both lexical analysis (scanning) and syntax analysis (parsing) involve the use of algorithms and functions to process and analyze the source code. Here's a brief overview of the algorithms and functions used in each of these phases:
1. Lexical Analysis (Scanning):
Regular Expressions: Lexical analyzers often use regular expressions to define the patterns for recognizing tokens in the source code. Regular expressions are used to match keywords, identifiers, literals, and other language constructs.
Finite Automata: Regular expressions are typically compiled into finite automata, which are efficient state machines for recognizing patterns in the input text. Deterministic Finite Automata (DFA) and Non-Deterministic Finite Automata (NFA) are commonly used in this context.
State Transition Functions: These functions define the transitions between states in the lexical analyzer's finite automaton. The transition functions determine how the lexer processes characters from the input stream and moves between states.
2. Syntax Analysis (Parsing):
Context-Free Grammars (CFGs): Parsing is based on context-free grammars, which define the syntax and structure of the programming language. CFGs consist of rules that describe how language constructs can be formed.
Top-Down Parsing Algorithms: Algorithms like recursive descent parsing and LL parsing are used to build the parse tree or AST from the input stream of tokens. These algorithms recursively descend through the grammar rules to make parsing decisions.
Bottom-Up Parsing Algorithms: Algorithms like LR parsing and LALR parsing work from the input tokens up towards the root of the parse tree or AST. These algorithms use a parsing table to guide their decisions.
Shift-Reduce and Reduce-Reduce Actions: In bottom-up parsing, the parser applies shift-reduce and reduce-reduce actions based on the current state and lookahead token. These actions determine how the parse tree or AST is constructed.
Error Recovery Functions: Syntax analyzers often include error recovery mechanisms to handle syntax errors gracefully. These functions can identify and recover from errors in the input code to continue parsing as much of the code as possible.
Both lexical and syntax analysis are essential parts of the compiler's front end. Lexical analysis prepares the source code by breaking it into tokens, while syntax analysis ensures that the code follows the language's grammar and creates a structured representation of the code, such as a parse tree or AST. The algorithms and functions used in these phases play a critical role in understanding and processing the source code correctly.