meyer1994 / grammar Goto Github PK

The user must be able to:

• Edit CFGs (via text)

• Show the intermediary grammars for the proper grammar conversion (without useless symbols etc.)

First and FirstNT methods.

FirstNT is the same as First, but with the terminal symbols filtered out.

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A proper CFG has the following properties:

• No unreachable symbols

• No unproductive symbols

• No epslon productions

• No cyles

To get a proper grammar we must implement the following methods:

• Remove unproductive symbols

• Remove unreachable

• Remove epslon productions

• Remove cycles (simple productions)

We need to apply the above methods in the following order:

1. Remove epslon productions

2. Remove useless symbols

   1. Remove unproductive
   2. Remove unreachable

3. Remove simple productions

• Check if there is left recursion

• Identify left recursion (direct or indirect)

• Identify non-terminals that have left recursion

• Eliminate left recursions

• Check if the the CGF is factored

• Check if it can be factored in n steps

Make functions to check the followin properties.

• Infinite

• Empty

• Finite