public Parser(Scanner s)
{
scanner = s;
nil = new Nil();
tr = new BoolLit(true);
fa = new BoolLit(false);
}
//parses grammar for exp ->
public Node parseExp()
{
Token tok;
tok = scanner.getNextToken();
//checks for end of file
if (tok == null)
{
Nil retNil = nilPoint;
return(retNil);
}
//checks for case of left parenthesis
if (tok.getType() == TokenType.LPAREN)
{
return(parseRest(true));
}
//checks for case of false constant
else if (tok.getType() == TokenType.FALSE)
{
BoolLit ret = fBool;
return(ret);
}
//checks for case of true constant
else if (tok.getType() == TokenType.TRUE)
{
BoolLit ret = tBool;
return(ret);
}
//checks for case of QUOTE symbol
else if (tok.getType() == TokenType.QUOTE)
{
return(new Cons(new Ident("quote"), new Cons(parseExp(), new Nil()), true));
}
//checks for case int constant
else if (tok.getType() == TokenType.INT)
{
return(new IntLit(tok.getIntVal()));
}
//checks for case of string constant
else if (tok.getType() == TokenType.STRING)
{
return(new StringLit(tok.getStringVal()));
}
//checks for case of identifier
else if (tok.getType() == TokenType.IDENT)
{
return(new Ident(tok.getName()));
}
return(null);
}
