In addition, the hidden assumption is that all static and dynamic typing are created equal, i.e., since Haskell is statically typed and Haskell appears to have caught Python bugs that unit tests did not, therefore Java will catch bugs in a Ruby codebase, C++ will catch bugs in a JavaScript codebase, etc. Of course this assumption is gratuitous. Haskell in particular has a specific sort of type checking that is far different from Java's or C++'s, for instance.

Further, not all dynamic systems are created equal. Ruby, for instance, I think can be shown to require fewer lines of code to achieve similar functionality to, for instance, Java. Fewer lines of code, should in principle mean fewer opportunities for defects. Dynamic languages with metaprogramming features like Ruby's or Smalltalk's should in principle be able to eliminate more code duplication than an environment like C++. This aspect of dynamic languages should be taken into account, again with a statistically significant sample size, and weighed against bugs caught by static typing.

The study is interesting as a preliminary investigation, but the conclusions should have been much more modest, proportionate to both the sample size, in terms of % of production codebases and the extremely important idiosyncratic nature of Haskell vs. other static typed environments. Something like: "The study has shown Haskell's type system will catch some bugs not caught in an otherwise well-covered Python codebase. These bugs could in theory have been caught by unit tests, therefore it is recommended that when using a dynamic language, more care must be taken to cover these types of bugs."

That would have been a more appropriate and modest conclusion, consistent with the data, than the sweeping generalization "You need Static Typing."

I also mention in the paper that it would be beneficial to conduct this experiment using different type systems for the reasons that you stated above.

The argument against static typing that I was testing didn't mention any particular type system nor any particular dynamically typed language, it was a general argument that stated that unit testing obviated static typing. Because the argument was so general and absolute I felt that any static type system that could be shown to expose bugs that were not caught by unit testing would be enough to refute the argument. I was not trying to prove that any type system would catch bugs not found by any unit tested software. The paper also points out that I'm trying to see whether unit testing obviates static typing in practice, in theory you could implement a poor mans type checker as unit tests, but my experiment was focused on whether in practice unit testing obviates static typing.

Finally I believe that my conclusion in the paper was at least a bit more modest than that of the blog post. The lack of apparent modesty in the blog post was caused more by a lack of ability on my part to accurately summarize than an inflated sense of accomplishment and self importance.

I appreciate the clarification. I think now I see better where your emphasis was: the purpose of the paper was to refute an argument, and of course the level of burden of proof is different and far less in that case. I think this misunderstanding on my part is what caused me to call the conclusions 'trivial' -- too strong and dismissive language on my part anyway.

The irony is, you were attempting to do to the unit-testing-is-sufficient argument what I was attempting to do to what I assumed yours was: provide one counter-example to falsify a broad and generalized thesis.

That said, I think I would have liked to have seen your original unit-testing-is-sufficient argument punched up and qualified into something a little more reasonable and real-world. As you stated the argument, it seems like a straw man to me. It seems one could reduce your version of the argument to something like: "Dynamic languages with unit test coverage will always catch errors that statically-typed environments will." And of course this is far too broad and unqualified a statement, and that is precisely why all you needed was one counter-factual to refute it. You didn't even need a handful of Python programs, or 9 or 20 or 100 errors to prove your point. You only needed one, as you stated above. This is why the burden of proof for your thesis was so small, but also why, in my opinion, even with that reduced scope and more modest conclusion, we haven't really learned much.

As someone who has spent most of my career in statically-typed environments and the last 6 years or so mostly in dynamic environments, and also as someone who has made something like the argument you were attempting to refute, I have to say I would definitely never have made such a brittle and unqualified statement as the one you refuted in your paper. To put it more directly, I think I'm probably a poster-child for the kind of developer you were aiming your thesis at, and I don't feel that my perspective was adequately or reasonably represented. More importantly, having looked at the examples given in your paper, I may have learned a bit about the kinds of errors that Haskell can catch automatically that some coders might miss in a dynamic environment, but not much useful to me in my everyday work context.

I think a more reasonable version of the argument, but more qualified and therefore requiring a far larger sampling of code to prove or refute, would be something like: "Programs written in a dynamic language with adequate or near-100 percent unit test coverage, are no more prone to defects than programs written in a statically-typed language with a comparable level of unit test coverage."

I agree this is a very important conversation to have, and again kudos to the work you put in here. Obviously people have strong opinions both directions, and the discussion, however heated at various moments, is an important one, so thanks for this!

It's only in the last two sentences of his "Conclusion" section that he turns the argument around, and here is where he oversteps:

While unit testing does catch many errors it is difficult to construct unit tests that will detect the kinds of defects that would be programatically detected by static typing. The application of static type checking to many programs written in dynamically typed programming languages would catch many defects that were not detected with unit testing[...]

Clearly, this is overbroad. For starters, he should have used "could" in place of "would". And it wouldn't have been a bad time to remind the reader that Haskell's type system differs from those of other statically typed languages with which the reader may be more familiar.

I don't quite agree, though, that the conclusion is "trivial". Maybe I'm just out of touch, but I wasn't aware of a good test of how true the dynamic argument was in practice, as opposed to theory -- particularly claim #2.

"Based on these results, the conclusion can be reached that while unit testing can detect some type errors, in practice it is an inadequate replacement for static type checking."

As I've already pointed out, this seems to me an ambitious and over-reaching conclusion, given the scope of the study.

But, equally important, it is simply an example of something that was already provable. It should be axiomatic that in principle automatically-generated validation like that provided by static typing should in theory be able to catch type errors not caught manually in a dynamic context, either for reasons of human oversight or human error.

In other words, it seems to me that all that has been done here, is to provide a few concrete examples of what was already true and uncontroversial: auto-generated coverage of specific types of validations can be more comprehensive than some human beings will be in some environments and contexts. It has not shown that the perceived benefits of dynamic typing with good unit tests are outweighed by this fact, nor that, statistically-speaking, errors of this type are common enough to warrant a preference of static typing over dynamic typing with unit tests in all contexts.

That assumption isn't hidden, it is made up. By you. The question was "can static typing catch bugs that made it past a decent (and common) test suite". The answer to that can drive interest in static typing, and thus more language with useful static type systems. Just because java has a crappy type system, doesn't mean we should be content with that.

Not at all. The assumption is clearly implied by the conclusion of the study, which makes an unwarranted equivalence of all languages that have 'static type checking':

"The translation of these four software projects from Python to Haskell proved to be an effective way of measuring the effects of applying static type checking to unit tested software."

> Just because java has a crappy type system, doesn't mean we should be content with that.

