The main difference between lexical analysis and syntax analysis is that lexical analysis reads the source code one character at a time and converts it into meaningful lexemes (tokens) whereas syntax analysis takes those tokens and produce a parse tree as an output.
A computer program is a set of instructions that directs the computer to perform the tasks designed in the program. Generally, a programmer writes the program using a high-level language. The computer does not understand these instructions. Therefore, the source code has to convert into machine code to make it understandable by the computer. Moreover, a compiler is a software program that helps to covert the source code into equivalent machine code. It goes through several steps or stages to complete this conversion process. In other words, each phase takes input from the previous stage, and the output goes to the next phase. Overall, lexical analysis and syntax analysis are two steps involved in this compilation process.
Key Areas Covered
1. What is Lexical Analysis
-Definition, Functionality
2. What is Syntax Analysis
-Definition, Functionality
3. Difference Between Lexical Analysis and Syntax Analysis
-Comparison of key differences
Key Terms
Compiler, Lexical Analysis, Syntax Analysis
What is Lexical Analysis
The lexical phase is the first phase in the compilation process. It takes the source code as the input. Furthermore, it scans the source program and converts one character at a time to meaningful lexemes or tokens. The output of lexical analysis goes to the syntax analysis phase. Generally, a lexical analyzer performs lexical analysis.
The format of the token is as follows.
<token-name, attribute-value>
What is Syntax Analysis
The second phase of the compilation process is syntax analysis. It takes the tokens produced by lexical analysis as input and generates a parse tree. The parse tree is also called a syntax tree.
In this phase, the token organizations are checked against the source code grammar. Furthermore, the parser performs syntax analysis. It checks whether the expression made by the tokens is syntactically correct.
In addition to the above two steps, the compilation process also involves phases such as semantic analysis, intermediate code generation, code generation, code optimization etc.
Difference Between Lexical Analysis and Syntax Analysis
Definition
Lexical analysis is the process of converting a sequence of characters into a sequence of tokens while syntax analysis is the process of analyzing a string of symbols either in natural language, computer languages or data structures conforming to the rules of a formal grammar.
Synonyms
Moreover, lexing and tokenization are other names for lexical analysis, whereas syntactic analysis and parsing are the other names for syntax analysis.
Functionality
Lexical analysis reads the source program one character at a time and converts it into meaningful lexemes (tokens) whereas syntax analysis takes the tokens as input and generates a parse tree as output. Thus, this is the main difference between lexical analysis and syntax analysis.
Order
Also, another difference between lexical analysis and syntax analysis is that lexical analysis is the first phase of the compilation process, while syntax analysis is the second phase of the compilation process.
Conclusion
In brief, a compiler is a software program that converts the source code into equivalent machine code. Moreover, it goes through several phases to accomplish this task. Two of them are lexical analysis and syntax analysis. Overall, syntax analysis occurs after lexical analysis. The main difference between lexical analysis and syntax analysis is that lexical analysis reads the source code one character at a time and converts it into meaningful lexemes (tokens) whereas syntax analysis takes those tokens and produce a parse tree as an output.
References:
1.“Compiler Phases – Javatpoint.” Www.javatpoint.com, Available here.
2.“Lexical Analysis.” Wikipedia, Wikimedia Foundation, 8 July 2019, Available here.
3.“Parsing.” Wikipedia, Wikimedia Foundation, 15 May 2019, Available here.
Image Courtesy:
1.”An ideal multi-language, multi-target compiler” By I, Surachit (CC BY-SA 3.0) via Commons Wikimedia
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