A context free grammar is a grammar which satisfies certain properties. In computer science, grammars describe languages; specifically, they describe formal languages. A formal language is just a set (mathematical term for a collection of objects) of strings (sequences of symbols… very similar to the programming usage of the word “string”). A simple example of … Read more
How to write regular expression for a DFA In any automata, the purpose of state is like memory element. A state stores some information in automate like ON-OFF fan switch. A Deterministic-Finite-Automata(DFA) called finite automata because finite amount of memory present in the form of states. For any Regular Language(RL) a DFA is always possible. … Read more
Regular grammar is either right or left linear, whereas context free grammar is basically any combination of terminals and non-terminals. Hence you can see that regular grammar is a subset of context-free grammar. So for a palindrome for instance, is of the form, S->ABA A->something B->something You can clearly see that palindromes cannot be expressed … Read more
How to write CFG with example ambn L = {am bn | m >= n}. Language description: am bn consist of a followed by b where number of a are equal or more then number of b. some example strings: {^, a, aa, aab, aabb, aaaab, ab……} So there is always one a for one … Read more
Below is my (current) favorite demonstration of why parsing C++ is (probably) Turing-complete, since it shows a program which is syntactically correct if and only if a given integer is prime. So I assert that C++ is neither context-free nor context-sensitive. If you allow arbitrary symbol sequences on both sides of any production, you produce … Read more
Pattern Recursion With recursive patterns, you have a form of recursive descent matching. This is fine for a variety of problems, but once you want to actually do recursive descent parsing, you need to insert capture groups here and there, and it is awkward to recover the full parse structure in this way. Damian Conway’s … Read more