I don't know what this means. If the study was meant to comprehend such a broad category as 'static type systems,' and from the explicit language of the study, it clearly was, then absolutely Java must necessarily be included. Otherwise, the study, as I noted, should have restricted its conclusions to a scope of Haskell vs. Python, with at most modest and well-qualified statements regarding the broader implications of static vs. dynamic in general.

No it doesn't. Read what you quoted, it says nothing even remotely resembling "this benefit applies to all languages with static typing". It is testing static typing, not a specific language. It uses the best static typing system to do so. You are entirely inventing the notion that this must then apply to java.

> If the study was meant to comprehend such a broad category as 'static type systems,' and from the explicit language of the study, it clearly was, then absolutely Java must necessarily be included

No it mustn't. Comparing the best of dynamic vs the best of static is a useful test. Just as nobody is complaining they didn't use a worse language than python, it makes no sense to complain they didn't use a worse language than haskell. You don't draw conclusions about the potential of X by examining the worst example of X possible.

Java was state of the art 20 years ago, but it's definitely not the case any more.

You do not test the potential of something by using the worst possible example of it. The only point of your desire is to reinforce the strawman that java = static typing. A test of "do airbags help prevent deaths" would be a very poor test if it used anything other than the best possible airbag technology.

And also, even if you carefully put a layer of explicit typechecking between the reflection based code, and the statically typed stuff, you're still throwing out the Java generics typechecking since none of that exists at runtime, and so your ArrayList<String> can mysteriously contain non-String types when you finally access it.

With that in mind, I agree with davesims that the conclusion in the blog post is too strong. It is: "The application of static type checking to many programs written in dynamically typed programming languages would catch many defects that were not detected with unit testing" I say it is too strong because the author has not bent over backwards to make clear that this conclusion only applies to the "best" type systems, like Haskell.

For the record, I like the study, and once I run the author's conclusions through my bend-over-backwards-filter, I find them interesting. I upvoted this article. I also upvoted davesims' post because it is academic-reviewer level feedback.

So? Folks don't use the "potential", they use the real. They're asking questions like "should I use Java or Python".

> do airbags help prevent deaths" would be a very poor test if it used anything other than the best possible airbag technology.

That's not how things actually work. You decide between what's available. The performance of the best possible airbags is irrelevant. The real question is the cost and benefits of airbags that are likely to be deployed.

The question the study was asking was not "what language should I use for my lowest-common-denominator workforce" but rather "can a static type system catch more errors than unit tests and can statically typed code be as expressive as dynamically typed code".

In other words, it was asking for existential quantification: "does there exist some type system such that..." rather than "forall type systems..." or even "forall average systems...".

Haskell is real.

>They're asking questions like "should I use Java or Python".

That's wonderful, but it has nothing to do with the subject at hand, which was the question "can static typing reduce the number of bugs?". If you want an answer to a different question, don't complain about the answer given for this question, go find someone answering the question you want answered.

>That's not how things actually work. You decide between what's available. The performance of the best possible airbags is irrelevant. The real question is the cost and benefits of airbags that are likely to be deployed.

Why can't anyone follow a simple line of reasoning without resorting to fallacies? He tested the best airbags available. Not theoretical airbags that don't exist. He tested a car with the best airbags available to one without. The airbags were a benefit. You and the other guy making up fallacies insist that this isn't a fair comparison, because you want to drive a car where the airbags deploy 5 seconds after impact. Your crappy car isn't relevant to the question of "can airbags save lives".

Indeed. The conclusion C was out of scope with the premises A and B. C is wrong, but that doesn't mean A and B cannot infer useful, more modest conclusions.

What I don't understand about every one of your responses is that you seem to think false equivalence applies in only one direction.

You seem to think it's fine for OP to infer broad conceptual conclusions from a small subset of the domain, but counter-examples to the broad claims cannot be applied, according to you, because, rather bizarrely you continue to insist that the counter-examples are too specific and and don't apply because the scope is general? That doesn't even make sense.

It's quite simple. OP claims "unit testing is not enough," "you need Static Typing" and uses broad language like "static type systems." I continually insist that such conclusions are out of the scope of the data given: The fact that type-related bugs were found in a handful of relatively small Python programs translated to an idiosyncratic environment like Haskell cannot possibly infer something so broad as what the OP is claiming.

Using Java/C++/Clojure/C#/etc. vs JavaScript/Lisp/Smalltalk/Ruby to give a counter-example is clearly within the scope of the argument. If OP had claimed something like "Python shows risk of static type errors, exposed by Haskell port" and claimed something like "more care and unit-testing is needed to guard against certain types of type-related bugs" I wouldn't have a problem. But that's not what OP claimed.

Yes, clearly you have some serious issues to work through.

No one claims otherwise. However, that's true of Java's type system too.

> Why can't anyone follow a simple line of reasoning without resorting to fallacies?

I followed your simplistic line of reasoning just fine. It was wrong. Admit that and move on.

Of course you can't, which is how you got there.

The biggest obstacle to Haskell becoming more popular is its advocates.

And, it will never replace Java, C, Python, or even PHP. (One of my professional goals is to never use Java.)

What do you mean by that?

Many people, including myself, have had Haskell replace Python.

You are wrong, admit it and move on. Oh gee, does that not actually make a constructive argument?

>The biggest obstacle to Haskell becoming more popular is its advocates.

What does this have to do with anything?

>And, it will never replace Java, C, Python, or even PHP

It already has. You might be too foolish to take advantage of that fact, but how does your foolishness matter to me?

> It already has.

Oh really? Significantly fewer systems are being developed in those languages? How about some evidence?

What? You meant that a couple of applications have been written in Haskell instead of those applications? That's not "replace".

Which reminds me - if I find an application that was written in Haskell that is being replaced by an implementation written in some other language, would you claim that said other language is "replacing" Haskell? If not, don't make the mirror-argument.

It doesn't use the best dynamic language or best unit tests.

Nope.

> The best unit tests is entirely irrelevant

I can find errors in programs with a spell checker. Suppose that those programs have unit tests. Do you really think that spell checker is better than unit tests?

That is precisely what it says, and that is reiterated later:

"...the conclusion can be reached that...in practice [unit testing] is an inadequate replacement for static type checking."

I'm not sure what you're reading, but there's no qualifications in the language used here regarding the idea of 'static type checking,' nothing so modest about the scope of the conclusion as claiming it was merely a "useful test" as you put it. It was a sweeping generalization about two very broad and extremely complex categories of languages. Had the conclusions used more moderate language and qualified itself adequately, I wouldn't have a problem. But all that has been shown here, is that in some contexts more care needs to be taken writing unit tests in a dynamic environment to catch some errors that are automatically caught in static environments. That is all that the data warrants.

This is a very strong claim and it's false. The article doesn't say that anywhere. You interpret it that way.

