Syntax Analyzer vs Lexical Analyzer

Lexical Analyzer vs Syntax Analyzer

• Lexical analyzer deals with simple non-recursive constructs of a language.
• Syntax analyzer deals with recursive constructs of a language.
• Lexical analyzer recognizes the smallest meaningful units (tokens) in a source program.
• Syntax analyzer works on the smallest meaningful units (tokens) in a source program to recognize meaningful structures.

Parsing Techniques

• Parsing techniques are categorized into two groups: Top-Down Parsing and Bottom-Up Parsing.
• Top-Down Parsing: construction of the parse tree starts at the root and proceeds towards the leaves.
• Top-Down Parsing can be further divided into Recursive Predictive Parsing and Non-Recursive Predictive Parsing (LL Parsing).
• Bottom-Up Parsing: construction of the parse tree starts at the leaves and proceeds towards the root.
• Bottom-Up Parsing is also known as shift-reduce parsing and puts information about identifiers into the symbol table.

Lexical Analyzer

• Regular expressions are used to describe tokens (lexical constructs).
• Deterministic Finite State Automaton (DFA) can be used in the implementation of a lexical analyzer.
• Lexical analyzer simplifies the job of the syntax analyzer.

Syntax Analyzer

• A syntax analyzer creates the syntactic structure (generally a parse tree) of the given program.
• A syntax analyzer is also called a parser.
• The syntax of a language is specified by a Context Free Grammar (CFG).
• The rules in a CFG are mostly recursive.
• A syntax analyzer checks whether a given program satisfies the rules implied by a CFG or not.

Semantic Analyzer

• A semantic analyzer checks the source program for semantic errors and collects the type information for the code generation.
• Type-checking is an important part of semantic analyzer.
• Context-free grammars used in the syntax analysis are integrated with attributes (semantic rules) – the result is a syntax-directed translation, – Attribute grammars.

Intermediate Code Generation

• A compiler may produce an explicit intermediate codes representing the source program.
• These intermediate codes are generally machine (architecture independent).
• The level of intermediate codes is close to the level of machine codes.

Code Optimizer

• The code optimizer optimizes the code produced by the intermediate code generator in the terms of time and space.
• Faster code or target code that consumes less power.

Code Generation

• Produces the target language (Machine code) in a specific architecture.
• It depends on the computer architecture: i.e motherboard, cpu,…
• The target program is normally a relocateable object file containing the machine codes.

Other Applications

• Techniques used in compiler design can be applicable to many problems in computer science.
• Techniques used in a lexical analyzer can be used in text editors, information retrieval system, and pattern recognition programs.
• Techniques used in a parser can be used in a query processing system such as SQL.
• Many software having a complex front-end may need techniques used in compiler design.
• A symbolic equation solver which takes an equation as input uses techniques used in compiler design.
• Most of the techniques used in compiler design can be used in Natural Language Processing (NLP) systems.