csLox

An implementation of Lox interpreted using C#, following this tutorial.

A live demo is available at my personal site here: https://noahpeterson.me/loxInterpreter

Control Structures

• if-then-else
• while, do-while, for
• break, continue

Data Types

Literal values available are floating point numbers, strings, booleans, and nil. Classes can be defined with methods and variables encapsulated.

Standard Library

clock() Returns the system time in seconds.

Truthyness

Everything that is not 'nil' or a 'false' value is true.

Language Extensions

• Errors and warnings include the line and character where the issue starts.
• Multiline comments
• Comma operator
• do-while loops
• continue, break statements
• The + operator can concatenate strings and numbers
• Lambda functions
• Static class methods
• Getter methods
• Multiple Inheritance
• Warnings issued for unused or uninitialized variables, and unreachable code
• Increment and decrement operators ++, --
• Nullcheck operators ??, ?.

Operator Precedence

Highest to Lowest

Name            Operator        Associativity
Call            a(), a., a?.    Left-to-right
postfix         a++, a--        Left-to-right
prefix          ++a, --a        Right-to-left
unary           !a, -a          Right-to-left
factor          /, *            Left-to-right
term            -, +            Left-to-right
comparison      >, >=, <, <=    Left-to-right
equality        !=, ==          Left-to-right
and             and             Left-to-right
or              or              Left-to-right
isNull          ??              Left-to-right
ternary         a?b:c           Right-to-left
assignment      =               Right-to-left
comma           ,               Left-to-right

Grammar

Statements:

program →  declaration* EOF | expression
declaration →  "class" classDeclaration 
            | "fun" function
            |  "var" variableDeclaration
            | statement
classDeclaration →  identifier  ("<" (identifier) ("," identifier)*)? "{" (("class")? function|getter)* "}"
function →  "fun" identifier "(" identifier (, identifier)* ")" block
getter → identifier block
block → "{" declaration* "}"
variableDeclaration → "var" identifier ("=" expression)? (("," term)?)*
statement → print
            | block
            | if | return
            | doWhile | while | for
            | break | continue
            | expressionStatement
print → "print" expression ";"
if → "if" "(" expression ")" statement ("else" statement)?
return →  "return" expression ";"
doWhile → "do" statement "while" "(" expression ")" ";"
while → "while" "(" expression ")" statement
for → "for" "(" (varDeclaration|expressionStatement)? ";" (expression)? ";" (expression)? ")" statement
break → "break" ";"
continue → "continue" ";"
expressionStatement → expression ";" | expression

Expressions:

expression → assignment
assignment → ternaryExpression ("=" assignment)
ternaryExpression → or ("?" equality ":" equality)?
or → and ("or" and)*
and → equality ("and" ternaryExpression)*
equality → comparison (("!="|"==") comparison)*
comparison → term (">"|">="|"<"|"<=" term)*
term → factor ("-"|"+" factor)*
factor → unary ("/"|"*" unary)*
unary → prefix | ("!"|"-" unary)
prefix → ("--"|"++" primary) 
		| postfix
postfix → call 
		| ("--"|"++" call)
call → primary (finishCall | ".")*
finishCall → "(" (expression ("," expression)*) ")"
primary → "false" | "true" | nil |  literal 
		| "(" expression ")" 
		| super "." identifier ";" 
		| "this" | identifier 
		| lambda 
        | "==" | "!=" | ">=" | "<" | "<=" | "/" | "*" | "-" | "+"   //Error productions
lambda → "fun" "(" (identifier ("," identifier)*)? ")" block

Todo: ☐ ☑ ☒

☑ Scanner

• ☑ Multiline comment support

☑ Tokenizer

☑ Syntax Trees

☑ Parser

• ☑ Comma operator- Evaluate and throw away expressions
• ☑ Ternary operator
• ☑ ++, -- operators

☑ Evaluator

• ☑ Allow concatenation of strings and numbers

☑ Statements

• ☑ Support for both expressions and statements

☑ Control Flow

• ☑ do-while loops
• ☑ break statement
• ☑ continue statement

☑ Functions

• ☑ Lambda functions

☑ Resolving and Binding

• ☑ Warnings for unused and uninitialized variables

☑ Classes

• ☑ Static member functions
• ☑ Getter field methods

☑ Inheritance

• ☑ Multiple Inheritance

☑ Deploy to a website

• ☑ Create a Website frontend
• ☑ Create example programs to show off
• ☑ Deploy to a personal site