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> 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 typ

> 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.

NickPollard 13y ago
That's a tautology. By that reasoning, don't bother writing any tests, because all your bugs in production will get past them anyway! 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.
- grey-area 13y ago
  If you can provide statistics on bugs being an order of magnitude higher in dynamic languages to back up your figures here, it would be a far more convincing argument. I'm sure type safety catches a few bugs and prevent some from being made, but does it catch as many as you think?
- brandonbloom 13y ago
  > By that reasoning ... 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!
chimeracoder 13y ago
Look at it the other way. In fact, you can do a blind test. Try writing in a strongly, (well[0]) statically-typed language for a while, and count the number of times your code fails to compile due to a type error. 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.
- brandonbloom 13y ago
  Look at it the other way. In fact, you can do a blind test. Try writing in a strongly, (well[0]) dynamically-typed language for a while, and count the number of times your code fails at the REPL due to a type error. 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).
  - vilhelm_s 13y ago
    You can have a REPL in a statically typed language too---Haskell has one.
    - brandonbloom 13y ago
      GHC's REPL wraps all expressions in a giant do-block with an IO monad. It's practically useless without the meta-language of the colon commands. That said, truly modern versions of GHC have deferred type checking for REPL use, which is impressive, useful and, ultimately, a simple emulation of a dynamic language. 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.

> 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.

NickPollard 13y ago

That's a tautology. By that reasoning, don't bother writing any tests, because all your bugs in production will get past them anyway! 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.

grey-area 13y ago
If you can provide statistics on bugs being an order of magnitude higher in dynamic languages to back up your figures here, it would be a far more convincing argument. I'm sure type safety catches a few bugs and prevent some from being made, but does it catch as many as you think?
brandonbloom 13y ago
> By that reasoning ... 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!

chimeracoder 13y ago

Look at it the other way. In fact, you can do a blind test. Try writing in a strongly, (well[0]) statically-typed language for a while, and count the number of times your code fails to compile due to a type error. 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.

brandonbloom 13y ago
Look at it the other way. In fact, you can do a blind test. Try writing in a strongly, (well[0]) dynamically-typed language for a while, and count the number of times your code fails at the REPL due to a type error. 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).
- vilhelm_s 13y ago
  You can have a REPL in a statically typed language too---Haskell has one.
  - brandonbloom 13y ago
    GHC's REPL wraps all expressions in a giant do-block with an IO monad. It's practically useless without the meta-language of the colon commands. That said, truly modern versions of GHC have deferred type checking for REPL use, which is impressive, useful and, ultimately, a simple emulation of a dynamic language. 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.