Fixnum

12 năm trướcdiscuss

On the other hand, the burden of proof is on the library writer who creates the typeclass instance, not on the end user - possible largely thanks to purity - whereas programmers may expect to re-implement various patterns by hand.

Fixnum

12 năm trướcdiscuss

It could be related to StackOverflow displaying "Hot Network Questions" in a sidebar, some of which are from the aviation StackExchange, combined with the usual phenomenon of upvoted stories attracting similar submissions.

Incidentally, I find this sidebar extremely distracting; maybe it's time for a plugin/script to fix it.

Fixnum

12 năm trướcdiscuss

Julia seems nice, but the fact that the developers don't care about TCO is annoying and vaguely reminiscent of Python. If this were added, not only would many algorithms become more natural to express, but it'd go to the top of my list as a recommended first language (instead of Scheme or Lua).

Fixnum

13 năm trướcdiscuss

It's being fixed.

http://www.reddit.com/r/haskell/comments/1rpte3/explanation_...

Fixnum

13 năm trướcdiscuss

They're not similar at all. FoCS is mostly about introductory programming and data structures (with a tiny bit about automata). Sipser's book is about computation and complexity - it's comparable to Hopcroft and Ullman's Intro to automata theory, languages, and computation, for which Ullman recommends FoCS or equivalent as a prerequisite.

Fixnum

13 năm trướcdiscuss

Actually, Scheme is more accessible than ever before. If installing MIT Scheme and Edwin/Emacs is too difficult, now there's Racket-SICP, which allows you to program with DrRacket, a beginner-friendly graphical IDE, and actually comes with implementations of some parts of SICP that MIT Scheme omitted, like the picture language and (afaik) some concurrency primitives.

Is Scheme really decreasing in usage? Sure, in recent years there have been high-profile moves to Python at MIT and UCB, but I don't know of any hard stats on worldwide Scheme usage. Not that it matters.

Fixnum

13 năm trướcdiscuss

For one thing, you generate as few as possible by aggressively fusing away intermediate lists (at least if your language is pure).

Also, the garbage collector will often move lists into contiguous region(s) of memory.

More to the point, though, sometimes a list is the appropriate data structure for a problem (like returning all intermediate results from the Collatz call, where you don't know how many there will be). Sure, you could use an array and double its size every now and then, but you're doing an awful lot of violence to your program just to handle something the runtime could take care of for you :)

And yes, I know there will be a slight performance penalty under many circumstances.

Fixnum

13 năm trướcdiscuss

The point is you're supposed to use truly random word combinations since those are at least memorable.

  $ wc -l /usr/share/dict/words
  119095
  $ python -c 'print(119095 ** 4)'
  201175048646341950625
  $ python -c 'print(85 ** 10)'
  19687440434072265625

So, even if your target is known to be using this scheme in pure form, this has more entropy than a completely random 10-digit password (assuming ~85 characters) -- and who would actually be using such a thing, except someone using a password management program - who could just as easily be using a 20-character random password?

So even if it becomes known, it's an improvement on what users are doing now.

Fixnum

13 năm trướcdiscuss

DARPA is trying it:

http://www.crash-safe.org/node/9

Fixnum

13 năm trướcdiscuss

For imperative languages, the most popular approach to formal proof is to add partial correctness annotations in an axiomatic semantics such as Hoare logic. I've heard that Microsoft does this to verify many properties of the Windows kernel. (I think the most popular tools are 3rd-party and proprietary at the moment.) Of course, finding the right theorems to write down is not easy either.

There's currently an attempt to formalize a subset of C, with an axiomatic semantics, all the way from specification down to machine language: http://vst.cs.princeton.edu/

Fixnum

13 năm trướcdiscuss

I think Vidarh's point is that the US has a long history of manipulating and overthrowing democratically elected governments, a practice certainly made easier when the CIA or NSA have access to the complete communications of the politicians (or candidates). That's certainly an 'existential threat to democracy', just not the one you vote in (with some nominal power to exercise 'oversight' over such agencies).

Fixnum

13 năm trướcdiscuss

Something like http://scratch.mit.edu/ ?

Fixnum

13 năm trướcdiscuss

Out of curiosity, what's wrong with Unison?

