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Written Assignment 3
This assignment asks you to prepare written answers to questions on LL and LR parsers. Each of the questions has a short answer. You may discuss this assignment with other students and work on the problems together. However, your write-up should be your own individual work.
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- Use left-factoring and/or elimination of left recursion to convert the following grammars into LL(1) grammars. You may assume that these grammars are unambiguous.
(a)
E โ E + T | T | E! T โ int | (E)
(b)
L โ X | L, X X โ int | string | (L)
(c)
P โ P H 4 U | p H โ h U โ u | u P
- Consider the following grammar fragment for a familiar syntax:
U RL โ P ROT O : / / HOST / F ILE
P ROT O โ http P ROT O โ f tp HOST โ id I I โ I โ. HOST F ILE โ id G G โ G โ. F ILE G โ / F ILE
The nonterminals are U RL, P ROT O, HOST , I, F ILE and G.
(a) Left-factor this grammar. (b) Give the First and Follow sets for each nonterminal in the gram- mar obtained in part (a). (c) Using this information, construct an LL parsing table for the grammar obtained in part (a). (d) Suppose we generated an LL parser for the grammar using the table you constructed. What would go wrong if it tried to parse the following input string?
f tp : //id.id/id./id..id (That is, when we get an error, how much of the input string has been consumed, and what is the parser trying to do?)
- Consider the following LR(1) grammar:
S โ A
A โ A + A | B + + (Each โ+โ is a separate token.) B โ y
