nikomatsakis

*~

nikomatsakis

Categories

Goals

This proposal is a bridge Haskell's type classes and class-based OOP. It also addresses a pet theme of mine, which is the ability to add methods to classes and define groups of related methods together.

The core unit of organization is called a category, and it is a bundle of statically dispatched methods based on a shared receiver type (a

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The primary goal of this proposal is to eliminate implicit copies of aggregate types, while preserving most other aspects of the language. Secondary goals include: permit references into arrays; make DPS a guaranteed optimization that is obvious from language syntax.

Summary

The following changes are made:

• vectors become fixed-length arrays;

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The "Hashtable Problem"

There is a danger with typeclasses only on functions because they permit a lack of coherence. This danger is particularly acute with collections, where the definition of a particular interface---such as hashable or ord---may be used in structuring the data structure. This renders the data structure corrupt when used with a different implementation.

To see the problem, consider a hashtable defined something like this:

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#!/usr/sbin/dtrace -s

pid$target::upcall_malloc:entry
{
	@task[ustack(10)] = count()
}

pid$target::upcall_shared_malloc:entry
{
	@task[ustack(10)] = count()

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fn foo() -> {x: int, y: int} {
    let x_coord = ...;
    let y_coord = ...;
    ret {y: y_coord, x: x_coord};
}

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;;; etags-select.el --- Select from multiple tags
;;; From http://www.emacswiki.org/emacs/download/etags-select.el

;; Copyright (C) 2007  Scott Frazer

;; Author: Scott Frazer <frazer.scott@gmail.com>
;; Maintainer: Scott Frazer <frazer.scott@gmail.com>
;; Created: 07 Jun 2007
;; Version: 1.13
;; Keywords: etags tags tag select

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enum deser = uint;

iface reader {
    fn read_vec_elt<T:copy>(f: fn() -> T) -> T;
}

impl of reader for deser {
    fn read_vec_elt<T:copy>(f: fn() -> T) -> T {
        f()
    }

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namespace revisions {

using namespace std;

class graph_t;

class version_t {
private:
    graph_t *graph;
    unsigned id;

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Running this program:

use std;
import std::io;

fn iter(&&v: [uint], f: fn(uint)) {
    for i in v { f(i) }
}