I would hazard a guess that presenting your own interpretation as fact is what brought on those downvotes you complain about below.

I'm under the (perhaps mistaken) assumption that in academic papers people tend to mean what they say and choose their language carefully, particularly in the conclusion section.

If the following are not in fact broad, strong claims about the nature of static and dynamic languages in general, then won't you please explain to me how I should interpret them?

Here are the quotes from the conclusion of the paper (emphasis mine):

"The translation of these four software projects from Python to Haskell proved to be an effective way of measuring the effects of applying static type checking to unit tested software."

"Based on these results, the conclusion can be reached that while unit testing can detect some type errors, in practice it is an inadequate replacement for static type checking."

"Static type checking" and "unit testing" are two concepts. There are numerous concrete implementations of these two concepts. The former is implemented in several languages, including C++ and Java and Haskell. The latter is implemented in several frameworks/tools, such as TestNG and PyUnit.

The article concludes that unit testing, as a technique for discovering and/or preventing defects, cannot wholly replace static type checking.

Apart from mentioning the concrete implementations of abstract techniques that the author used, the article does not conclude anything about the benefits of using specific languages, frameworks or tools.

What you have claimed so far is that:

1. there is a "hidden assumption is that all static and dynamic typing are created equal, i.e., since Haskell is statically typed and Haskell appears to have caught Python bugs that unit tests did not, therefore Java will catch bugs in a Ruby codebase, C++ will catch bugs in a JavaScript codebase, etc."

If anyone jumped to this conclusion, it was you. The only thing I can conclude from the article is that static typing checks such as those implemented in Haskell catch bugs that were not caught by unit testing logic such as that used in Python projects within the study. To conclude anything more I would need the data not present in the article, such as exactly what types of errors we caught or missed, etc.

2. the conclusion of the study "makes an unwarranted equivalence of all languages that have 'static type checking'"

It doesn't. The conclusion about the static type checking vs. unit testing might not be backed by enough solid data, but the conclusion makes no claims about languages, beyond specifying which languages were used in the study.

3. the claim that "this benefit applies to all languages with static typing" is "precisely what" the conclusion "says".

No occurrence of any phrase even remotely resembling the quote can be found in the article. Saying "this is precisely what it says" means "you'll find that phrase or one very similar to it in the text". Maybe you were trying to claim that "this is precisely what it means", but it's definitely what it "says".

All in all, the sweeping generalization about the concrete languages was introduced by you. My guess is that this is because you were, like me, frustrated by the vagueness of the article. I would have loved seeing more concrete data. Saying "X types of errors were found" is not as good as saying "the following types of errors were found" and that's just the start.

I think the plain, direct language of the paper's conclusion is clear enough without me having to embellish it, and without its defenders extrapolating all of the qualifications and subtexts that they think I missed. You really don't have much to work with, because the paper's clumsy conclusion is small, blunt and unqualified in its scope. It takes a handful of small Python programs translated to an idiosyncratic language like Haskell and concluded:

"in practice [dynamic typing with unit testing] is an inadequate replacement for static type checking."

This is unequivocal language. There's no qualifications about language, context, or any kind of variables that might possibly dilute the strength of the conclusion.

On the other hand, Peter Cooper gives a great example elsewhere on this thread of a much better paper with much broader scope, more stats, and much more modest, qualified conclusions. This is the kind of language that is useful and gives me confidence that the authors didn't start out with an axe to grind and merely followed what metrics they had to the warranted conclusion, no more, no less:

"Even though the experiment seems to suggest that static typing has no positive impact on development time, it must not be forgotten that the experiment has some special conditions: the experiment was a one-developer experiment. Possibly, static typing has a positive impact in larger projects where interfaces need to be shared between developers. Furthermore, it must not be forgotten that previous experiments showed a positive impact of static type systems on development time."

http://www.cs.washington.edu/education/courses/cse590n/10au/...

The blog post is vague, but the paper (also available at the link) isn't. It identifies the particular errors found.

But so far all of the arguments I'm seeing against using, for instance, Java, are coming from a perspective not advocated by the study. You all have a point -- it's just not the point made by the paper.

Saying that "static typing is better than dynamic typing" is like the former: there exists some static typing system that is better than dynamic typing. Saying that "all static type systems are better than any dynamic system" is like the second. All the paper ever says is the first: "Based on these results, the conclusion can be reached that while unit testing can detect some type errors, in practice it is an inadequate replacement for static type checking." Note how it never claims to apply for all possible static type systems; rather, it just says that tests are an inadequate replacement for type systems in general (i.e. there exists some type system that catches more errors than tests). This is exactly like my first example.

In summary: a being better than b does not mean that all a is always better than all b. Just because static typing is better than dynamic typing does not imply that Java is always better than Python; it merely implies that some statically typed language is better than Python.

Generalizing any comment to all static type systems is silly: there are language like C that have a static system but provide basically no additional safety at all. You can easily provide examples of really bad statically typed or dynamically typed languages, but these examples say nothing of static or dynamic typing in general: they're just bad. Questions about static vs dynamic typing can only be answered by the best (or at least good) examples of each.

Showing that a good statically typed system is more robust than a good dynamically typed system is a useful proxy for comparing static typing to dynamic typing. This is similar to a study on seat belts ignoring poor seat belts that strangle the passengers in the event of a crash.

In short: just because static typing is better does not mean all static type systems are better, because you can always come up with a sufficiently bad example of static typing.

That is precisely my point. You are saying "this comparison of coke vs pepsi is no good because they used cold coke, and when I drink warm coke it isn't very good". Yeah, no shit. Stop drinking warm coke. Your decision to drink warm soda has no bearing on the test of cold soda vs cold soda.

Fine, then don't claim something like "All cokes in all contexts at all temperatures are better than all pepsis in all contexts at all temperatures."

This is equivalent to what the study does with static vs. dynamic. Your argument, if you actually had a point, would be something along the lines of, "wait I'm talking about this boutique hand-crafted cola (Haskell) I get at Whole Foods, not that old Coke (Java), that's 20 years out of date!"

You're trying to retro-actively reduce the scope of a study you didn't write. The conclusions clearly use generic language that brings all static typed languages into a comparison with all dynamic languages. The false equivalence is not mine! It's the study's. If you want it differently, go write your own study that reduces the scope of the conclusions.

Help me out here -- since the study confines itself to a handful of small Python programs translated to an idiosyncratic language like Haskell, how can the scope of the study possibly in any way qualify as a study on something so broad as "the concept of static vs. dynamic typing"?

Are you not confusing a better, more appropriate argument you'd make for the argument actually made in the paper?

EDIT: > Sure, it left that open as a possible interpretation for people looking for justification of a preconceived notion, but you can't really blame that on the authors.

