Introduc)on. Tristan Naumann. Sahar Hasan. Steve Hehl. Brian Lu

Transcription

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2 Introduc)on Tristan Naumann Sahar Hasan Steve Hehl Brian Lu

3 Introduc)on Friendly Interac)ve Recursion Educator (FIRE) Recursion is one of the most difficult topics for novice programmers to understand Teach through interac)ve visualiza)on: users see the progression of recursive calls and the propaga)on of results back to the original call Simple syntax: more )me learning recursion, less )me debugging code

4 Syntax An example using the Fibonacci numbers: define recursive int fibonacci (int n): base: {n == 0} 0 {n == 1} 1 recursive: { } fibonacci(n 1) + fibonacci(n 2)

5 Syntax An example using the Fibonacci numbers: define recursive int fibonacci (int n): Keywords signifying the base: {n == 0} 0 beginning of the {n == 1} 1 recursive func)on defini)on recursive: { } fibonacci(n 1) + fibonacci(n 2)

6 Syntax An example using the Fibonacci numbers: define recursive int fibonacci (int n): base: {n == 0} 0 {n == 1} 1 Return data type recursive: { } fibonacci(n 1) + fibonacci(n 2)

7 Syntax An example using the Fibonacci numbers: define recursive int fibonacci (int n): base: {n == 0} 0 {n == 1} 1 Func)on name recursive: { } fibonacci(n 1) + fibonacci(n 2)

8 Syntax An example using the Fibonacci numbers: define recursive int fibonacci (int n): base: {n == 0} 0 {n == 1} 1 Comma delimited parameter list recursive: { } fibonacci(n 1) + fibonacci(n 2)

9 Syntax An example using the Fibonacci numbers: define recursive int fibonacci (int n): base: {n == 0} 0 {n == 1} 1 Indented block of base cases of the form: {condi)on} returnval recursive: { } fibonacci(n 1) + fibonacci(n 2)

10 Syntax An example using the Fibonacci numbers: Indented block of the implicitly returned base: recursive case: {n == 0} 0 { } recursivecall {n == 1} 1 define recursive int fibonacci (int n): recursive: { } fibonacci(n 1) + fibonacci(n 2)

11 Syntax Other syntac)cal features Watch block: comma delimited list of variables whose values the user wishes to track Explicit condi)onals (if/else) and loops (for, while) Built in func)ons for lists Print statements and comments

12 Syntax Whitespacing FIRE uses Python based whitespace indenta)on for block delimi)ng instead of curly braces Indenta)on follows certain statements and signifies the beginning of a block Dedenta)on signifies the end of a block

13 Syntax Advantages Makes code more readable Easier to write because dedents are automa)cally matched to indents for the user Disadvantages Harder to implement because indenta)on levels must be tracked using a stack as opposed to simply detec)ng matching braces

14 Syntax Stack implementa)on notes from Python For each line, compare indenta)on level to top of stack (ini)ally contains one pushed 0) If equal, do nothing If larger, push onto stack and issue INDENT If smaller, pop all numbers on stack that are larger and issue DEDENT for each On EOF, issue remaining DEDENTS

15 Output Screenshot of a recursive call step

16 Output Screenshot of a return value propaga)ng back

17 System Architecture Overview User file ANTLR InputStream Lexer WSFilter Common TokenStream Characters Tokens Error checking + scoping Parser String Template Fire.java Java compiler Parsed Fire.class JVM GUI package Backend Frontend

18 System Architecture Overview User file ANTLR InputStream Lexer WSFilter Common TokenStream Characters Tokens Error checking + scoping Parser String Template Fire.java Java compiler Parsed Fire.class JVM GUI package Backend Frontend

19 System Architecture Overview User file ANTLR InputStream Lexer WSFilter Common TokenStream Characters Tokens Error checking + scoping Parser String Template Fire.java Java compiler Parsed Fire.class JVM GUI package Backend Frontend

20 System Architecture Overview User file ANTLR InputStream Lexer WSFilter Common TokenStream Characters Tokens Error checking + scoping Parser String Template Fire.java Java compiler Parsed Fire.class JVM GUI package Backend Frontend

21 System Architecture Overview User file ANTLR InputStream Lexer WSFilter Common TokenStream Characters Tokens Error checking + scoping Parser String Template Fire.java Java compiler Parsed Fire.class JVM GUI package Backend Frontend

22 System Architecture Development tools Eclipse Ganymede + Subeclipse ANTLR v3 + StringTemplate 3.2 Java SE 6 + Swing Management tools Google Code Google Docs

23 Tes)ng Mul) stage tes)ng approach Unit tes)ng whitespacing Unit tes)ng grammar produc)on rules User tes)ng full examples

24 Tes)ng Whitespace tes)ng Source (fibonacci.fire) define recursive int fibonacci (int n): base: Token stream output <DEFINE> <WS> <RECURSIVE> <WS> <TINT> <WS> <NAME> <WS> <LPAREN> <TINT> <WS> <NAME> <RPAREN> <COLON> <NEWLINE> <INDENT> <BASE> <COLON> <NEWLINE> {n == 0} 0 <INDENT> <LCURLY> <NAME> <WS> <EQ> <WS> <INT> <RCURLY> <WS> <INT> <NEWLINE> {n == 1} 1 <LCURLY> <NAME> <WS> <EQ> <WS> <INT> <RCURLY> <WS> <INT> <NEWLINE> recursive: <DEDENT> <RECURSIVE> <COLON> <NEWLINE> { } fibonacci(n 1) + fibonacci(n 2) <INDENT> <LCURLY> <WS> <RCURLY> <WS> <NAME> <LPAREN> <NAME> <MINUS> <INT> <RPAREN> <WS> <PLUS> <WS> <NAME> <LPAREN> <NAME> <MINUS> <INT> <RPAREN> <NEWLINE> <DEDENT> <DEDENT>

25 Tes)ng Grammar produc)on tes)ng FIRE Program Inputs Java target code Tester: Translate program to Java and compare to target code Equivalent (PASS) Output result of comparison Not equivalent (FAIL)

26 Conclusion Lessons learned User friendly languages are harder to write and test Python as a reference language: not everything translates well to Java Future improvements Support for corecusion Mul)ple types of output

27 Conclusion Key benefits Supports many common recursions of mul)ple types Shallow learning curve; code is both easy to write and understand Automated instrumenta)on of the code and visual output

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