[Solved] CS4005 Project 1 Implementation of a Lexer

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.