CS4005 Project 1 Implementation of a Lexer Solved

Description

1. Problem:

In this assignment you are requested to use the tool ANTLR to write a scanner for a small language Cactus. The language Cactus contains the following categories of token types:

 

1. An identifier is a sequence of letters and digits; the first character must be a letter. The underscore ‘_’ counts as a letter. All identifiers are returned as a single token type.
2. The following identifiers are reserved for use as keywords, and may not be used otherwise:

else fi if int main return while read write Each keyword is returned as a distinct token type.

3. An integer constant consists of a sequence of digits. All integer constants are returned as a single token type.
4. Operators include

+ – * / % == != > >= < <= && || ! = ( ) { } ; Each operator is returned as a distinct token type.

5. Blanks, tabs, and newlines are ignored except as they serve to separate tokens.
6. Comments are ignored except as they serve to separate tokens. The characters /* introduces a comment, which terminates with the characters */. Comments do not nest.

 

You can follow the following steps:

1. Edit a grammar Cactus.g4 that contains the regular expressions for each of the token types as follows.

 

// The grammar for Cactus language grammar Cactus;

 

// Parser rules

token : (ELSE | … | ID | CONST | ADD | … )*

 

// lexer rules

ELSE : ‘else’

…

ID : …

CONST : …

ADD : ‘+’

…

WHITESPACE : …

COMMENT : …

 

2. Use the ANTLR tool to generate the scanner and parser java code.

 

$antlr4 Cactus.g4

 

3. Compile the generated java code.

 

$javac Cactus*.java

 

4. Use the ANTLR tool to execute the scanner and parser.

 

$grun Cactus token -tree

 

If the input is as follows:

 

/* A program to sum 1 to n */ main()

{ int n; int s; int i;

 

read n;

if ( n < 1 ) {

write -1;       return;    } else {       s = 0;

} fi    i = 1;     while ( i <= n) {       s = s + i;       i = i + 1;

} write s;

return;

}

 

The output should be

 

(token main ( ) { int n ; int s ; int i ; read n ; if ( n < 1 ) { write – 1 ; return ; } else { s = 0 ; } fi i = 1 ; while ( i <= n ) { s = s + i ; i = i + 1 ; } write s ; return ; })

 

2. Handing in your program:

To turn in the assignment, upload a compressed file proj1 containing Cactus.g4, Cactus.tokens, Cactus*.java, and Cactus*.class to eCourse2 site.

 

4. Grading

The grading is based on the correctness of your program. The correctness will be tested by a number of test cases designed by the instructor and teaching assistants.