We've already seen 2 possible ways to do it.

Cap

End Color

There are really four parts of our parsing state the left hand side nonterminal, some list of terminals and nonterminals before the dot, some list after, and j.

End 1

End 2

End 1

End 2

Round cap

First End Point

Second End Point

Square cap

And you'll see that it's really the difference between the end points.

So can we shift on any of these rules?

And your typical context free grammar is just a set of rewrite rules with a nonterminal symbol on the left, an arrow, and then some terminals and nonterminals on the right.

It can be 1 non terminal like here.

End Point

Second position

To

I could have started with a here.

unexpected end

What's special about the terminals is they never appear on the left side of a rule.

Final score.

Let's take this point right here.

I'm going to be as generic as I can to handle all the possibilities.

A derivation just means starting from some non terminal, follow the rules to derive a sequence of terminals.

A could be empty. B could be empty. Pqr could be empty.

Unexpected end of input

That's going to be true or false.

What I've done here is what's called a derivation.

So let's say we haven't seen any of the input yet.

At the end of Breckenridge Road.

Last stop.

Santiago de Compostela for me, Tom.

It's going to turn out that we'll be able to compute this, fairly systematically, just by remembering the rule for how to compute the closure.

The end of the list of matches has been reached

In a plot behind my old place over on Breckenridge.

I'm going to pick the first one. We'll replace noun with the terminal I.

This is the end of your trip.

First class all the way.

We're just going to return the terminal because that's an example where if you start from a terminal you get a terminal.

Sentence can be replaced with subject followed by verb followed by object.

(a, bb, c).

Here I've recopied the grammar.

Soon as they open that door, it's all over.