End Color

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.

unexpected end

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

Shields at 32 .

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.

Shields up!

Starting up the shield.

Shields up.

We're losing our shields.

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.

Shield amount

They have shield generators!

Activate ray shields.

Ray shields.

Raise the shield.

Their shield is down.

Deflector shields are holding.

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.

And we keep on doing that, slice after slice.

Let's say that we've got x goes to ab dot cd coming from position j in chart i.

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

The replacement can be anything.

Let's activate the shields for security reasons. Some fragments of the wreck could hit us.

Prepare to open shield.

Shields up.

Aft shields at 50 .

Their shields are down.

Power the shields!

They've breached the shield!

Here is our tree, and at various places although it's starting with the trunk or the root it branches out, and all of these intermediate parts in the tree represent none terminals in the grammar.