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The TeachScheme! Project Adelphi University Brown University Northeastern University University of Chicago University of Utah Worcester Polytechnic Institute

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The Revolution Two principles: Emphasis on correctness over efficiency (ie, focus on program design) Shift away from machine details

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Whats Wrong with Machine-Oriented Languages? Make students waste time on unimportant and uninteresting details Force students to confront issues they are not prepared for and... machine arithmetic, pointers and memory addresses, even i/o

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What Computer Science is Not About The computer! Just as biology isnt microscope science and writing isnt pen science...

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Whats This About Program Design?

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Why Am I Here? The TeachScheme! Project: Outreach program hosted by six universities Specially designed for high schools Provides all material -- books, software, etc -- free of charge

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What Teachers Experience

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K.I.S.S. Keep It Simple Syntactically C++/Pascal 10% Problem-solving vs 90% Syntax Scheme 90% Problem-solving vs 10% Syntax

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The Golden Rule of Scheme Syntax ( )OperationList-of-Arguments or ( Operation Arg 1 )

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The Golden Rule of Scheme Syntax ( )OperationList-of-Arguments or ( Operation Arg 1 Arg 2 )

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The Golden Rule of Scheme Syntax ( )OperationList-of-Arguments or ( Operation Arg 1 Arg 2... Arg n )

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An Example From Arithmetic 4 + 5 ( Operation Arg 1 Arg 2 )

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4 + 5 ( Operation Arg 1 Arg 2 ) ( ) Example #1 (contd)

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4 + 5 ( Operation Arg 1 Arg 2 ) ( + ) Example #1 (contd)

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4 + 5 ( Operation Arg 1 Arg 2 ) ( + 4 ) Example #1 (contd)

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4 + 5 ( Operation Arg 1 Arg 2 ) ( + 4 5 ) Example #1 (contd)

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4 + 5 ( + 4 5 ) Example #1 (contd)

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Another Arithmetic Example ( 4 + 5 ) · 6

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( ) Example #2 (contd)

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( 4 + 5 ) · 6 ( * ) Example #2 (contd)

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( 4 + 5 ) · 6 ( * ( + 4 5 ) ) Example #2 (contd)

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( 4 + 5 ) · 6 ( * ( + 4 5 ) 6 ) Example #2 (contd)

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( 4 + 5 ) · 6 ( * ( + 4 5 ) 6 ) Example #2 (contd)

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An Example From Algebra 4 + 5 f ( x ) = x + 5

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 )

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 ) ( )

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 ) ( define )

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 ) ( function-name input-name ) ( f x )

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 ) ( define ( f x ) )

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 ) ( output-rule ) ( + x 5 )

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Example #3 (contd) f ( x ) = x + 5 ( Operation Arg 1 Arg 2 ) ( define ( f x ) ( + x 5 ) )

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Example #3 (contd) f ( x ) = x + 5 ( define ( f x ) ( + x 5 ) )

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Algebra vs Scheme vs Pascal Program (Input, Output) ; Program f (Input, Output) ;Var x : Integer ; x : Integer ;Begin Readln ; Readln ( x ) ; Writeln ( ) Writeln ( x + 5 ) End. Pascal f (x) = x + 5 Algebra ( define ( define ( f x ) ( ) ) ( + x 5 ) ) Scheme

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Design

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D 3 : Data Drive Design ( A Non-Numeric Example) Consider program guest, which determines whether a friends name is in a partys invitation list.

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Is Mathilde In The List? No Mathilde... John... Yes Look in the Rest of the List

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No Mathilde... Sherry... Yes Look in the Rest of the List Is Mathilde In The Rest of the List?

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Pattern To Algebra

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guest ( name, list ) = Algebra

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guest ( name, list ) = Algebra

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guest ( name, list ) = if list is empty Algebra

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guest ( name, list ) = noif list is empty Algebra

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guest ( name, list ) = noif list is empty if name = first ( list ) Algebra

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guest ( name, list ) = noif list is empty yesif name = first ( list ) Algebra

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guest ( name, list ) = noif list is empty yesif name = first ( list ) otherwise Algebra

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guest ( name, list ) = noif list is empty yesif name = first ( list ) guest ( name, rest ( list ))otherwise Algebra

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Scheme ( define ( guest name list ) ) guest ( name, list ) = Algebra

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Scheme ( define ( guest name list ) ) guest ( name, list ) = Algebra

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Scheme ( define ( guest name list ) ( cond )) guest ( name, list ) = Algebra

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guest ( name, list ) = if list is empty if name = first ( list ) otherwise Algebra Scheme ( define ( guest name list ) ( cond ))

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Scheme ( define ( guest name list ) ( cond ( ) ( ) )) guest ( name, list ) = if list is empty if name = first ( list ) otherwise Algebra

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Scheme ( define ( guest name list ) ( cond ( ( empty? list ) ) ( ( equal? name ( first list )) ) ( else ) )) guest ( name, list ) = if list is empty if name = first ( list ) otherwise Algebra

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Scheme ( define ( guest name list ) ( cond ( ( empty? list ) no ) ( ( equal? name ( first list )) yes ) ( else ( guest name ( rest list )) ) )) guest ( name, list ) = noif list is empty yesif name = first ( list ) guest ( name, rest ( list ))otherwise Algebra

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Did You Notice?