Is that really an argument you want to make, that I can't blame an author for using broad and imprecise language that infers unwarranted conclusions in an academic paper?

You raise a good objection here. Is it possible to draw conclusions about the class of type systems labelled "static typing" vs dynamic typing by using a small sample of programs? I think this is where the impedence mismatch is occurring. The author seems to take static typing to mean "what can be currently accomplished through static typing", and thus he was justified in using the strongest static type system in use to do the study. Taking it this way, then the study seems meaningful.

Taking the other meaning, the class of type systems labelled static typing, then you end up with a very large set of languages each with (perhaps) varying amounts of power. Doing a study with just one static language does seem inadequate. Although, depending on the class of errors caught, it may still be valid. As far as I've seen, Haskell doesn't catch new classes of errors that are impossible in other systems, it just makes it a lot easier to do so. So essentially Haskell has the same power as other common type systems. If this holds, then the study would still be valid. (Admittedly I know very little about Haskell so I could be completely wrong).

TLDR: I see what you're saying, and I do agree that there needs to be more said before his conclusion can be supported by the study.

He could only compare one of the best possible environments for writing dynamically typed code and unit tests to one of the best possible environments for writing statically typed code.

He didn't. He said "coke tasted better than pepsi". I've explained this to you several times already. You are the only one saying anything about "all the time in every context". You. Not the author, not his paper. You.

I do think that a rational argument can show it, but my argument is too long to fit into the margin.

After over ten years working in dynamic languages I'm very happy to have a compiler on my side again.

I spend most of my time these days fixing bugs and regressions due to the sheer scale of the project, and I'm a running meme at work for saying "a type checker could have caught that!". I can't imagine going back to a dynamic language now.

I was very surprised to discover that my Scala code was a lot easier to understand and maintain and had fewer bugs.

I think what I enjoy most is the type system though, and the ability to make massive refactorings until stuff compiles. 9 times out of 10, things just work after that.

That said, I'm currently hacking on a compiler to see if I can come up with a design for a static language that's almost as pleasant to use as a dynamic one, so I'm not completely hopeless. But it certainly seems like the data point that until now no such superior type system (strict but flexible) has become widely popular should not be underestimated.

These days it's mostly C++/Obj-C but I'm keeping an eye on Haskell for iOS.

Really? Is that even possible? Can't imagine Apple being okay with that.

that's basically the design criteria behind Go's type system.

[1]: http://existentialtype.wordpress.com/2011/03/15/boolean-blin...

My problem with Go is that it does not have sum-types and pattern-matching. This means that branching (conditionals) in Go do not gain any type-information. And that means that programmers have to manually keep track of the invariants that hold true in each of their conditionals, and if they get them wrong, they get no help from the compiler.

If a whole program has 1 bug due to being implemented with dynamic types over static types, and that bug has gone unnoticed, then it can't be particularly important.

The other common proposition is that dynamically typed languages are faster to write in than statically typed languages. If this is true then we need to compare the saving in development time with the cost of the bugs which go undetected.

My gut feeling says that this line of analysis is never going to prove that static typing in inherently "better".

This part is also very tricky, as most of people's hard-earned experience with this is (almost by definition) old. In recent years, type inference has reduced the type-caused slowdown immensely. E.g. in Haskell you can (+) write large statically typed programs without specifying any types at all - they are inferred by the compiler.

(+) But please don't.

ML way is to not write type annotations unless they're needed, not that I agree with it, but it certainly works in some way.

I used to work on .NET, and you'd have to program against crazy, non-intuitive patterns in order to have your code "clean" (I hated IoC containers as well as writing all that boilerplate code for Attributes. And for Java, remember that hilarious post about Factory-Factory-Factory patterns http://discuss.joelonsoftware.com/default.asp?joel.3.219431?)

I'm not saying statically typed languages are bad. Type errors always bite me the ass in Ruby, but it's a small price to pay (IMO) for better maintainability.

EDIT: By the way, it sounds like I'm an ignorant dynamically-typed lover. I'm not, I still yearn for those type safety net, but I'm just speaking from a pragmatic perspective.

     I hated IoC containers as well as writing all
     that boilerplate code for Attributes

My static language of choice is currently Scala. It is less verbose than both C# and Java (for example you never have to generate setters/getters). Also, whenever I work with Java I always work with projects such as Lombok / Guava.

And I have no need for "IoC containers". This is partly because of Scala, but also because of the libraries I'm using. Currently I'm using DropWizard for the development of web services, which is just a thin wrapper around Jetty + JAX-RS. Because the resources (commonly known as controllers in MVC frameworks) are configured as instances (not classes specified in web.xml), then IoC is easy because you are free to do the bindings yourself.

IMHO, the necessity for IoC containers in C# / Java has risen from poorly designed frameworks. So you may not have a choice in the matter, however using something like Google Guice in combination with Scala is much nicer, because of Scala's mixins in combination with structural typing.

I used to feel just like you did (at the asp.net 1.x) days. I went to Ruby on Rails for awhile. But once NET 2.0 (generics/nullable types) and then 3.5 (LINQ), I was hooked on C# again. We also have the dynamic type now.

I want the features a statically typed language gives me with minimal boilerplate.

It's hard to give up IDE features like "find everyplace this method is called" and know that you found all of them (disregarding reflection, etc and assuming private methods).

Visual Studio will do this type of thing for Python now. We aren't terribly far away from having the benefits of both.

I really like python as a scripting language. I just don't feel as good about scripting languages in big projects as I do a modern language like C#. (Just my humble opinion, no science).

But when I have to move from Rails to, say, ASP MVC (which is quite good, btw), generics are actually one of my biggest frustrations. Even with some of the quasi-dynamic typing available in C#, and even though I believe I have a pretty strong grasp of advanced generics concepts (in? out? Generic methods? Wildcards? Argh!) to me they introduce a maddening level of conceptual complexity and un-readability that are simply not worth the trouble.

I consider Ocaml [1] to fill that particular niche. When I was going through my FP phase, I tried that out a little before going full-on lazy evaluation with Haskell.

From what I can recall, the type inference isn't as cool as what's in Haskell, but at least it's there. There are plenty of libraries, and packages for major OSs.

[1] http://caml.inria.fr/ocaml/

In retrospect, I think I was also thinking about type-classes in Haskell, which Ocaml does not have. But from what I understand Ocaml has other means to achieve the same ends.

Removing inheritance would have made the language (and every other language, too) a lot easier, but seeing that people cope with C# or Java quite well I'm not sure about the merit of the "complex" claim.

Comparing the C# and the Scala spec is very enlightening, even though they have different writing styles of course (so I won't bother bringing up page numbers).

