Compiler Syntax Analysis

What is a Compiler?

• A compiler is a program translating high-level code (Python, Java, C++) into lower-level code (machine code).
• Compilers bridge the gap between human-readable code and machine-executable instructions.
• Compilers translate the entire program before execution.
• Compilers find syntax and semantic errors and optimizes code execution speed.

Phases of Compilation

• Compilation consists of various phases, each using the previous phase's output and feeding its output to the next phase.

Syntax Analysis

• Syntax analysis checks if source code follows the programming language's syntax rules.
• Syntax analysis creates a parse tree.
• A parse tree represents code arrangement according to the language's syntax.
• Example: In if (x > 10) { let y = x + 1; }, the parse tree shows the condition (x > 10) and statements let y = x + 1.

Lexical Analysis

• Lexical analysis is the first compilation step and breaks source code into tokens.
• Tokens include keywords, identifiers, operators, and literals.
• Tokens are passed to the syntax analyzer to ensure they follow the correct syntax.
• Example: let x = 5 + 10; is broken down into tokens: let, x, =, 5, +, 10, and ;.

Grammars

• Grammars are rules defining a language's valid structure.
• Grammars specify how tokens combine to form valid constructs like statements.
• In syntax analysis, grammars verify that tokens form valid statement.
• If code structure doesn’t follow the grammar, the compiler throws an error.
• Example grammar rule: expression → term { ("+" | "-") term } means an expression contains terms connected by plus or minus operators.

Parse Trees and Parse Logic

• A parse tree is a hierarchical representation of source code.
• The parse tree shows how tokens are grouped per syntax rules.
• Parse logic includes used algorithms to build parse trees from tokens.
• Example: For if (x > 10) { let y = x + 1; }, the parse tree has a root labeled if Statement which branches into the condition (x > 10) and the statements (let y = x + 1).
• The parse tree helps visualize relationships between code components.

The Jack Analyzer

• The Jack Analyzer analyzes Jack programs at lexical and syntactical levels.
• The Jack Analyzer breaks down code into tokens and checks its structure against Jack's grammar.
• If code is valid, the Jack Analyzer prepares it for later compilation stages.
• The Jack Analyzer performs lexical and syntax analysis to ensure the code follows language rules.

Importance of Syntax Analysis

• Syntax Analysis catches missing parentheses or misplaced keywords.
• Syntax Analysis catches structural program errors before later compilation stages.

Compilation of Jack Code

• In the Jack language, the compilation process occurs in two stages.
• First, program code compiles into VM code (intermediate form).
• The VM code is translated into machine code.
• Using VM code separates the compilation for easier debugging, modifications, and optimizations.
• The Jack compiler has two main components: syntax analyzer and code generator.
• The module focuses specifically on the syntax analyzer, including a tokenizer and a parser
• The tokenizer generates tokens, and the parser checks their order if arrangement.
• The syntax analyzer produces an output file in XML format.
• The module covers tokenizing, grammars, parsing, and parse trees.
• Understanding compiler construction improves programming skills.

Lexical Analysis Importance

• Lexical analysis identifies and categorizes code elements for processing.
• Lexical analysis eliminates whitespace, comments, for efficient processing.
• Errors like unrecognized characters are caught during lexical analysis.
• The tokenizer is a crucial component of the compilation process in the Jack programming language.
• The tokenizer breaks source code into fundamental units (tokens).
• The tokenizer ignores whitespace and only focuses on meaningful code parts.
• Tokens definitions vary based on the programming language.
• Tokens in Jack include: keywords, symbols, identifiers, integer constants, and string constants.
• Keywords - class, constructor, function, var, if, else, while, do, return.
• Symbols - {, }, (, ), [, ], ;, ,, =, +, -, *, /.
• String Constants - "Hello".
• The tokenizer outputs a token list in XML format, with tokens in XML tags.
• The tokenizer may be implemented as a class or module.
• The tokenizer transforms characters into meaningful tokens and eliminates irrelevant characters.

Grammars Importance

• Grammars define how to construct valid sentences in a language (English, Jack).
• Grammars are used to define syntax of the Jack language.
• Compilers uses grammar to understand and translate code.
• Grammar violations lead to syntax errors.
• Grammars analyze code structure during compilation or interpretation.
• Jack compiler uses grammar to generate a parse tree.
• A grammar has a set of formal rules that define how tokens can form valid structures.
• Grammar rules include terminal rules (actual tokens) and non-terminal rules (higher-level structures).
• The asterisk (*) indicates zero or more occurrences of an element.

Jack Grammar

• The Jack language's grammar is a simplified.
• Specific notations are used to describe the Jack grammar:
• Quotes indicate literal tokens.
• Green text indicates descriptors specific to Jack grammar.
• Parentheses group tokens.
• A vertical bar (|) signifies a choice between options.
• Symbols like question marks (?) and asterisks (*) indicates an element that appears zero or one time.
• Jack’s lexicon consists of keywords, symbols, integer constants, string constants, and identifiers.
• Jack programs include one or more classes, each managed and compiled separately.
• A class starts with the class keyword, a class name, and curly brackets enclosing content.
• Classes may contain optional fields, static variable declarations, and subroutine declarations
• Jack supports limited primitive data types: int, boolean, and char.
• Negative numbers are represented by applying the minus to non-negative values.
• Class types can be user-defined or provided by the Jack OS.
• Jack allows straightforward type conversions between characters and integers.
• To create applications in Jack: Create a new directory, write class files, and use Jack Compiler to compile the program into VM files.
• Input and output are managed through the Jack OS’s Screen and Keyboard classes.
• The OS also provides utility classes, such as a math library for mathematical operations.

Parse Trees and Parse Logic

• The parse tree records the grammatical structure of inputs.
• The parse tree is a classical computer science data structure that begins with a root and branches into sub-trees.
• The grammatical structure sits on top of the input and show its linguistic morphology.
• The parse tree is an abstract artifact using formats like XML.
• Compilation Engine has methods for non-terminal rules in the grammar.
• Parsing logic involves converting an input into a well-organized tree.

Compilation Engine

• Compilation Engine (parser) transforms through methods corresponding to grammar rules.
• Parsing in Jack is recursive and methods invoked for non-terminal rules until all tokens have been processed.
• The generated parse tree can be represented in diagrams or XML.
• Parse trees easier to show relationships between different inputs (statements, expressions, control structures).
• Jack programming parsing logic follows its specific syntax rules:
• The Jack language has grammar rules for parsing expressions, statements, and program structures.
• Compilation Engine parses the Jack program according to its rules.
• Parsing logic breaks down complex constructs into simpler part which are then parsed recursively:
  • For example: terms and factors in expressions.
• Parsing is essential for understanding meaning of any input.
• Parsing logic is a key step in converting code to a structured form that can be analyzed and executed.

The Jack Analyzer

• The Jack Analyzers goal is to understand source code and output it in a structured format, example: XML code.
• The Jack Analyzer output allows for unit-testing in isolations, without using a code generator.
• The XML code output is a parse tree that demonstrates a parser`s understanding of source code.
• Generating XML code involves handling terminal and non-terminal rules in Jack grammar.
• Terminal rules the parser simply wraps in the correct XML tags and outputs them.
• For non-terminal rules, the parser recursively outputs all that constitutes the rule's body.
• Shallow rules (subset of non-terminal rules) do not generate XML output.

Explore compiler syntax analysis: identifying non-primary functions, understanding the necessity of compilers for high-level languages, and describing syntax analysis. Learn about parse tree significance, error detection, phase activities, construct validation, and direct outputs.