Egel is a small toy language based on untyped eager combinator rewriting. Or, equivalently, it is an untyped lambda calculus with constants and strict semantics.
It roughly falls into the same category of combinator languages like Q/Pure and conceptually predates languages like Miranda, ML or Haskell.
The language is homoiconic and supports symbolic rewriting, exceptions, namespaces, and concurrency.
Semantically, the implementation is morally equivalent to an eager term rewriter on a directed acyclic graph with a small twist for performance.
To get a taste of the language an example is shown below.
namespace Fibonacci ( using System def fib = [ 0 -> 1 | 1 -> 1 | N -> fib (N - 2) + fib (N - 1) ] ) using Fibonacci def main = fib 5
The interpreter is implemented in C++. Sources can be downloaded from Github.