Grammars

















How does the parser process the tokens from the following code?

How does the parser know if the input is valid code?
What notation is commonly used to specify syntax?

    void quote() {

	print(

	    "To err is human, but to really foul things up you need a computer." + 
	    " - Paul Ehrlich"

	);

    }


















Here's a Grammar for simple expressions.

	E -> (E + E)
	E -> (E * E)
	E -> 1
	E -> x
	E -> y


Show the steps that generate the expression.

	(x * (1 + y))


















Classwork
You may work with a partner.

Use the Grammar to show the steps that generate the expression.

	x * 1 + y

	E -> E + T | T
	T -> T * F | F
	F -> 1 | x | y
















Classwork
You may work with a partner.

Use the Grammar to show the steps that generate the sentence.

	the tree eats loudly

	sentence -> noun-phrase verb-phrase
	noun-phrase -> article noun
	verb-phrase -> verb adverb
	article -> a
	article -> the
	noun -> tree
	noun -> monkey
	verb -> eats
	verb -> talks
	adverb -> wildly
	adverb -> loudly


















Grammar Terminology


What's a Production (Rule)?

What's a Terminal?

What's a Nonterminal (Variable)?

What's the Start Symbol?

















What's the form of a valid production or rewriting rule?


	Head or Left-Hand-Side
		(Always a Nonterminal)

	->

	Body or Right-Hand-Side
		(0 or more Terminals and Nonterminals)