Groundhog's Day

BNF

A set of symbols including:

terminals
non terminals (can be replaced by other symbols)
a special symbol called the start symbol

a set of rules for producing strings in the language.

Postal Example:

<postal-address> ::= <name-part> <street-address> <zip-part>

 <personal-part> ::= <name> | <initial> "."

 <name-part> ::= <personal-part> <last-name> [<jr-part>] <EOL>
	       | <personal-part> <name-part>

 <street-address> ::= [<apt>] <house-num> <street-name> <EOL>

 <zip-part> ::= <town-name> "," <state-code> <ZIP-code> <EOL>

Grammar for a simple assignment statements:

<assign> -> <id> = <expr>
<id> -> A | B | C
<expr> -> <ID> + <expr>
          | <id> * <expr>
          | (<expr>)
          | <id>


A = B * (A + C)

This grammar is Ambiguous, why?
A = B + C * A
Derive the tree

Fix the OP:

<assign> -> <id> = <expr>
<id> -> A | B | C
<expr> -> <ID> + <term>
              | <term>
<term> -> <term> * <factor>
              | <factor>
<factor> -> (<expr>)
	      |<id>

Now derive the tree

BNF rules for Java

Non-recursive

Recursive

Left recursive
Right recursive

Whitespace -

FORTRAN treated blanks as completely insignificant in the body of a statement. This could sometimes be convenient, e.g., to make numbers and variable names more readable.
Two Equivalent Forms
HIVAL = 14713678923
HI VAL = 14 713 678 923
However, ignoring blanks can sometimes cause problems. For example, consider the looping statement:

DO 3 I = 1,3

Suppose this were mistakenly coded with a period instead of a comma.

Two Equivalent Forms

DO 3 I = 1.3 DO3I = 1.3

The interpretation would be as a variable assignment.
Unfortunately, exactly this kind of error occurred in the control program for a Mariner spacecraft to Venus, resulting in its loss. (Annals of the History of Computing, 1984, 6(1), page 6).

Compilers
Comments - two basic conventions (plus java docs comments)
Python

Some of Rocky's Ross's Research, Webworks a animated tool for showing Context Free Grammars

Sample Questions:

Consider the grammar given below

<pop> ::= [ <bop> , <pop> ] | <bop>
<bop> ::= <boop> | ( <pop> )
<boop> ::= x | y | z

(a)What are the nonterminal symbols?
(b) What are the terminal symbols?
(c) What is the start symbol?
(d) Draw a parse tree for the sentence (x).
Given the following grammar in BNF:

<assign> -> <id> = <expr>
<id> -> A | B | C
Given the following grammar in BNF:

S -> A B C
A -> aA | a
B -> bB | b
C -> cC | c

What is the shortest string that belongs to the grammar?
Describe, in English, the language defined by the following grammar in BNF

<S> -> <A> <B> <C>
<A> -> a <A> | a
<B> -> b <B> | b
<C> -> c <C> | c
Write a BNF description of the Boolean expression of Java, including the three operators &&, ||, and !, and the relational expressions with operators = =, !=, <, <=, >=, >.