Parse Tree in Compiler Design

In compiler design, the Parse Tree depicts the syntactic structure of a string in accordance with a given grammar. It was created during the parsing phase of compilation, wherein syntax of the input source code is analyzed. A parse tree is a useful way of showing how a string or program would be derived from a grammar. It does this by breaking down components of that string into smaller units, showing the detail about the grammatical structure that was employed in its creation to obtain an input string. This is a crucial step in syntax validation to allow other steps such as semantic analysis and code generation to proceed with success.

What is a Parse Tree?

A parse tree, also called a syntax tree, is a tree-like hierarchical representation of the derivation of a string according to a formal grammar.

The parse tree is designed in such a way that an in-order traversal-a traversal from left, root, right-produces the original input string. Parse trees represent a fundamental basis for explaining the syntactic structure to source code and assist in error detection and further stages of compilation.

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.

Rules to Draw a Parse Tree

• All leaf nodes need to be terminals.
• All interior nodes need to be non-terminals.
• 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.

Conclusion

Parse trees are one of the most fundamental tools in compiler design. They are used in visualizing and analyzing the syntactic structure of source codes to ensure that they are set correctly according to the rules of the programming language. By these means, it aids in many other stages of compilation, such as the detection of errors and code and its optimization generation. Hence, the parse trees are vital in making a compiler efficient, and understanding them will go a long way in enhancing the design of a programming language.