Checking and realizing which "features" are in one language, but not in the other, is very helpful to gain some insight into this topic.

What do you think?

My main criticism is that it allows too much syntactic flexibility.

Scala does have problems. But NOT the language. I find the language to be extremely elegant and well designed.

The problem lies with the community. I find Scala libraries to be an abomination of taste and common-sense. I don't know why that is, but in general I stay away from libraries commonly used by Scala developers.

For instance I prefer JUnit over ScalaTest, I prefer JAX-RS (DropWizard) over Scalatra or Play. I prefer Maven over SBT.

Of course, you could say that the language itself invites this nasty style of programming, because the syntax is too flexible and the features too powerful. However I strongly disagree.

For instance I've worked with a lot of Ruby and Python libraries over the years and most popular Ruby/Python libraries are extremely well designed, easy to use and easy to look under the hood. Ruby on Rails for instance was not pretty, however starting with version 3 it went through a major refactoring effort and now the codebase is clean and easy to follow; while being one of the easiest to use and full-featured web frameworks ever built.

Unfortunately when picking a language, you do have to rely on a community and an ecosystem of libraries. However in the case of Scala, if you don't like the style of the current community, you can just pick from the thousands of already available and mature Java libraries.

http://blog.goodstuff.im/yes-virginia-scala-is-hard/

You can use a subset that's easier, however the usage of the more advanced language features need a level of understanding that's beyond the capabilities of many developers.

And this is in fact true of most mainstream languages. Java may be an easy language to learn, but Java isn't just a language, but a platform - and as soon as beginners start messing around with multi-threading (since multi-threading capabilities in Java are in your face), then all hell breaks loose ... from this point of view, Scala may in fact be easier to deal with than Java is for beginners.

And for instance I see people complaining about the method signatures exposed by the collections API. I can't read those signatures very well myself, however in the case of a dynamic language, such as Ruby, you'd have to look at the source-code to see what the method actually returns. So IMHO, even if those signatures are complicated, at least you've got signatures to look at.

Scala requires a more disciplined mindset. David Pollak actually developed Lift in response to problems he had managing big Rails projects so I don't think he would be advancing this analysis if he didn't think Scala was harder than Python/Ruby.

In my experience a lot of those "I programmed 15 years in Java, get off my lawn" senior developers get angry about Scala. This is interesting, because it isn't that way for other languages running on the JVM like Clojure, JRuby or Groovy.

It is only a speculation why it is like that, but in my opinion it is because alternatives like Groovy, JRuby, Clojure are considered to be some sort of "supplemental" or "add-on" languages by those people, while Scala is seen as full-scale alternative to Java (not in the sense that it will replace Java, but in the sense of "I can write 100% of my application in this language without dropping down to Java for the performance critical parts").

I think it is interesting how different the reaction is compared to C# <> F#, for instance. Is it because Java and C# developers come from different backgrounds? Because F# is "made by Microsoft", while Scala is not "made by Oracle"? Is it because Java developers were happy with Sun telling them that they wouldn't need all those "fancy" features of the .NET languages? I think this would be interesting to discuss further, although I think it is hard to come up with valid data points.

From my experience, most of the claims about "complexity" and "too hard for beginners" come not from people learning the language, but from people with > 5 years of Java experience _not_ wanting to learn another language.

I'm quite ambivalent about the syntactic flexibility. On the one hand, they cut it down for 2.10, but on the other I think it is a superficial measurement. There are a lot of languages with more flexibility and a lot of languages with less, both seem to be alive and well. (Just want to make it clear that I think your stance is totally valid, even if I disagree slightly. Different people have different tastes, and this is a good thing!)

Once you get a hang of them, writing in any modern statically typed declarative language enters you into a state such that code flows out effortlessly. It is a wonderful feeling.

Most (but not all) of my pain slinging Java come from misuse of XML and design patterns. Now we're on to services (SOA). Yippee. It's just a socket, marshaling, retry logic. Does it really need its own ecosystem of consultants, conferences, and books?

Java the language could be more terse with type inference, string literals, default visibility modifiers, and some other syntactic sugar. (I'm pretty optimistic about Ceylon as a successor.) But 18 years on, for the most part, I'm still very pleased with Java. Except autoboxing and annotations; garbage.

Java the platform (JDK, J2EE, java.util., collections, javax., misc APIs) should be burned to the ground, plowed under, and complete do over. And any one who says "factory method" gets keelhauled.

But your personal experience is comparing expressive languages to unexpressive languages, and then making the mistake of thinking you are comparing dynamically typed languages to statically typed languages. What does .net's ugly (in your opinion) API have to do with static typing? Factory-Factory-Factory patterns is a joke even in java, but it also has nothing to do with static typing at all.

>By the way, it sounds like I'm an ignorant dynamically-typed lover. I'm not

Well, you are repeating the most commonly used and easily debunked strawman, so it really does sound like ignorance. Have you used a modern statically typed language? If not, by definition you are in fact ignorant.

A perfect example is QuickCheck. QuickCheck allows you to write complicated tests very simply by relying on the type system. You just write out the invariant and the type system automatically figures out which random generators to use to run the tests.

QuickCheck has been ported to a bunch of other languages, but it's more complex and seems harder to use in dynamically typed languages as compared to Haskell.

A simpler example in the same vein is Haskell's read function. Essentially, read is the opposite of toString--it goes from a string to some value. The beauty is that you never need to specify what type you're parsing; it can figure out what type it needs to be thanks to the type system. So instead of having a bunch of functions like parseDouble and parseInt, you have a single read function. This also makes the library prettier by maintaining the symmetry between show and read (toString and fromString).

    (    Bugs found by unit tests (     ) Bugs found by type-checking    )

I'm glad someone spent a lot of time trying to answer this question, but I don't think it will affect my choice of language in any new project. I like to write code in the languages I like, and bugs be damned.

1. A common argument is that static-typed languages slow development. I'm not touching that land-mine.

If you claim type-checking is free, the counter-argument is not that it "slows development." The counter is that type-checking is not free because it incurs measurable costs. You may sacrifice dynamic features, you may have to add declarations and type casts-- these are all costs whether they "slow development" or not.

(Simple solution: don't waste time trying to claim type-checking is free and just focus on the benefits.)

To get as close to the land-mine as I am willing: I like C. I like Python. I like Ruby. But most of all, I like using the right tool for the job.

But it is also untrue that you have to "add declarations and type casts". With type inference, you don't actually have to.

Though the original commenter did follow-up, clarifying that the common interpretation of "free" doesn't closely match the point he'd intended to make

Someone was asking me about my thoughts on static vs dynamic. And I realized that I have two reasons for my tests a) I didn't do something stupid like mistype a method or variable name and b) validate my logic.

