Abstract Syntax Tree vs Parse Tree

Abstract Syntax Trees (ASTs) and Parse Trees (PTs) are two fundamental concepts in computer science and software engineering. Understanding the differences between them is essential for writing efficient and robust code. This blog post will look at both ASTs and PTs and compare their main features.

What is an Abstract Syntax Tree?

An Abstract Syntax Tree, or AST, is a representation of the structure of a programming language. It is a tree-like structure that is composed of nodes, each of which represents a language element like a variable, operator, or keyword. ASTs are often used to represent code written in a specific programming language, such as Python or C++. 

• An AST is essentially a simplified version of a parse tree. 
• The nodes of an AST are abstracted away from the details of the syntax of the language, making it easier to reason about the structure of the code. 
• This abstraction allows for more efficient processing, as the details of the language are removed. Additionally, ASTs are often easier to understand than parse trees, as they are more concise and easier to read.

What is a Parse Tree?

A Parse Tree, or PT, is a tree-like structure that represents the syntactic structure of a programming language. It is composed of nodes, each of which corresponds to a language element such as a variable, operator, or keyword. Unlike ASTs, PTs are not abstracted away from the details of the language syntax. This means that a PT is a more detailed representation of the code, which can be useful for debugging.

Abstract Syntax Tree vs Parse Tree:

Factor	Abstract Syntax Tree	Parse Tree
Structure	An AST is composed of symbols, such as operators, identifiers, and keywords. These symbols are organized in a tree structure.	A parse tree is composed of tokens, such as terminal and non-terminal symbols. These tokens are organized in a tree structure.
Representation	An AST is represented using a standard tree structure, with each node representing a particular symbol or rule.	A parse tree is represented using a graph structure, with each node representing a particular token or rule.
Generation	An AST is generated by the compiler from the source code.	A parse tree is generated by the parser from the source code.
Usage	An AST is used to analyze the source code and optimize it for compilation.	A parse tree is used to check the syntactic correctness of the source code.
Expressiveness	An AST is more expressive than a parse tree, as it provides more information about the source code.	A parse tree is less expressive than an AST, as it only provides basic information about the source code.
Efficiency	An AST is more efficient than a parse tree, as it requires fewer operations to generate.	A parse tree is less efficient than an AST, as it requires more operations to generate.
Size	An AST is smaller than a parse tree, as it contains fewer symbols.	A parse tree is larger than an AST, as it contains more tokens.
Complexity	An AST is simpler than a parse tree, as it is generated from fewer operations.	A parse tree is more complex than an AST, as it is generated from more operations.
Comprehension	An AST is easier to comprehend than a parse tree, as it contains more information about the source code.	A parse tree is harder to comprehend than an AST, as it contains less information about the source code.