billhails/F-Natural

Small Functional Lambda Language with first class environments

A deliberately small, purely functional language with ML-like semantics and javascript-like syntax.

I have several partially working prototypes for this language, implemented in various languages, while
trying to iron out the basic behavior.

While I'd like to write this in C, I think I need an OO language to do it neatly, so I'm going to try to
work in a functional subset of C++.

// Examples:

fn factorial (n) {
    if (n == 0) { 1 }
    else { n * factorial(n - 1) }
}

// or, more idiomatically using pattern matching:
fn factorial {
    (0) { 1 }
    (n) { n * factorial(n - 1) }
}

// first class environments
env foo {
    fn bar() { "baz" }
}

// { expression evaluating to an environment } '.' { expression evaluated in that environment }
foo.bar(); // "baz"

// create a polymorphic type "List of t" with constructors "Pair" and Null":
typedef List(t) { Pair(t, List(t)) | Null }

// length() is then polymorphic:
fn length {
    (Null) { 0 }
    (Pair(first, rest)) { 1 + length(rest) }
}

// or use F-Natural's built-in list constructor "@" and list syntax "[]"
fn length {
    ([]) { 0 }
    (first @ rest) { 1 + length(rest) }
}

// strings are lists of chars:
'b' @ [ 'a', 'z' ]; // "baz"

// "@@" is list append:
['b'] @@ "az"; // "baz"