Sometimes I think it swings 20/80 and others 80/20. But either way, I know that's why I gravitate towards integration tests in Ruby, and that some of them would go away if it were statically typed.

Even after coding in Ruby all these years, I'm still just as afraid of (and susceptible to) problems in a).

b) Second, I'm going to argue that tests are actually free. And I think this because I don't care how good static type proponents think they are, I know they don't wait until it compiles and SHIP SHIP SHIP, they actually run their damned program. The alternative to automated testing is manual testing, not no testing.

> The alternative to automated testing is manual testing, not no testing.

Actually, unit tests have different costs than manual testing. That doesn't make them free. For example, with unit tests, you now have more (possibly buggy) code to maintain.

Well, that's no problem. Just hit them with a bunch of unit tests...

( Bugs found by unit tests ( ) Bugs found by input validation )

Or in other words...

String s = "lastname'; drop table user--";

...is still a perfectly acceptable string.

It seems to me that type checking is the simplest form of validation (are you an int, are you a String) and nothing more. It wont tell you if that int is positive or negative or if that string is an email.

When dealing with either static/dynamic languages I think more unit tests should be spent validating.

So you're saying it is impossible to do this without static typing?

It's entirely possible to do this without static typing. It's impossible to guarantee that all database calls use a Query instead of a String without running the code in some form.

...oh wait, right before it is sent to mysql it is turned back into a string again.

My point is that static typing doesn't help you do anything other than verify that the objects being passed are of a particular type. I'm not saying static typing is bad or good I'm just saying that type checking itself is NEARLY USELESS unless you include some sort of validation.

		Query q = new Query("select * from users where id = (id)");
		QueryParam qp = new QueryParam("(id)",25);
		q.addParam(qp);
		ResultSet rs = q.execute();
		public class Query {
			public ResultSet execute() {
			for(QueryParam qp : this.getQueryParams()) { 
				this.getSql().replace(qp.getId(),qp.getValue());
			}
			super.execute(sql);
			}
		}

But if you write a secure version, you only have to write it once. You only have to maintain it in one place. You only need to test it in one place. And if you forget to use your secure Query type, anywhere else in your code, the compiler will yell at you. It's a significant advantage.

This is easier to see in a language with a rich, flexible and expressive type system than it is in Java. The writer of the original article used Haskell for a reason.

> You only have to maintain it in one place.

> You only need to test it in one place.

Again, so this cannot be done in a dynamic language? If it can be done, why bring them up?

> And if you forget to use your secure Query type, anywhere else in your code, the compiler will yell at you. It's a significant advantage.

The only thing the compiler will yell at you is if you passed a type that is not of a Query type. The compiler will not yell at you for getting the current session directly or creating your own jdbc driver for that matter.

In Haskell, I'd have a module, Database, that held all my db code. That module would export functions something like

query :: Query -> DBResult update :: Query -> DBAction -> DBResult

(read those as "query is a function that takes a Query and returns a DBResult.")

In the rest of my program, those functions would be the only way to talk to the database. There's your guarantee.

Could I, rather than using my nice database module, instead drop into IO and write code to do something vicious? Surely. But now we've moved beyond bugs and into active malice.

> "Again, so this cannot be done in a dynamic language? If it can be done, why bring them up?"

It's harder. With duck typing, if it looks like a Query it is a Query, no? Even if it drops your table. I'm no expert on dynamic languages, and I'd believe that there are sophisticated object hierarchies that can do these things (at runtime...), but the original article is empirical evidence that real projects get this wrong.

Really, though, try a language with a modern type system and see for yourself. I know we Haskell users sound like zealots, but the difference between the Java and Haskell type systems truly is night and day.

    //Bad Person
    username = "lastname'; drop table user--"
    
    //Good Programmer
    query = "select * from users where name like %[username]%";
    input = {"username":"frank"};
    result = execute(query,input);
    
    //Bad Programmer
    query = "select * from users where name like '%"+username+"%'";
    result = execute(query, {});
	

    //Bad Person
    String username = "lastname'; drop table user--"

    //Good Programmer
    Query q = new Query("select * from users where name like %[username]%");
    Input input = new Input(username);
    q.addInput(input);
    Result r = q.execute();
    
    //Bad Programmer
    Query q = new Query("select * from users where name like '%"+username+"%'");
    Result r = q.execute();
    
	
	

You're building a new query string each time you create a Query object, and concatenating the string onto that. With that approach, each time you build a Query object you have a fresh opportunity to mess up. So you're right that there's no difference between your to cases.

Let's drop my off-the-cuff example and look at how a real library, postgresql-simple, handles the issue:

  query :: (ToRow q, FromRow r) => Connection -> Query -> q -> IO [r]
 

  query conn "select x from users where name like ?" (Only username)

Notice that because Query is a distinct type from String, just doing

  query conn ("select x from userse where name like" ++ username)

The full documentation for postgresql-simple is here: http://hackage.haskell.org/packages/archive/postgresql-simpl...

  User.select('x').where('name like ?', username)

query conn ("select x from users where name like #{username}")

How do type-safe languages prevent this?

  query conn ("select x from users where name like " ++ username)

Longer explanation: I suspect the syntax is a bit confusing, since while I keep saying "select ..." is a Query, it looks an awful lot like a String. Here's what's going on. Haskell has a typeclass called IsString. Query is an instance of IsString, as is String.[^2]

Quoted text can represent any instance of IsString. So the compiler sees a function that expects a Query and an IsString of some sort, and through the magic of type inference, it decides that the IsString must be a Query.[^3] And when you try to use a function that concatenates Strings on that Query, it knows that Something's Not Right.

[1]: Haskell doesn't have string interpolation. But if it did, this is how it would work.

[2]: And other instances as well. postgresql-simple actually uses ByteStrings, not Strings, for performance.

[3]: I've fuzzed the evaluation order a bit, for simplicity. In practice the first error reported might be that you've passed 2 arguments to a function that expects 3.

On the dynamic side, Rails (in Ruby) doesn't currently catch SQL injections, but it does catch HTML-escaping injections. It (roughly) tags all strings as tainted by default, and when you send them to the browser, it escapes them. If you want to send literal ampersands, angle brackets, etc., you have to mark them as explicitly safe. Since most of your literal HTML is generated by templates (which themselves distinguish variables from static HTML), you end up with run-time safety unless you actively try to break out of it.

To make a safe query type you'd have to provide non-string primitives to build one, if I understand correctly. You can't allow just a full query string (with all of the injections already in place) to be converted to a Query type (as in his Bad Programmer example).

Of course you can make sure you never actually run the bad query with dynamic typing. I assumed it was obvious when talking about static typing that the difference would be compile time vs run time. With a statically typed language, when you make the error, you get told about it by the compiler. With a dynamically typed language, you find out about the error later, when that code actually runs.

