Blog of Julian Andres Klode

Debian, Ubuntu, Linux in general, and other free software

Posts Tagged ‘pure

Functional programming language for Python programmers and friends

Just for you, and this time in the Pythonesque rendering.

module main:
    import std (range)
    import std.io (printf, IO)

    # print the Fahrenheit-Celcius table for fahr = 0, 20, ..., 300
    function main(mutable IO io):
        Int lower = 0    # lower bound
        Int upper = 300  # upper bound
        Int step = 20    # step
        for Int fahr in range(lower, upper, step):
            Double 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

module std.container.list:

    ## The standard singly-linked list type
    type List[E]:
        Nil                     ## empty list
        Node:
            E value             ## current value
            List[E] next        ## remaining list
 


And yes, both languages should be able to be represented using the same abstract syntax tree. The only change is the replacement of the opening curly brace by a colon, the removal of the closing curly bracket and semicolons, the replacement of C-style comments with Python-style comments and the requirement of indentation; oh and the for statement gets a bit lighter as well.

Written by Julian Andres Klode

April 1, 2012 at 18:33

[updated] Functional programming language for C programmers and friends

Just for you:

module main {
    import std (range);
    import std.io (printf, IO);
 
    /* print the Fahrenheit-Celcius table
        for fahr = 0, 20, ..., 300 */
    function main(mutable IO io) {
        Int lower = 0;   // lower bound
        Int upper = 300; // upper bound
        Int step = 20;   // step
        for (Int fahr in range(lower, upper, step)) {
            Double 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

module std.container.list {

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

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.

Written by Julian Andres Klode

April 1, 2012 at 17:41

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