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Scheme Algebra ( define ( guest name list ) ( cond ( ( empty? list ) no ) ( ( equal? name ( first list )) yes ) ( else ( guest name ( rest list )) ) )) guest ( name, list ) = noif list is empty yesif name = first ( list ) guest ( name, rest ( list ))otherwise

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Recursion Is Natural

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Comparisons

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Program NameOnList (Input, Output) ; Type ListType = ^NodeType; NodeType = Record First : String; Rest : ListType End; Var List : ListType; Name : String; Procedure GetList (Var List: ListType);... Function Guest (Name : String; List : ListType) : String; Begin If List = nil Then Guest := no Else If Name = List^.First Then Guest := yes Else Guest := Guest ( Name, List^.Rest) End; Begin Readln ( Name ); GetList ( List ); Writeln (Guest ( Name, List ) ) End. Pascal

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Program NameOnList (Input, Output) ; Type ListType = ^NodeType; NodeType = Record First : String; Rest : ListType End; Var List : ListType; Name : String; Procedure GetList (Var List: ListType);... Function Member (Name : String; List : ListType) : String; Begin If List = nil Then Member := no Else If Name = List^.First Then Member := yes Else Member := Member ( Name, List^.Rest) End; Begin Readln ( Name ); GetList ( List ); Writeln (Member ( Name, List ) ) End. Pascal ( define ( guest name list ) ( cond ( ( empty? list no ) ( ( equal? name ( first list )) yes ) ( else ( guest name ( rest list )) ) )) Scheme

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#include #include typedef struct listCell * list; struct listCell { int first; int first; list rest; list rest;}; bool guest (int x, list l) { if (l == NULL) if (l == NULL) return false; return false; else if (x == (l -> first)) else if (x == (l -> first)) return true; return true; else else return guest (x, l -> rest); return guest (x, l -> rest);} int main (int argc, char ** argv) { list l1, l2, l3 = NULL; int x; list l1, l2, l3 = NULL; int x; l1 = (list) malloc (sizeof (struct listCell)); l1 = (list) malloc (sizeof (struct listCell)); l2 = (list) malloc (sizeof (struct listCell)); l2 = (list) malloc (sizeof (struct listCell)); l2 -> first = 3; l2 -> rest = l3; l2 -> first = 3; l2 -> rest = l3; l1 -> first = 2; l1 -> rest = l2; l1 -> first = 2; l1 -> rest = l2; scanf ("%d", &x); scanf ("%d", &x); printf ("%d\n", member (x, l1)); printf ("%d\n", member (x, l1));} C or C++ ( define ( guest name list ) ( cond ( ( empty? list no ) ( ( equal? name ( first list )) yes ) ( else ( guest name ( rest list )) ) )) Scheme

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Principles of Program Design K.I.S.S.: Keep It Simple Syntactically Recursion Is Natural D 3 : Data Drive Design

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The Ping-Pong Game 9th Graders With Algebra I 12 Weeks of Scheme

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Curriculum Comparison introduction syntax Turbo Pascal, i/o numbers, strings simple arithmetic text files conditionals procedures, stubs algebra, functions conditionals design recipes symbols linked lists structures, records graphics lists containing lists

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The Programming Environment Salient DrScheme features: interactive evaluation immediate error-reporting with source highlighting language presented as a sequence of increasingly complex layers

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Putting it in Context

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What a University Saw Universities like Rice admit some of the best students in the nation; yet, the students cannot develop a program systematically separate problem solving from machine details explain why a program works (or doesnt)

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What the ETS Wishes You Didnt Know (~1998)

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Conclusion Computer science education is undergoing a revolution TeachScheme! is at the forefront Schools and universities must collaborate to reap the benefits

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What We Offer Textbook (How to Design Programs) DrScheme programming environment Teachers guide Programming environment guide Exercises and solution sets Miscellany: help, summer course, etc All available for free!

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Web Information See http:/www.teach-scheme.org/ for information about the project, especially the free summer courses

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