Functional programming language for Python programmers and friends

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

<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    #<em> lower bound</em>
        <strong>Int</strong> upper = 300  #<em> upper bound</em>
        <strong>Int</strong> step = 20    #<em> step</em>
        <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:

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

_ _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.