I never suggested that...?

> With a statically typed language, when you make the error, you get told about it by the compiler. With a dynamically typed language, you find out about the error later, when that code actually runs.

> static typing enforces that you always use that function, and can't forget and accidently submit an unescaped string to the database.

So you are really just saying "static typing requires you to use static typing". This has nothing to do with actually writing good code or having any sort of validation. Just that the compiler tells you that you are sending the wrong type... that's what we are arguing about?

Look my whole point is static typing by itself gives you next to nothing (See my code example below) without some form of validation beyond static typing. That obviously holds true to dynamic typing as well... I'm not even sure what we are arguing about.

You mean like the validation you get when you compile a program?

Yes, a statically typed program that never gets checked is strictly worse than a dynamic program, but that's the whole point of the type system: you can check it. This argument is a strawman because nearly every language with a static type system includes a validation step (maybe Dart is an up-and-coming counterexample).

Yes, you did suggest that. I am not sure how this level of cognitive dissonance is possible. What possible purpose does your example serve then if it doesn't impart any sort of meaning at all?

>I'm not even sure what we are arguing about

Clearly. Please, take the time to think through the subject and present a clear point that you will not later pretend you didn't make.

The example shows that static typing doesn't do anything more than what it says. It doesn't solve problems/fix bugs or provide some magical insight to the system as you seem to believe.

I'm genuinely curious as to your position and why you are so... clearly opinionated. I'll take the "idiot banner" for today. Please provide me with your insight as to what the fundamental argument (and why you feel so strongly about it) really is.

A) How to define the Query type such that it would convert injection bugs to type-checking errors (No, it cannot simply be a function from a full String containing a query to a Query type, as you demonstrated).

B) Sure, you could define the same Query primitives to do the same in a dynamically typed language. The main difference is that the type-checking errors due to incorrect use of the query primitives would be caught at runtime.

As for A, you would want to define primitives that build query strings safely. That is: Query(unsafe_string_here) wouldn't work. Either because it allows too much (still can inject the original string) or disallows too much (escapes everything, makes the query invalid).

Instead, you would define "select", "update" and other querying primitives as non-string primitives you can use to build queries. You would basically mirror SQL or the query language you use into non-string primitives that allow constructing safe queries.

B) Yes, you could do this with dynamically typed languages. Right before executing your query you would need to do an isinstance() check or some other way to validate that the query was generated using the safe machinery. This means no duck typing. If you allow other, unsafe implementations of the query type here, you get the unsafety back.

It's hard to even come up with an example, but consider testing that an HTML generation library doesn't unexpectedly emit text unescaped. The pile of tests you write if you're in Python or Perl mostly translate to Haskell unscathed, in that each individual test still is testing something ("is the href attribute on <a> encoded properly? is the name attribute on <a> encoded properly? ..."), yet considered as a whole the tests have significant redundancy with the type system, because if you set the types up correctly there's a great deal fewer possible ways to screw up than there used to be.

Also, rereading my comment, something that may not be clear, when I said "some non-trivial percentage of the tests are still redundant to the type system", I mean per test. On each test, some non-trivial percentage is actually redundant, not that there is some percentage of tests that are totally redundant. You just remove those, of course.

The use of type-checking doesn't negate the need for unit tests. It just adds another layer of validation. The Unit Test "cost" is still there.

For example, taken to the extreme, you can write 0 tests in Agda, and still have more assurances about correctness than if you had 100% coverage in a dynamically typed program.

In Google, in my project, we've had runtime errors in Python code, due to wrongly spelled variables(although that is a different problem), and type error, something a compiler would have caught.

Strong type checking is something that I truly like about Haskell and OCaml, I'm reasonably convinced that once my program has passed the typechecker, it is logically correct. Though debugging in Haskell is truly a different ballgame altogether (I'm a Haskell noob).

I'll stop here lest this turns into a flame war.

As another example, Java may let you get NullPointerException, but FindBugs detects a lot of those.

Depending on your editor of choice, you can get integrated pyflakes/pyling/flake8, e.g. I use vim and the syntastic plugin which is great.

This way, you get a bit of on the fly static checking without needing to remember command line tools/using vcs hooks, which is much more productive.

Thanks again.

  > we've had runtime errors in Python code, due to [...]
  > type error, something a compiler would have caught

Personally, I think that people tend to obsess about the specific type of errors because the 'solution' (static-typing) is something that already exists, whereas there is not easy solution to other types of flaws.

Missing imports and redundant imports also go away.

Lots of lots of invariants in the program can be encoded as types, too, so any bugs relating to them go away too.

When you want parallelism, you get useful guarantees about not changing the deterministic result you had before you added parallelism.

I used to use Python, but after Haskell, there's no way I'd go back...

  > "NoneType has no attribute '...'"

This may be something that Haskell doesn't allow, but it's not something inherent to static-typing.

But I totally agree, static typing is no cure for a wrong program. With power/expressiveness also comes a great ability to goof up.

On top of this, the C type system is not really about correctness at all. My understanding is that it primarily helps with performance, memory management (e.g. you know the size of stuff) and not accidentally using a non-pointer as a pointer. I'm not a C person, but C does not give off a vibe of caring about correctness.

In fact, C is particularly unsafe: you can get all sorts of fun things like bus errors and segfaults that are basically impossible in other languages. C definitely has a place, but only if correctness is much less important than performance.

You can ultimately come up with a sufficiently bad language for anything.

Also, the way Haskell avoids null errors like this is with the static type system. So while it's certainly not inherent to all static type systems (then again, nothing has to be inherent to static type systems except being verified at compile time), it is a property of the type system.

My original point was that it's possible that we (programmers) focus more on issues that could be with static typing (of some implementation) just because it seems like a group of problems that could be 'easily' solved. I.e. 'the grass is always greener'

The problem with C is that nullability is not statically typed.

    I'm reasonably convinced that once my program has passed the typechecker, it is logically correct

Just as you should write good tests, that actually test for useful properties, so you should write good types -- and get useful proofs back from the compiler as a result.

[1] Isn't the old joke in Haskell "If your program compiles it probably does something someone would find useful, but not necessarily the useful thing you want"

Your point taken, but that is a problem in programming language X, which has Y type system, for all permissible values of X and Y.

Also, the author responds to a similar point in his comments: http://evanfarrer.blogspot.com/2012/06/unit-testing-isnt-eno...

The point is, these were real-world codebases with substantial unit tests, and they had type errors that weren't caught by these unit tests.

Honestly, in several groups I've worked with, I've had trouble getting people to add unit tests even to code in dynamic languages. A codebase which already has substantial unit tests is likely to be better than average, on that basis alone.

