6 ms·

Is it still so easy to maintain Clojure code given it's lack of types? (I know about Typed Clojure; it doesn't seem to have won the hearts of all Clojurians)

by platz 13y ago

Is it still so easy to maintain Clojure code given it's lack of types? (I know about Typed Clojure; it doesn't seem to have won the hearts of all Clojurians) (Or, do you just test the bejezus out of the thing?)

lkrubner 13y ago
I add :pre and :post assertions to most of my functions, so I know the type of everything coming in, and also what is returned. An example of a function that saves a document to MongoDB: (defn persist-this-item [item] {:pre [ (map? item) (= (type (:item-name item)) java.lang.String) (= (type (:item-type item)) java.lang.String) (if (:created-at item) (= (type (:created-at item)) org.joda.time.DateTime) true) ]} (let [item (if (nil? (:created-at item)) (assoc item :created-at (tyme/current-time-as-datetime)) item) item (assoc item :updated-at (tyme/current-time-as-datetime)) item (assoc item :_id (ObjectId.))] (mc/insert "tma" item))) So this function needs to be given some kind of map, and it needs to have 2 keys, :item-name and :item-type, and both of these need to be strings, and if :created-at is already set, then it needs to be a Joda DateTime. It's not accurate to say that Clojure has no types. It just gives you some flexibility about how strict you want to be. I find that Clojure strikes a perfect balance: its flexibility with types allows me to easily integrate a lot of 3rd party tools without much work, but when I need to I can be as strict as a I like with types. Edit to add: wow, the code is ugly on Hacker News. Funny that this site provides no tools for posting code snippets, given the subject.
- deleted 13y ago
  [deleted]
- thinkpad20 13y ago
  Maybe I'm misunderstanding, but it looks like every time these functions get called, they're type checking their inputs and outputs? That seems like a waste of resources. Why not just write unit tests that ensure that they will always be called with the types you expect (or fail at an earlier step if not)? Identify the places where there might be ambiguity in something's type (e.g. when a JSON blob arrives, it might map a key to a list instead of a dictionary, or if a function might return multiple types, etc), and use unit testing to ensure that the type you expect will emerge from those places, or else a failure will occur.
  - Tobani 13y ago
    I believe :pre and :post conditions only get run when assertions are enabled. There are other languages that have this feature (Eiffel touts it pretty heavily), but I haven't seen the AHA! example where this is the long lost feature I've been missing. But that said, :pre/:post w/ unit tests seems pretty powerful. You can assign the invariants to the functions themselves and have a better / more robust set of assertions in your unit tests.
    - thinkpad20 13y ago
      If it only will get run in some sort of testing mode, that's fine I suppose. Although the other drawback to this sort of thing is that it seems to really decrease readability. Most of the time when you're reading code, you just want to see what's actually happening, and having a big messy set of type assertions would be noise 90% of the time (especially because unlike type signatures in Haskell, say, there's no syntactical difference that would allow syntax highlighters to help you visually see what's actual code and what's type assertions).
      - Tobani 13y ago
        So I wouldn't confuse invariants w/ type assertions. Clojure does have separate type assert/checking in core.typed. Yes one thing you might use :pre/:post for is type checking, but it can do more than just that.
        thinkpad20 13y ago
        Right, but unit tests do that too. And that would still be something I would in most cases rather handle in unit tests than in assertions in the code itself, for mostly the same reasons.
        rapala 13y ago
        How do you write a unit test that tries to assert that no one calls the function sqrt with a negative integer? Because that is precisely the case where pre-conditions can help.
- vasquez 13y ago
  I like Clojure, but this looks rather painful. If you're dead set on adding type declarations, perhaps you'd be better off with Haskell or something?
  - MrBuddyCasino 13y ago
    I agree, this looks terrible. It seems every discussion about static vs. dynamic typing on HN ends with the following realizations, spread over multiple comments: - its hard to safely refacture without static types (and the help of the IDE that often comes with it) - dynamic languages must compensate the missing type checking support from the compiler with additional unit tests, negating the productivity gains Sometimes it would be nice to have both worlds in the same language, but the way Clojure does it does't appeal to me at all.
    - Mikera 13y ago
      I'm actually trying to address this in my current language experiment: https://github.com/mikera/kiss https://github.com/mikera/kiss The idea: add static types to Clojure without compromising on the dynamism / flexibility / convenience
- sampo 13y ago
  > "Funny that this site provides no tools for posting code snippets" Indent code by at least 4 spaces. (Just like in Markdown in e.g. Stack Overflow.) like this and indent some more
tsm 13y ago
Tests, core.typed, prismatic/schema, and/or pre- and post-conditions. It's still saner than, say, Ruby.
- Argorak 13y ago
  FWIW: "What does this take and what does it return?" is rarely a question that comes up in Ruby for me. In most codebases, thats a pretty easy question. For others, Clojure wouldn't help at knowing whats going on ;).
tel 13y ago
That was what drove me away from Clojure in the end. It's fun to write, but a challenge to write in such a way that you can read it later without jumping all over the place.
- cryptolect 13y ago
  How big/complex were your functions? Have you seen the style guide? It's easy to write really powerful, nested functions in Clojure, which are damn hard to read the next morning. Taking advantage of thread-first and thread-last macros can really help here. I've finally started to use them heavily. For instance, you could do the following to read a file, parse it from json, and retrieve somekey: (:somekey (cheshire/parse-string (slurp "/tmp/somefile.json") true) Or (-> "/tmp/somefile.json" (slurp) (cheshire/parse-string true) (get :somekey)) In other words, there's much nicer ways to write maintainable, readable code that you can still understand in the morning. Your "jumping around" comment also makes me wonder how you were laying out your functions? My advice is to go through the libraries of the popular Clojure libraries, you will discover a lot of good practices. It's taken me a few months of Clojure to start writing cleaner, readable code.
- airfoil 13y ago
  I had the exact opposite experience. I found that I was laser focused on a particular chunk of code when working in Clojure. Functions were logically grouped together. I never found myself jumping around.
beat 13y ago
Frankly, Clojure doesn't need the intense levels of testing that OO languages require, due to immutability. There's a great deal less forking of possible states to examine. I have a friend who is a strong typing devotee who has worked heavily in Clojure for a couple of years, and he curses the lack of strong typing - but he's comparing to the likes of Haskell and OCaml. As a dynamic typing enthusiast myself, I'm comparing to Ruby, and Clojure is definitely superior in terms of how much it needs to be tested. What drew me to Clojure over Ruby, though, was actually a matter of data modeling. I'm working with a graph database (Neo4J), and I found that good graph technique is terrible OO technique. I was violating the Law of Demeter constantly, reaching through objects to get to other objects, passing internal state around with the express intent of mutation, etc. Switching to a functional paradigm lined up perfectly with good graph design. No more smells! No more pain! And again, a lot less testing, because I'm no longer fighting against the nature of my data.
- Flow 13y ago
  I think you mean static typing, not strong typing.
  - beat 13y ago
    Yep, my bad.
fiatmoney 13y ago
One of the really great things about having rich built-in data structures and a more-or-less purely functional data model is that it's really easy to express transformations and be confident that they work. In Java it's incredibly verbose to express & manipulate something like "a list of pairs of sets of integers" because if that was part of your core data model, you'd want to represent it in a class, and then you have all sorts of problems about what callers expect vs. what they get (e.g., do I get a reference to the original, or a copy? Can I safely mutate this?). But if you actually have facilities to pass around and manipulate those kinds of data structures in a way with no side effects, it's trivial to verify (first on the REPL, then in your unit tests) that whatever transformation you're writing applies properly down the entire nested chain, and it will always work for anything of that pattern. And it is much quicker to write those kinds of transformations iteratively in a dynamic language than trying to represent it on a type level a la Scala.
- beat 13y ago
  That's a good point. A lot of what I built classes and objects for in other languages can really be expressed as simple maps, hashes, lists, and vectors, and more complex types built from them. Clojure's elevation of maps/hashes/vectors to first-class types puts it above Lisp, imho, and its functions to manipulate said data structures are better even than languages like Ruby and Python. I can't imagine having to go back to Java collection classes again. Ugh.
  - lispm 13y ago
    You are saying hashes, vectors, etc. are not first-class types in Lisp? Strange...
- auvrw 13y ago
  but just in case someone considering clojure is worried about missing something like haskell's typeclasses (or whatever they're called in scala), it's worth mentioning that clojure does have some notions of "protocols" and "datatypes" that seem pretty similar.
  - 13y ago
_halgari 13y ago
Many times the clojure code is so much simpler, a) even basic testing will catch most of the bugs and b) there are less bugs since the code is so dense. In many ways it's just simpler to understand what 5 lines of Clojure code are doing, than 50 lines of C# code. On top of all that, sane defaults like immutable data, lack of mutable locals, and sane concurrency primitives means that a whole class of bugs just don't exist in normal Clojure code. All this sums up to a codebase that really doesn't need static typing. I write Clojure code for a living, and have worked on some really large Clojure codebases, and yet I've never felt the need for a type system. It's a fallacy that large systems have to be so complex that only a type system will save you. Often the better route is to simplify and modularize the system.
cryptolect 13y ago
I use prismatic/schema which can be used to define schemas and either validate on demand, or always-validate function inputs. Very useful and easy to add.

