Cmel

Cmel (see-mel) is short for Caramel, the name of my cat. It's my implementation of Lox from Crafting Interpreters by Robert Nystrom.

Features

Here are the features which separate Cmel from Lox.

• Support for 2^24 constant values in a script
• Local const values
• Has a break statement to exit from loops early
• Built-ins
• Primitive methods (e.g. "string".length())
• Lists
• Maps (hash tables with string keys)
• Modulo operator
• String escape sequences (\n, \t, \r, \", \\, \e)
• Automatic type-to-string conversion with the + operator
• Module system with import statement and standard library

Primitive Types

• Nil
• Boolean
• String
  • length() returns the number of characters in the string
  • split(delimiter) returns a list of elements in the given string as separated by the delimiter
  • Supports escape sequences: \n (newline), \t (tab), \r (carriage return), \" (quote), \\ (backslash)
  • When using the + operator with a string and any other type, the non-string operand is automatically converted to a string (e.g., "Answer: " + 42 produces "Answer: 42")
• Number
  • add(Number) returns the number plus the passed number
• List
  • add(value) mutates the list by adding the given value and returns the same list
  • remove(index) mutates the list by removing the value at the given index and returns the same list
  • length() returns the length of the list
• Map (hash table with string keys)
  • keys() returns a list of all keys in the map
  • values() returns a list of all values in the map
  • has(key) returns true if the key exists in the map
  • remove(key) removes the key-value pair and returns the value (or nil if not found)
  • length() returns the number of key-value pairs in the map
  • Access via subscript: map["key"] returns value or nil
  • Set via subscript: map["key"] = value
  • Literal syntax: {"key1": value1, "key2": value2}

Module System

Import functions from .cmel modules using the import statement:

import PI, sqrt, abs from "stdlib/math";
print PI;        // 3.14159
print sqrt(16);  // 4
print abs(-5);   // 5

// Wildcard import
import "stdlib/io";
var time = clock();

All native functions require imports. Modules are executed once and cached.

Standard Library:

• stdlib/convert.cmel - Type conversion utilities: number()
• stdlib/io.cmel - I/O functions: clock(), input(), readFile()
• stdlib/math.cmel - Native math functions: abs(), max(), min(), pow(), sqrt(), and constants PI, E
• stdlib/string.cmel - String functions: startsWith(), endsWith(), join(), reverse()
• stdlib/list.cmel - List functions: slice(), sort(), sortWith(), createListWithDefaults()
• stdlib/test.cmel - Testing framework: suite(), test(), assert(), assertEqual(), run()

Installation

Quick Install

To build and install Cmel system-wide:

./install.sh

This will compile the interpreter and install it to /usr/local/bin, making it available from anywhere on your system.

After installation, you can run:

cmel              # Start REPL
cmel <file.cmel>  # Run a Cmel file

Uninstall

To remove Cmel from your system:

./uninstall.sh

Usage

Manual Build (without installing)

Compile the project using:

./build.sh

Then, you can either run cmel as a REPL:

./cmel

or execute a file by passing it the path:

./cmel <filepath>

Testing

To test the code, first build the executable using the build script, then run

node cmel.test.mjs

Tests use inline expectations with // expect: comments.

Todo

Language Features

• Widen const to work for global variables
• Arrays/Lists
• File Reading
• Postfix Operators (e.g. ++ and --)
• Ternary Operator
• Modulo Operator
• String Escape Characters
• String interpolation
• Implicit convert to string on all types for concatenation
• Try/Catch
• Anonymous Functions
• Modules
• User facing Hash Tables (string keys only)
• Hash Tables
• Hash Tables with non-string keys
• Continue Statement
• Break Statement
• Switch Statement
• Typeof operator
• toString method on instances

Tooling

• Syntax Highlighter
• Language Server
• Test Runner

Misc

• In chapter 18 it's mentioned that a <= b should not be the same as !(a > b) but in cmel it is. Fix by introducing dedicated instructions for <=, >= and maybe != while you're at it