This is about saying, in the messy real world, do unit tests actually make type safety obsolete. And the answer is, no, they don't, even code with fairly good test coverage can be improved by adding typechecking. Now, there is the question of whether writing in the dynamic language allowed people to write code faster (it's generally a lot easier to translate correct code once it's written than to write it in the first place); or whether some of the more highly dynamic features of dynamic languages benefit writing or deploying code.

"Dynamism (computing), When any process in computer is using Dynamic management methods for its processing/computing/memory management/parallelism handling for being able to give more user friendly work that are more easy to interact and modify."

... for whatever that's worth.

  staticity
  staticness
  statism

I (the author) would like to address both of these. First of all I completely agree that more research needs to be done. I mention this in the paper. I have provided a data point not a proof. It took me a couple months of several hours a day to the do the translation, I hope more people translate more programs to see if the results hold in the face of a larger data set. Second I agree the quality of the Python code isn't that great. I wanted to see whether unit testing obviated static typing in practice. In order to avoid selection bias I choose the projects at random. I picked the first four projects that were < 2000 lines of code and that had some sort of unit testing.

I believe that my methodology, nor my conclusions are flawed but that all should remember that a single experiment does not make a scientific proof. I hope that others will try to replicate this experiment on many more code bases. If they do it will be interesting to see the results.

  * KLEE: Unassisted and Automatic Generation of 
    High-Coverage Tests for Complex Systems Programs  
    http://llvm.org/pubs/2008-12-OSDI-KLEE.html
  * Erlang Dialyzer 
    http://www.erlang.org/doc/man/dialyzer.html
  * Datalog based systems 
    http://www.cse.msu.edu/~cse914/Overheads/mmcgill-java-static-race-detector.pdf

  * Standard ML / OCaml
  * Haskell
  * Scala
  * Typed Racket
  * Qi

It's like coffee. If your coffee is shitty (complect), then no amount of sugar (unit tests) or cream (type checking) will make it any better.

Though I can guarantee you that either sugar or cream with only 0.1% coffee content will still be usable as sugar or cream for other purposes, so I can't even agree with your analogy taken to its limit: that no amount will make the coffee better, because enough will make it usable for other things.

In fact, unit testing and static type checking are largely orthogonal to the complecting issue that Rich was getting act. Unit testing and static typing will both increase complexity; they are both ways of making assertions about the behaviour of the code, and for working code, they should both actually be redundant. But that doesn't mean, as a practical issue, that we should do away with either or both. We're fallible. Saying the same thing twice or three times increases the probability of finding something inconsistent if our statements are not representative of the Platonic ideal we're trying to express.

Anyway, it occurred to me that with Clojure it could easily happen that I trade bugs caused by state problems to bugs cause by type problems.

With Haskell, on the other hand, you may not need to trade :)

Not exactly this, but there exists "Program indentation and comprehensibility" http://www.cs.umd.edu/~ben/papers/Miara1983Program.pdf which tries to tackle the "2 spaces vs 4 spaces vs 8 spaces indent". Not very good tho, since they seem to add superfluous indent levels like a separately indented "then" after "if" (Pascal), which effectively doubles the actual indent of the semantic block.

On second thought, let's forget about them after all...

That's one thing I really like about go. It's nearly as opinionated about its braces as Python is about its not-braces (almost...).

Put braces where they make the code readable. Use indents instead where they make the code more readable.

And if you do need a rule, make sure it's based on actual need. I.e. start the discussion with "the past two months we've had 4 non-trivial bugs which could have been avoided if we enforced braces.", not have a bunch of people bicker about their Personal Preferences (usually goes by the name "Best Practices").

It also ends the bikeshedding, "that's how we do it there, deal with it".

If they don't respect existing style, you don't have a "lack of rules" problem. You have a lack of education problem. Do code reviews. Point out to Bob that he's making the code less by letting the style alternate.

But you're sort of touching on what I meant when you say you don't want "chaos". If you can point at a code file and say "this is chaotic and hard to read - we could improve that by converging on style X or Y.", then we could come to some agreement.

Personally, I'd rather deal with slight aberrations in style than having a flaming row and angering half my team.

Really inspiring, painstaking piece of work.

  f :: Iterable a => a -> b
  f x = (do stuff with x...)

You're implying that all type-systems derived from HM have a form of bounded polymorphism. They're not, for example OCaml does not have type classes (you could probably encode a lot into objects, though).

http://www.cse.unsw.edu.au/~chak/papers/WC06.html

I believe they're experimental in Coq.

Yeup, some folks did show the functors + modules \equiv type classes in some sense, for system F or a variant thereof. Theres also an oleg approach too I think.

The major differences between type classes and interfaces are: * In Java interfaces the interfaced type is restricted to the first argument (the this). In Haskell interfaces the interfaced type can also appear on return values and arguments. * In Java you need to decide what interfaces to implement when you create your class. Haskell allows interfaces to be implemented for previously existing types. * Java allows for subtyping. You can turn a monomorphic program into a polymorphic one just by creating subclasses while in Haskell you would need to rewrite your code to be explicitly polymorphic.

You're describing an "existential" type.

With dynamically typed languages I find that you still need to worry about types, but you have to trace through the code to figure out what type a particular variable is (esp. if you're not the only one working on a project). In a statically typed language that information is readily available.

When I was learning Haskell, I wrote a program to count the value of a cribbage hand. The code was half the length of an equivalent JavaScript program.

The expressiveness of a language has more to do with the length of a resulting program than static or dynamic typing.

Haskell code is more concise than most dynamically typed languages.

Type inference cuts down the verbosity tremendously.

How so? Java is verbose, but that isn't due to being statically typed, it is just a verbose language. Statically typed languages with type inference are no more verbose than dynamically typed languages.

On the other hand, successful conversion of these codebases is a very interesting result. Apparently static, at least static as sophisticated as Haskell, actually can express most of the idioms in standard python. This surprises me, as I've never seen a C++ program of significant complexity that didn't resort to void*s somewhere.

Who says that? There's trade offs, multitudes, in choosing paradigm / language. It's never so black and white (except for academics, and twits who like to argue more than code)

I did not read paper, don't have time for 60 pages of pointlessness.

http://news.ycombinator.com/item?id=4137283 comes pretty close to making that claim, and that's just on this page.

> "There's trade offs, multitudes, in choosing paradigm / language. It's never so black and white"

Sometimes, it is. Most people don't use COBOL anymore, with reason; better languages came along. Programming is still a new field in the scheme of things. It would be strange if our languages were perfectly optimized, with no room for improvement without offsetting costs.

> "twits who like to argue more than code"

Some of us like to do both :) But go program; we won't stop you...