Projects / Rhea


Rhea is a simple, type safe, partially type inferred, garbage collected programming language which compiles to C.

Rhea’s grammar is defined in ANTLR v4 EBNF, and the compiler is implemented in C#.


fun fib(n : int64) -> int64 {
  if (n == 0) {
    return 0
  if (n == 1) {
    return 1
  return fib(n - 2) + fib(n - 1)

fun main() -> int64 {
  return fib(10)



Line comments start with # and end at the end of the line:

# This is a comment.

Reserved Words

extern, false, for, fun, if, return, struct, true, and var


Identifiers begin with a letter and may contain letters, numbers, and underscores.


Rhea uses curly braces to define blocks. You can use a block anywhere a statement is allowed, like in control flow statements. Function bodies are also blocks.

Precedence and Associativity

Precidence Operator Description Associates
1 () Grouping Left
2 - Negate Right
3 * / % Multiply, Divide, Modulo Left
4 + - Add, Subtract Left
5 < <= > >= Comparison Left
6 == != Equal, Not Equal Left



A boolean value represents truth or falsehood. There are two boolean literals, true and false.


Rhea has eight integer types. Four signed: int8, int16, int32, and int64, and four unsigned: uint8, uint16, uint32, and uint64.

There are two floating point types: float32, and float64.


Strings have a type of string and are always allocated on the heap.

Strings are technically structs. The Rhea standard library provides a number of methods to make working with strings easier.

string#dup() -> string

Duplicates a string.

var duplicate = "Hello World".dup()

string#trim() -> string

Trims leading and trailing whitespace from a string.

var trimmed = "  Hello World  ".trim()

string#length() -> int64

Returns the length of a string.

var length = "Hello World".length()


Function are declared using the fun keyword:

fun foo(bar : int32) -> int64 {
  # ...

This creates a new function which accepts a 32-bit integer as an argument and returns a 64-bit integer.

There is no need to declare functions before calling them.


Variables are declared using the var keyword:

var name : string

This creates a new string, name, in the current scope.

Variables can also be initialized when they’re created. In this case, their type can be inferred:

var name = "Glarpy"

Control Flow

If Statements

if (x == 0) {
  # ...

For Statements


for (var x in 0..10) {
  # ...



struct point {
  x : int64
  y : int64

Member Access

var origin : point
point.x = 1


Methods are special functions which take a struct as an argument.

fun string#newTrim(self : string) -> string {
  return self.trim()

fun main() -> int64 {
  return " foo ".newTrim().length()

Calling C from Rhea

Use the extern keyword.

extern fun some_c_function() -> int32

fun main() -> int32 {
  return some_c_function()