jlox

Lox

 // Your first Lox program!
 print "Hello, world!";

• Dynamic typing
• Automatic memory management
• Data Types
  • Booleans
  • Numbers
  • Strings
  • Nil
• Expressions
  • Arithmetic
  • Comparison and equality
  • Logical operators
  • Precedence and grouping
• Statements
• Variables
• Control Flow
• Functions
• Closures
• Classes

A Grammar for Lox expressions

• Literals. Numbers,strings,Booleans, and nil

• Unary expressions. A prefix ! to perform a logical not, and - to negate a number.

  • Binary expressions. The infix arithmetic(+,-,*,/) and logic operators (==, !=, <, <=,>,>=)

    • Parentheses. A pair of ( and ) wrapped around and expression.

      • Syntax tree - Expression

        expression     → literal
        | unary
        | binary
        | grouping ;
        
        literal        → NUMBER | STRING | "true" | "false" | "nil" ;
        grouping       → "(" expression ")" ;
        unary          → ( "-" | "!" ) expression ;
        binary         → expression operator expression ;
        operator       → "==" | "!=" | "<" | "<=" | ">" | ">="
        | "+"  | "-"  | "*" | "/" ;
        
        

      | Name | Operators | Associates |

            |------------|-----------|------------|
      

      | Equality | == != | Left | | Comparison | > >= < <= | Left | | Term | - + | Left | | Factor | / * | Left | | Unary | ! - | Right |

        expression     → equality ;
        equality       → comparison ( ( "!=" | "==" ) comparison )* ;
        comparison     → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
        term           → factor ( ( "-" | "+" ) factor )* ;
        factor         → unary ( ( "/" | "*" ) unary )* ;
        unary          → ( "!" | "-" ) unary
                       | primary | call ;
        call           → primary( "(" arguments? ")" )* ;
        arguments       → expression ( "," expression)* ;
        primary        → NUMBER | STRING | "true" | "false" | "nil"
                       | "(" expression ")" | IDENTIFIER ;
      

      • Syntax tree - Statement

        program        → statement* EOF ;
              
        statement      → exprStmt
                       | printStmt 
                       | block;
                    
        block         → "{" declaration* "}"
              
        exprStmt       → expression ";" ;
        printStmt      → "print" expression ";" ;
        

      A program is a list of statements followed by the special "end of file" token. The mandatory end token ensures the parse consumes the entire input and don't silently ignore erroneous unconsumed tokens at the end of a script.

      • Syntax tree - add Variable syntax

        program   → declaration* EOF ;
                  
        declaration  → funDecl
                     | varDecl
                     | statement ;
        
        statement      → exprStmt
                       | forStmt
                       | ifStmt
                       | printStmt
                       | returnStmt
                       | whileStmt
                       | block ;
         funDecl       → "fun" function;
         function      →  IDENTIFIER "(" parameters? ")" block ;
         block         → "{" declaration* "}"
         ifStmt        → "if" "(" expression ")" statement ( "else" statement)? ;
                    
        varDecl  → "var" IDENTIFIER ( "=" expression )? ";" ;
        returnStmt → "return" expression? ";";
        

      • Syntax tree -- Logical Operators

        expression     → assignment ;
        assignment     → IDENTIFIER "=" assignment
        | logic_or ;
        logic_or       → logic_and ( "or" logic_and )* ;
        logic_and      → equality ( "and" equality )* ;
        

      whileStmt → "while" "(" expression ")" statement ; forStmt → "for" " (" (varDecl | exprStmt | ";")

                expression? ";" expression? ")" statement ;