Lox Interpreter written in C++

my exercise for codecrafters' online judge repo see here; this is a more detailed version of my exercise's codebase.

from Crafting Interpreters

Build

A C++23 compiler is required to build the project; tested with gcc, clang, and MSVC. Bazel or CMake is required to build the project.

Debug mode

with Bazel(currently only configured for Windows)

bazel build //tools:intepreter # build the interpreter
bazel test //tests:... # run the tests

with CMake

vcpkg is required to install the dependencies. Make sure the option AC_CPP_DEBUG is set to ON in the CMakeLists.txt file.

cmake --preset= # see available presets, make sure to alter the toolchain file

Release mode

No external dependencies are required for release mode. You can run Bazel or CMake as mentioned above(only for target interpreter), or run the run.sh script in the root directory(Linux) .

Run

Run the interpreter

by default the interpreter will output nothing in debug mode but only spdlog messages. comment the code in execution_context.hpp, line 148-151 to see the output.

interpreter tokenize <source>
interpreter parse <source>
interpreter evaluate <source>
interpreter run <source>
# repl was on the way... but not in a forseeable future...

Grammar

Syntax

program        → declaration* EOF ;

Declaration

declaration    -> varDecl
                | statement
                | funcDecl ;

varDecl        -> "var" IDENTIFIER ( "=" expression )? ";" ;
funcDecl   -> "fun" function ;  

Statement

statement      -> exprStmt
                | printStmt
                | block
                | ifStmt
                | whileStmt
                | forStmt
                | returnStmt ;

exprStmt        -> expression ";" ;
printStmt       -> "print" expression ";" ;
block           -> "{" declaration* "}" ;
ifStmt          -> "if" "(" expression ")" statement ( "else" statement )? ;
whileStmt       -> "while" "(" expression ")" statement ;
forStmt         -> "for" "(" ( varDecl | exprStmt | ";" )
                           expression? ";"
                           expression? ")" statement ;
returnStmt      -> "return" expression? ";" ;

Expression

expression     -> assignment ;

assignment     -> IDENTIFIER "=" assignment
                | logic_or ;

logic_or       -> logic_and ( "or" logic_and )* ;
logic_and      -> equality ( "and" equality )* ; 
equality       -> comparison ( ( "!=" | "==" ) comparison )* ;
comparison     -> term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
term           -> factor ( ( "-" | "+" ) factor )* ;
factor         -> unary ( ( "/" | "*" ) unary )* ;
unary          -> ( "!" | "-" ) unary
                | call ;
call           -> primary ( "(" arguments? ")" )* ;

primary        -> NUMBER | STRING | "true" | "false" | "nil"
                | "(" expression ")" | IDENTIFIER ;

Miscellaneous

arguments     -> expression ( "," expression )* ;
function      -> IDENTIFIER "(" parameters? ")" block ;
parameters    -> IDENTIFIER ( "," IDENTIFIER )* ;
alnums        -> [a-zA-Z0-9] 
               | [.!@#$%^&*()] 
               | [...] ;

Lexical

number        -> digit + ( "." digit + )? ;
string        -> "\"" + ([[alnums]])* + "\"" ;
identifier    -> [a-zA-Z_] + [a-zA-Z0-9_]* ;

note: the cpp was just for syntax highlighting in vscode to make it look prettier than plain text.

Project Structure

generated by Bazel

Notes

This exercise is still in active development, and I will be updating it as I progress through the book.

TODO(pirority from high to low)

• Binding and resolving
• Add class support
• JVM bytecode generation
• Add class inheritance support
• LLVM IR generation
• (may never realize 😂)Machine code generation(x86_64, risc-v)