Fixnum

13 năm trướcdiscuss

I was involved in marking a standardized test for high school students and one question involved inventing a story on an (unspecified) election. What shocked me the most, aside from the poor writing ability, the unintentionally unbelievable facts of the stories, and the surprising amount of confusion and internal contradiction within the students' responses, was that although remarkably few students demonstrated much awareness of politics or the political process, despite having taken a mandatory course on this subject, nearly all of the students regarded voting as a mystical or near-spiritual experience of civic involvement, social communion, and individual empowerment.

Some students were probably 'sucking up'. But nearly every student?

Fixnum

13 năm trướcdiscuss

Google didn't exactly invent the self-driving car - they basically bought the Stanford team and some people from CMU and elsewhere.

Fixnum

13 năm trướcdiscuss

It's funny you mention these two books in the same comment, since I always assumed Landau was one of the targets of Sussman and Wisdom's comment, "It is surprisingly easy to get the right answer with unclear and informal symbol manipulation." (See their paper, Functional differential geometry.) Sussman/Wisdom's book is, from a brief look, not 'rigorous' either, but the 'symbol manipulations' in Landau/Lifschitz's series are sometimes borderline insane!

Fixnum

13 năm trướcdiscuss

The soon-to-be-released GHC 7.8 (Haskell) can defer type errors until runtime to allow you run your program even if part of it is broken, and you can also add "holes" in place of an arbitrary expression and the compiler will tell you the type of the expression you need to replace it with (of course, this will explode if run). I suspect GHC's error messages are better than Ocaml's as well.

Fixnum

13 năm trướcdiscuss

> I'd concentrate first on building internally consistent mental models.

I strongly agree -- and the Lisp/REPL combination is extremely helpful. Specifically, I believe a Scheme-based approach is the best way to learn programming, even if you eventually decide to migrate to something less fortunate like Javascript or Python ... in under an hour from your first exposure you can be thinking about stuff rather than the syntax of loops. I won't attempt to justify the pedagogical reasons for this choice here.

Specifically, I'd recommend (1) using Racket, a "batteries-included" Scheme derivative with a simple IDE/debugger, and either (2) Concrete Abstractions (free at https://gustavus.edu/+max/concrete-abstractions-annotated-to...), or (3) the upcoming book Realm of Racket (coming in May), which will cover some of the same CS 101 material as well as GUI and distributed programming via writing games in Racket. (There is an earlier book called Land of Lisp but I feel its environment (CLISP) and coding practices are rather baroque.)

Depending on your student's interests you could simultaneously look at some web programming (plenty of HTML/CSS material is available from Mozilla, Google, etc.; there's an upcoming Udacity course on HTML5 game programming), lower-level stuff like assembly, arduino, or whatever.

Hope this helps.

Fixnum

14 năm trướcdiscuss

A number of relevant disclosures are listed at http://www.salon.com/2010/12/24/wikileaks_23/ .

I don't know how one could argue that, e.g., releasing cables showing the Afghanistan war is "unwinnable" (a la Daniel Ellsberg), showing the deep hypocrisy and corruption of many governments (e.g., the Saudi rulership), and the bullying of all sorts of governments into falling in line with American military and economic interests isn't a "good".

If there haven't been any visible policy changes by the US government, then perhaps it's because such a change is not easily to connect directly to Wikileaks. Of course, it could be that Robert Gates is correct in saying claiming that consequences for US foreign policy (from the leaked diplomatic cables) have been "modest". If true, that is unfortunate, but surely not the fault of Wikileaks?

Fixnum

14 năm trướcdiscuss

Roughly speaking, CPUs are highly optimized for sequential execution, with long pipelines, high power consumption, and complex implementations of arithmetic/logic instructions (I'm not an expert, but I _believe_ these are much _better_ than on GPUs, except possibly for certain graphics-related GPU primitives), but relatively few threads. GPUs are optimized for parallel execution, and run many more threads than CPUs, each with higher latency, but nonetheless with higher overall throughput.

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Online draft of "Parallel and Concurrent Programming in Haskell"

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The girl who conned the Ivy League

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Colourblindness cured in monkeys by gene therapy

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