl-h hyperspec description
• Ctrl-c Ctrl-q complete all the parenthesis
• A short flash for programming in slime.
• Other basic commands for emacs

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Useful keybindings

• Switch with ()
• Switch command Ctrl-b and CtrlMetab
• You can customize your settings by adding stuff
  in 99init.el
• http//www.cliki.net/Editing20Lisp20Code20with
  20Emacs

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How to deal with problems

• I am not a superman to solve all your problems ?
• Where you can ask
• Newsgroup comp.lang.lisp
• Search Google.
• Check the documentation of specified functions.
• Discuss with each other

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• Lisp is a language for smart
  people. Have Fun with Lisp?
• Questions?