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.
