## What is followpos?

• followpos(i): the set of positions that can follow. position i in any generated string.

## What is the rule to compute Firstpos if the node is?

6.2.3 firstpos() The function firstpos(n) is defined as the set of positions that can match the first symbol of a string generated by the sub-tree at node “n”. It is defined for all the nodes and depends on the firstpos() values of the leaf nodes.

**What is nullable in syntax tree?**

Then formal description of three important operators checking null-ability and computing first and last positions of all the internal nodes of the syntax tree are described. Nullable is a Boolean function having value true or false and its value depends upon the type of node.

**How DFA based pattern matcher can be optimized?**

In this section we present three algorithms that have been used to implement and optimize pattern matchers constructed from regular expressions. The third algorithm produces more compact representations of transition tables than the standard, two-dimensional table. …

### How do you find first and follow in compiler?

For any production rule A → αBβ,

- If ∈ ∉ First(β), then Follow(B) = First(β)
- If ∈ ∈ First(β), then Follow(B) = { First(β) – ∈ } ∪ Follow(A)

### What is the length of the shortest string not in the language over alphabet 0 1?

Check each string generated over the alphabet {0, 1} until you reach the shortest string which is not generated by the given regular expression. In this case, smallest string which is not generated by the given regular expression is 0110, whose length is four.

**What Is syntax tree in compiler design?**

An abstract syntax tree (AST) is a way of representing the syntax of a programming language as a hierarchical tree-like structure. This structure is used for generating symbol tables for compilers and later code generation. The tree represents all of the constructs in the language and their subsequent rules.

**What does a syntactic analyzer do?**

What does a Syntactic Analyser do? Explanation: Syntax analyzer will just create a parse tree. Semantic Analyzer checks the meaning of the string parsed.

#### Can we convert regex to DFA?

This method is given below: Step 1: Design a transition diagram for given regular expression, using NFA with ε moves. Step 2: Convert this NFA with ε to NFA without ε. Step 3: Convert the obtained NFA to equivalent DFA.