201506 CSE340 Lecture 13

CSE340 - Principles of Programming Languages Lecture 13:

Parsing Techniques I Javier Gonzalez-Sanchez [email protected] BYENG M1-38 Office Hours: By appointment

Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 2

1 •  Understand de provided source code

(3 rules)

2 •  Program the rules PROGRAM, BODY, EXPRESSION, X, Y, R, E, C

(11 rules)

3 •  Program the full set of rules in the grammar

(16 rules)

4 •  Report syntactical errors (one error and stop)

PANIC MODE

5 •  Implement error synchronization

ERROR RECOVERY

Assignment 2


Programming Assignment 2

Level 4

Handling Syntactical Errors (part 1): Error messages


Assignment 2 | Grammar

<PROGRAM> à '{' <BODY> '}’ <BODY> à {<PRINT>';'|<ASSIGNMENT>';'|<VARIABLE>';’|<WHILE>|<IF>|<RETURN>';'} <ASSIGNMENT> à identifier '=' <EXPRESSION> <VARIABLE> à ('int'|'float'|'boolean'|'char’|'string'|'void')identifier

<WHILE> à 'while' '(' <EXPRESSION> ')' <PROGRAM> <IF> à 'if' '(' <EXPRESSION> ')' <PROGRAM> ['else' <PROGRAM>] <RETURN> à 'return' <PRINT> à ’print’ ‘(‘ <EXPRESSION> ‘)’ <EXPRESSION> à <X> {'|' <X>}

<X> à <Y> {'&' <Y>} <Y> à ['!'] <R> <R> à <E> {('>'|'<'|'=='|'!=') <E>} <E> à <A> {(’+'|'-’) <A>} <A> à <B> {('*'|'/') <B>} <B> à ['-'] <C> <C> à integer | octal | hexadecimal | binary | true | false |

string | char | float | identifier|'(' <EXPRESSION> ')'


Error Synchronization

PROGRAM

BODY

ASSIGNMENT

VARIABLE

WHILE

IF

RETURN

PRINT

C

EXPRESSION

X

Y

R

E

A

B


Assignment 2

{}

Input:

Build successful

Output:


Assignment 2

{

hello word }

Input:

Line 2: expected =

Line 2: expected ;

Output:


Assignment 2

{

int x int

int int x;

}

Input:

Line 2: expected ;

Line 3: expected identifier Line 3: expected ;

Line 4: expected identifier

Output:


Assignment 2

{ x = a;

x = 0x36AW;

x = ((((((((((y)))))))))); x = (5+(4-(3+(5+5/(2+(3+(1+(77+(1-(y)))))))))) + “hello” + ‘q’;

if (a < b) {} else {} if (a < b) { if (a < b) { } else { } } }

Input:

Line 3: expected value, identifier or (

Output:


Parser | Error Points

PROGRAM

Line N: expected {

Line N: expected }



Line N: expected ;

BODY

Line N: expected identifier or keyword



ASSIGNMENT

Line N: expected =



VARIABLE

Line N: expected identifier



WHILE

Line N: expected (

Line N: expected )



IF

Line N: expected ( Line N: expected )



RETURN



PRINT

Line N: expected ( Line N: expected )



EXPRESSION

X

Y

R

E

A

B


Parser | Error Points C

Line N: expected value, identifier or (

Line N: expected )


Assignment 2 public static void error(int err) { int n = tokens.get(currentToken).getLine();

switch (err) {

case 1: gui.writeConsole("Line” + n + ": expected {”); break; case 2: gui.writeConsole("Line” + n + ": expected }”); break; case 3: gui.writeConsole("Line” + n + ": expected ;”); break; case 4:

gui.writeConsole("Line” +n+": expected identifier or keyword”); break; case 5:

gui.writeConsole("Line” +n+": expected =”); break; case 6: gui.writeConsole("Line” +n+": expected identifier”); break; case 7: gui.writeConsole("Line” +n+": expected )”); break; case 8:

gui.writeConsole("Line” +n+": expected (”); break; case 9:

gui.writeConsole("Line” +n+": expected value, identifier, (”); break;

}

}


Updates

1. In Gui.java: make the method writeConsole public

2. In Gui.java: add this as a second parameter for the method Parser.run()

3. In Parser.java: add the attribute gui (line 15) add a second parameter to the method run (line 17) initialize gui (line 18)


Homework

Programming Assignment #2

CSE340 - Principles of Programming Languages

Javier Gonzalez-Sanchez

[email protected] Summer 2015

Disclaimer. These slides can only be used as study material for the class CSE340 at ASU. They cannot be distributed or used for another purpose.

201506 CSE340 Lecture 13

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