Parse Tree in Compiler Design

Here we will study the concept and uses of Parse Tree in Compiler Design. First, let us check out two terms :

• Parse : It means to resolve (a sentence) into its component parts and describe their syntactic roles or simply it is an act of parsing a string or a text.
• Tree: A tree may be a widely used abstract data type that simulates a hierarchical tree structure, with a root value and sub-trees of youngsters with a parent node, represented as a group of linked nodes.

Parse Tree:

• Parse tree is the hierarchical representation of terminals or non-terminals.
• These symbols (terminals or non-terminals) represent the derivation of the grammar to yield input strings.
• In parsing, the string springs using the beginning symbol.
• The starting symbol of the grammar must be used as the root of the Parse Tree.
• Leaves of parse tree represent terminals.
• Each interior node represents productions of a grammar.

Rules to Draw a Parse Tree:

1. All leaf nodes need to be terminals.
2. All interior nodes need to be non-terminals.
3. In-order traversal gives the original input string.

Example 1: Let us take an example of Grammar (Production Rules).

S -> sAB
A -> a
B -> b

The input string is “sab”, then the Parse Tree is:

Example-2: Let us take another example of Grammar (Production Rules).

S -> AB
A -> c/aA
B -> d/bB

The input string is “acbd”, then the Parse Tree is as follows: 

Uses of Parse Tree:

• It helps in making syntax analysis by reflecting the syntax of the input language.
• It uses an in-memory representation of the input with a structure that conforms to the grammar.
• The advantages of using parse trees rather than semantic actions: you’ll make multiple passes over the info without having to re-parse the input.

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