Entire Site
Free Trial
Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
- Create BookmarkCreate Bookmark
- Create Note or TagCreate Note or Tag
- DownloadDownload
- PrintPrint
Chapter 19. Parsing > Exercises
Exercises
| 1. | Add / and % operations to the arithmetic expression evaluator. |
| 2. | Add a ^ operator to the arithmetic expression evaluator. As in mathematics, ^ should have a higher precedence than multiplication, and it should be right-associative. That is, 4^2^3 should be 4^(2^3), or 65536. |
| 3. | Write a parser that parses a list of integers (such as (1, 23, -79)) into a List[Int]. |
| 4. | Write a parser that can parse date and time expressions in ISO 8601. Your parser should return a java.util.Date object. |
| 5. | Write a parser that parses a subset of XML. Handle tags of the form <ident> ... </ident> or <ident/>. Tags can be nested. Handle attributes inside tags. Attribute values can be delimited by single or double quotes. You don’t need to deal with character data (that is, text inside tags or CDATA sections). Your parser should return a Scala XML Elem value. The challenge is to reject mismatched tags. Hint: into, accept. |
| 6. | Assume that the parser in Section 19.5, “Generating Parse Trees,” on page 275 is completed with
class ExprParser extends RegexParsers {
def expr: Parser[Expr] = (term ~ opt(("+" | "-") ~ expr)) ^^ {
case a ~ None => a
case a ~ Some(op ~ b) => Operator(op, a, b)
}
...
}Unfortunately, this parser computes an incorrect expression tree—operators with the same precedence are evaluated right-to-left. Modify the parser so that the expression tree is correct. For example, 3-4-5 should yield an Operator("-", Operator("-", 3, 4), 5). |
| 7. | Suppose in Section 19.6, “Avoiding Left Recursion,” on page 276, we first parse an expr into a list of ~ with operations and values:
def expr: Parser[Int] = term ~ rep(("+" | "-") ~ term) ^^ {...}To evaluate the result, we need to compute ((t0 ± t1) ± t2) ± . . . Implement this computation as a fold (see Chapter 13). |
| 8. | Add variables and assignment to the calculator program. Variables are created when they are first used. Uninitialized variables are zero. To print a value, assign it to the special variable out. |
| 9. | Extend the preceding exercise into a parser for a programming language that has variable assignments, Boolean expressions, and if/else and while statements. |
| 10. | Add function definitions to the programming language of the preceding exercise. |
