You might think, Boy, is there a context expensive grammar out there? What's the opposite of free?

But if right above it I've written X 0, then we'd get a different answer.

These grammars that we've been introducing describe something new context free languages.

The set of languages that can be described by re write rules or grammers like this are called context free languages.

I am just gonna pause for a moment to let you think about that.

We'll talk about it in a lot of different contexts.

In theory, you could compose it over here as well.

That line above it is the context.

Finite State Machines, adding a lexer that follows them automatically,

It handles LL. It handles LR. It handles LALR.

like HTML or SQL, the language of database queries.

But that's an example of an application that also uses this sort of linguistic analysis perhaps a little less related to context free grammars but still in the same vein.

It relates grammars to parsing, which is one of the concepts in this class.

So in lecture, we spent a lot of time learning about context free grammars and languages.

Actually, they're both just concise notations for specifying possibly infinite sets of strings.

Sometimes this statement is true, and sometimes it's not.

It depends on the context.

This branch of the family is all about representation.

Here I've written down four claims.

These are both infinite, infinite grammars.

In most interpreters, this is a problem.

All right. Now that you've gone to the hard work of defining all of those procedures,

That's much more important than knowing the particular syntax for any language.

Build the system so that anybody can contribute at any amount.

A context free language is also a set of strings but can be represented by context free grammar, and what these 3 questions are asking us in this problem is to determine the relationship between a regular language and a context free language, so let's say this bubble represents the set of regular languages.

... the misspelled word shown in context...

The brain is recording all information and driving all change in temporal context.

That's an excellent question.

In particular, it's a set of strings that can be represented by a finite state machine or a regular expression.

Well, because, sentences are more interesting.

A context free grammar can capture the language a N and b N, where N is the same.

Another common story or storyline is the claim that we have to get tough .

Y has the value of 2.

This is always true because we have our Pac Man diagram here, and also because you can take any regular language and represent it with a context free grammar.

All right. So, it's another one of these puzzle like questions.

They're the actual input that we're trying to match.

In this problem we've been asked to define a function, cfgempty, which takes in a representation of a context free grammar, a starting state, and a list of visited states and determines whether or not that context free grammar is empty.

The input doesn't really have to be meaningful.

Perhaps a stealth thing.

This is called being lazy, and it's a phenomenal virtue when you're writing programs.

I could just write artery and vein and essentially they would be behaving this way.

Units 3 and 4 were relatively abstract to some degree, intentionally so.

We need to know where we came from in order to know where we're going.

Here's a new quiz. The Great Grammar Fix Up.

And that gives us the entire expression is 0.229.