[updated] Functional programming language for C programmers and friends

Just for you:

<strong>module</strong> main {
    <strong>import</strong> std (range);
    <strong>import</strong> std.io (printf, IO);

    <em>/* print the Fahrenheit-Celcius table
        for fahr = 0, 20, ..., 300 */</em>
    <strong>function</strong> main(<strong>mutable</strong> IO io) {
        <strong>Int</strong> lower = 0;   <i>// lower bound</i>
        <strong>Int</strong> upper = 300; <i>// upper bound</i>
        <strong>Int</strong> step = 20;   <i>// step</i>
        <strong>for</strong> (<strong>Int</strong> fahr in range(lower, upper, step)) {
            <strong>Double</strong> celcius = 5 * (fahr - 32) / 9;
            std.io.printf(io, "%3d\t%6.1f\n", fahr, celcius);
        }
    }
}

It does not really look like it, but this language is purely functional. It represents side effects using unique types. If you declare a mutable parameter, you basically declare a unique input parameter and a unique output parameter.

I’m also giving you a list implementation

<strong>module</strong> std.container.list {

    <i>/** The standard singly-linked list type */</i>
    <strong>type</strong> List[E] {
        Nil;                    <i>/** empty list */</i>
        Node {
            E value;            <i>/** current value */</i>
            List[E] next;       <i>/** remaining list */</i>
        }
    }
}

Thus are only excerpts from a document with tens of pages and the reference implementation of the standard library. The incomplete working draft for the language is attached: JAK Programming Language Early Working Draft (28 pages).

Update: Fixed the link.