> usually work correctly after they compile
I still don't buy in to this trope.
Q: What is true of every single bug in production?
A: It passed both your type checker and your tests.
I still don't buy in to this trope.
Q: What is true of every single bug in production?
A: It passed both your type checker and your tests.
My bugs got past my type-checker, but only 100 of them. You have 1000 because the 900 my type checker caught, your dynamic language didn't. Then you go and write unit tests for them, and spend a day writing code that my compiler generated automatically for me.
My reasoning in no way implies that. I simply said that I'm sick of this argument that "if it compiles, it works!" Nobody who knows what they are talking about actually believes that, especially not people who design and build statically typed languages!
Each of those would likely have been a runtime error in a language like Python.
Just earlier today, I had to write a short Python script (I normally write Go), and I was bitten by this. I'm used to the compiler telling me up-front when I try to concatenate a string and an integer, or when I misspell a variable name.
Yes, there are other ways around this (and proofreading your code before you write it is a good practice, in addition to tests). But static typing can make development much faster[1].
Even if you claim that you would have caught all of those bugs in unit/integration/system tests (which I simply don't believe - no real-world project has test coverage that's that good), it's much better to catch bugs at compile-time, because (unless you're writing C++) your tests take much longer to run than your code does to compile.
[0] I qualify this to rule out C, which has weak typing as well as memory management issues to complicate things, and Java, which just has a terrible type system period.
[1] In some sense this is all a moot point, because any difference in development speed and/or code correctness between statically-typed and dynamically-typed languages is dwarfed by one's familiarity with the languages in question. The only real way to test this directly would be to use a statically-typed language that allows disabling of all compile-time type checks as a compiler flag or pragma, but few languages do this in a way that'd be straightforward to do a meaningful blind test.
Each of those would likely have been a compile time error in a language like Haskell.
Just earlier today, I was writing some C++ (I normally write Clojure) and I was bitten by this. I'm used to evaluating code in the REPL as I work, telling me up front when I try to concatenate a string and an integer, or when I misspell a variable name.
Yes, there are other ways around this (and proofreading your code before you write it is a good practice, in addition to tests). But dynamic typing can make development much faster[1].
Even if you claim that you would have caught all of those bugs in a type system (which I simply don't believe - no real-world project has types that are that precise), it's much better to catch bugs at run-time, because (unless you're writing Go) your compiler takes much longer to run than your REPL does to eval.
[0]: I qualify this to rule out Python, which has weak typing as well as mutability issues to complicate things, and JavaScript, which just has a terrible REPL period.
[1]: In some sense this is all a moot point, because any difference in development speed between statically-typed and dynamically-typed languages is dwarfed by one's familiarity with the languages in question. The only real way to test this would be to use a dynamically-typed language that has an optional type system as an external tool, luckily quite a few languages do this in a way that'd be straightforward to do a blind test (Typed Racket, Typed Clojure, Erlang w/ Dialyzer).
Never mind that not even Python or Ruby, and especially not JavaScript, provide sensible useful REPLs with sane code reloading semantics.
People who shit on crappy type systems turn around and then shit on crappy REPLs in broken dynamic languages. I'd take a statically typed language over a language with a bad REPL any day.
And so does Scala...
I dunno, I have 11 years of python experience, and almost a year of haskell experience. I am more productive in python when doing small (<100 lines) scripting type tasks. But I am noticeably more productive in haskell when writing bigger things. Haskell has a relatively crappy web ecosystem, yet I'm still more productive with snap+postgresql-simple+digestive-functors then I have ever been with any python framework (from zope way back in the day to django and flask). Tasks that are more skewed to haskell's strengths like highly concurrent network servers make the difference even more pronounced.
Why do you consider this a hindrance? Haskell has a lot of issues, but that's really not one of them. You can write a Haskell program and be relatively confident that it's going to work right in a way you simply won't be with, eg, Java. And you don't have to wait until compiling. With ghc-mod and vim/emacs configured, you'll be notified upon saving if you blew up something in the current file. You don't need to run your code in a REPL to find out about it, although GHCi is pretty good. You spend a lot less time figuring out what goes wrong at runtime, although I'll grand you that the tooling is poor enough that you have a bad time doing when it happens.
> I qualify this to rule out Python, which has weak typing
Excuse me? You rule out Python due to weak typing and mutability but disqualify Javascript due to its REPL? This must be sarcasm. I have no comment about Javascript's REPL (which one? node's?), but Python is most certainly not weakly typed, not in the way "weak typing" is commonly understood. As for mutability, they are comparable (except that Python has at least the good grace to throw an exception at runtime if you attempt to access an attribute which does not exist).
The try/fail/modify/repeat cycle of REPL-driven-development is what appeals to me. I "get" the value of strongly typed languages, but I'd prefer to opt-in to strictness, rather than have it forced upon me.
Other than for quick scripts I have no interest in dynamic languages now, fully converted to the Typed side ;-)
Ruby and Scala are quite similar in some ways: terse syntax, functional, MOP capable (implicits), mixins (traits), etc., but yes, you have to prove to the type checker that your intentions are correct/sound.
BTW, Go is not that strongly typed. It seems Google engineers don't like strongly typed languages.
One can write Scala the same way in a Scala shell.