Explain Chomsky hierarchy with example?

The Chomsky hierarchy is a way of categorizing different types of grammar, or rules for how words and sentences are put together in a language. It was created by a linguist named Noam Chomsky. The hierarchy has four levels, each with its own type of grammar.

1. Type 3: Regular Grammar - This is the simplest type of grammar. It's like following a very basic recipe where you only have one or two steps. An example would be a password that must start with a letter and end with a number. The rule is simple and doesn't change.

2. Type 2: Context-Free Grammar - This is a bit more complex. It's like a recipe where you can add the ingredients in any order you want. An example would be sentences in English. You can often rearrange the words in a sentence and it will still make sense. For example, "The cat chased the mouse" and "The mouse was chased by the cat" both mean the same thing.

3. Type 1: Context-Sensitive Grammar - This is even more complex. It's like a recipe where the order you add the ingredients can change the final result. An example would be languages that change a word based on the words around it. In German, for example, the word for "the" changes based on the gender of the noun it's attached to.

4. Type 0: Unrestricted Grammar - This is the most complex type of grammar. It's like cooking without a recipe, where you can do anything you want. An example would be human languages in general. There are so many rules and exceptions to those rules that it's like there are no restrictions at all.

So, the Chomsky hierarchy is like a ladder of complexity for language rules, starting from the simplest at the bottom (Type 3) and going to the most complex at the top (Type 0).