Logo -- A Language for Learning

Logo -- A Language for Learning Liping Cai 11/21/2005

Agenda • What is Logo? • History • Syntax and Example • Demo • Reference

What is Logo? • Designed to manipulate language – Words and Sentences. • Designed to introduce children to programming concepts • Intended to be easy to learn, easy to use, easy to read, but also powerful and able to cope with complex problems. • Features: modularity, extensibility, interactivity, and flexibility • Areas of Application: Graphics (Turtle Graphics), Use with Language, Making Music

History • The first version of Logo is created in 1967 by Seymour Papert and his team. • Throughout the 1970s Logo was incubating at MIT and a few other research sites. • Widespread use of Logo began with the advent of personal computers during the late 1970s. • the Logo boom is in the early 1980s but Logo did not become popular among applications programmers. • Over the past few years there has been a flurry of new Logo development accompanied by renewed public awareness and enthusiasm. • MicroWorlds. Released in 1993 by LCSI. MicroWorlds includes many extra-Logo features - drawing tools, a shape editor, a melody maker, the ability to import graphics and sounds - that work along with Logo to support the creation of multimedia projects, games, and simulations. • Logo has also been incorporated into HyperStudio, the widely popular multimedia program for Macintosh and Windows from Roger Wagner Productions.

Get to Know Logo • Turtle: Cursor for Logo -- set position of the logo: Turtle Screen Positions using <Setxy horizontal vertical> • Technical Terms: -- instruction: is what you type to Logo to tell it to do something. Print 17 is an example of an instruction. -- procedure: is a small piece of code that performs a single task ;Procedures are invoked by instructions. Print is a procedure. -- command: is a procedure that does not output a value but instead has some effect such as printing something on the screen, moving a turtle, or making a sound. Print is a command; -- operation: is a procedure that computes a value and outputs it. Sum and product are operations.

Simple Commands • Forward 100 - moves the turtle forward 100 unit • Back 50 - moves the turtle back 50 units • Right 45 - turns the turtle 45 degrees to the right • Left 90 - turns the turtle 90 degrees to the left • Home - Returns the turtle to its origin • ClearSceen - Erases the screen • repeat 4 [FD 100 RT 90] – draw a square • Print “hello – print Hello on the screen

primitive operations • Sum: Print Sum 2 3 – 5 • First: Print first “Hello – H; Print first [How are you?] – How • Butfrist: Print butfirst “hello – ello; Print butfirst [how are you?] – are you? • Item: Print item 3 “ how – w; Print item 3 [How are you] – you • Sentence: print sentence "hello "goodbye -- hello goodbye print sentence [this is] [a test] -- this is a test; print sentence "this [is one too] -- this is one too; print sentence [] [list of words] – list of words; • Word: print word "now "here – nowhere; print word "this [is a test] -- word doesn't like [is a test] as input • List: print list [this is] [a test] -- [this is] [a test]; print list "this [is one too] -- this [is one too]; print list [] [list of words] -- [] [list of words] ;

Define Procedures & Variables: • To define a procedure: To procedure …. Statements End • To define a variable: MAKE "<variableName> <value> eg make "size 10. In this example the variable called "size" will now have a value of ten. make "position {1 2 3 4 5 6 7 8 9} -- make an array • Using variable in Procedure: colon(:) in front of variable name. to numberingmake "size 10label :sizeend

Predicates & Operator: • A predicate is an operation whose output is always either the word true or the word false. Listp -- return true if input is a list, false if not. print wordp "hello – true; print wordp [hello] – false print emptyp []-- true; print emptyp 0 –false print equalp 3 3.0-- true; print equalp "hello [hello]--false • Define custom Predicates: to vowelp :letter output memberp :letter [a e i o u] end print vowelp “e – true; print vowelp “h – false. • Operators: + - * /

Conditional Commands & Iteration • If: if equalp 2 1+1 [print "Yup.] – Yup. • ifelse: ifelse 4 = 2+2 [print "Yup.] [print "Nope.] -- Yup • iftrue and iffalse : make "variable1 27make "variable2 33test :variable1 = :variable2iftrue [print [The values are the same.]]ifffalse [print [The values are different.]] --The values are different. • Until, while : until [condition][action]; while [condition][action] until [:count > 10][print :count make "count :count + 1] -- 1 2 3 4 5 6 7 8 9 10 where [:count < 10][print :count make "count :count + 1] -- 1 2 3 4 5 6 7 8 9 • Do.until, do.while : do.until [action][condition] do.while [action][condition] do.until [print :count make "count :count + 1][:count > 10] --1 2 3 4 5 6 7 8 9 10 do.while [print :count make "count :count + 1][:count < 10]--1 2 3 4 5 6 7 8 9

Conditional Commands & Iteration (Continued) • For: for [variable_name starting_value limit_value, steps] for [number 4 7] [print :number] – 4 5 6 7 for [value 4 11 3] [print :value] -- 4 7 1 0 • Foreach : take each element in the list foreach [chocolate [rum raisin] pumpkin] [print sentence [I like] ?] -- I like chocolate I like rum raisin I like pumpkin • Map : collect the results of doing this for each of those • Macro: Berkeley Logo includes this mechanism, no other version has Macro, Like Lisp.

Recursion(Graphic Example) to tree :size if :size < 5 [forward :size back :size stop] forward :size/3 left 30 tree :size*2/3 right 30 forward :size/6 right 25 tree :size/2 left 25 forward :size/3 right 25 tree :size/2 left 25 forward :size/6 back :size End Tree 100

References • http://www.cs.berkeley.edu/~bh/v1-toc2.html Symbolic Computing, a Logo programming text that concentrates on natural language processing rather than the graphics most people associate with Logo. • http://www.cs.berkeley.edu/~bh/v2-toc2.html Advanced Techniques, in which discussions of more advanced Logo features alternate with sample projects using those features, with commentary on the structure and style of each. • http://www.cs.berkeley.edu/~bh/v3-toc2.html Beyond Programming, brief introductions to six college-level computer science topics.

More References • http://library.advanced.org/18446/eindex.shtml • Star Logo Home Page http://el.www.media.mit.edu/groups/el/projects/starlogo/ • The Logo Foundation http://lcs.www.media.mit.edu/groups/logo-foundation/ • Download a FREE version of MSW Logo http://www.softronix.com • Links to all sorts of Logo Resources http://lcs.www.media.mit.edu/groups/logo-foundation/links.html

Logo -- A Language for Learning