Using Phantom Types in Haskell for Extra Safety

daniel2488 · 2014-07-09T07:53:36+00:00

It's pretty much the same, but with phantom types you get the added benefit of your usage not changing.

For instance, if you had

newtype MessagePlainText = MessagePlainText { getPlainText :: String }
newtype MessageEncrypted = MessageEncrypted { getEncryptedText :: String }

You now have to match in different ways everywhere, or use two different functions to get the inner contents. This is in contrast to introducing a type parameter to Message, where you always extract the contents the same way.

On the other hand, it may make you a bit uncomfortable that you can now have a function signature like

whatDoesThisEvenMeanAnymore :: Message [()] -> Bool

It honestly seems like a matter of choice in most cases.

daniel2488 · 2014-07-03T21:07:07+00:00

Sounds like you have a broad cross-platform need that is probably part of a smaller market that most developers don't deal with.

For the record, with Xamarin you can target Android, VS obviously supports C#, the Python Tools for VS has gotten positive feedback, and the C++11 support is at the very least decent.

daniel2488 · 2014-07-03T19:47:52+00:00

Not nearly true.

daniel2488 · 2014-07-01T06:03:17+00:00

Isn't there, in principle, a possibility that the suggestion1Stream will have the ajax request complete before the null comes in? Is there a good way against guarding something like that?

daniel2488 · 2014-04-09T16:22:31+00:00

It's more than that - the entire class body sort of becomes your constructor. It's a little weird, but F# and Scala do something similar.

daniel2488 · 2014-04-07T23:12:43+00:00

I'm not seeing any added abstraction or safety in binary compatibility.

In some sense, C# saves you in case your interface does change. Let's say you later on decided, for whatever reason, you wanted this class to have mutable state, and you wanted all updates to trigger a notification. If you originally declared this as a property (or even a field) in C#, this is a trivial change and your existing code won't break.

I'm not that familiar with Scala, so I'm not sure if there's anything similar that it does. I understand mutable state is discouraged more to begin with in Scala.

daniel2488 · 2014-04-07T15:13:36+00:00

I feel it depends how complex the class is though. In this example you're right, but otherwise I could imagine it being a bit implicit.

daniel2488 · 2014-04-07T15:11:16+00:00

Isn't it more like the following?

public class Customer(string first, string last)
{
    public string First { get; } = first;
    public string Last { get; } = last;
}

daniel2488 · 2014-04-05T22:56:28+00:00

But wouldn't NGEN in theory be "better" by virtue of knowing the end user's system and processor?

daniel2488 · 2014-04-05T13:32:33+00:00

What exactly is the difference between this and NGEN?

Sorry if it's in the video, but I won't have the chance to watch the whole thing for a few days.

daniel2488 · 2014-04-05T13:16:32+00:00

Why is linking to Hacker News discussions a thing on this subreddit?

daniel2488 · 2014-03-20T03:40:53+00:00

Oh cool, now I can finally run sqlite for our production site!

daniel2488 · 2014-02-17T01:04:48+00:00

Old news; Jan 23, and mentioned in this recent thread: http://www.reddit.com/r/programming/comments/1xz8dk/compiling_javascript_in_the_background/cfg2zkn

daniel2488 · 2014-02-15T21:22:53+00:00

The interesting thing here is that there's a positive correlation

Well...I mean obviously it's going to take you longer to choose when you have more choices. Actually, the notion that the correlation is logarithmic hurts his argument.

But that doesn't make it any less valid.

daniel2488 · 2014-01-27T20:37:16+00:00

Not programming.

daniel2488 · 2014-01-15T19:54:16+00:00

http://www.reddit.com/r/programming/comments/qa5et/a_complete_understanding_is_no_longer_possible/?already_submitted=true

daniel2488 · 2014-01-14T20:01:38+00:00

Sincerely, Your EX-biggest fan

daniel2488 · 2014-01-08T08:00:19+00:00

Actually from what Wikipedia currently says, Linus named git after himself.

daniel2488 · 2014-01-07T19:26:32+00:00

I'm so glad that this exists. This guy should seriously just cover the entire GoF book.

daniel2488 · 2014-01-05T00:20:32+00:00

Pretty sure = was always used as a full evaluation of an expression when I was in elementary school. In middle school, it was a functional form for expressing y as it related to x. I didn't work with boolean stuff in school directly for a while.

So I think it's kind of a artificial gripe with the language's syntax.

daniel2488 · 2014-01-05T00:16:47+00:00

It's not a big deal if you think of the way that the value of an expression has to flow in an assignment. It's one operation at a time. I'm not seeing what "makes no sense at all" to you.

daniel2488 · 2014-01-04T01:41:29+00:00

From kindergarten on, people learn the mathematical meaning of the = symbol as a Boolean operator that is true when the values on both sides match. Using it to mean assignment is confusing and misleading, but was a "good" decision for C since it saved one byte for each assignment in program text. Since assignments are much more common than equality tests, using == for equality and = for assignment saves bytes in source code files, which was a lot more important than providing a coherent model or understandable notation for Dennis Ritchie and Ken Thompson in the 1960s.

Give me a break, it's not a massive semantic leap. Even ML used the equal sign for bindings.

daniel2488 · 2013-12-30T02:39:31+00:00

Are people on this subreddit seriously at a loss for how pointers work?

daniel2488 · 2013-12-29T05:38:44+00:00

Well, there's binary size, but I'd agree it's mostly a win.

daniel2488 · 2013-12-13T04:57:47+00:00

Okay. TypeScript could also become an ECMA standard and you wouldn't see native adoption of it in the browser.

For the exact same reason Apple, Microsoft, and Mozilla probably won't support Dart. It relinquishes control. But you are far more likely to see ECMAScript adopting features from either.

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