by platz 13y ago

lkrubner 13y ago

I add :pre and :post assertions to most of my functions, so I know the type of everything coming in, and also what is returned. An example of a function that saves a document to MongoDB: (defn persist-this-item [item] {:pre [ (map? item) (= (type (:item-name item)) java.lang.String) (= (type (:item-type item)) java.lang.String) (if (:created-at item) (= (type (:created-at item)) org.joda.time.DateTime) true) ]} (let [item (if (nil? (:created-at item)) (assoc item :created-at (tyme/current-time-as-datetime)) item) item (assoc item :updated-at (tyme/current-time-as-datetime)) item (assoc item :_id (ObjectId.))] (mc/insert "tma" item))) So this function needs to be given some kind of map, and it needs to have 2 keys, :item-name and :item-type, and both of these need to be strings, and if :created-at is already set, then it needs to be a Joda DateTime. It's not accurate to say that Clojure has no types. It just gives you some flexibility about how strict you want to be. I find that Clojure strikes a perfect balance: its flexibility with types allows me to easily integrate a lot of 3rd party tools without much work, but when I need to I can be as strict as a I like with types. Edit to add: wow, the code is ugly on Hacker News. Funny that this site provides no tools for posting code snippets, given the subject.

deleted 13y ago
[deleted]
thinkpad20 13y ago
Maybe I'm misunderstanding, but it looks like every time these functions get called, they're type checking their inputs and outputs? That seems like a waste of resources. Why not just write unit tests that ensure that they will always be called with the types you expect (or fail at an earlier step if not)? Identify the places where there might be ambiguity in something's type (e.g. when a JSON blob arrives, it might map a key to a list instead of a dictionary, or if a function might return multiple types, etc), and use unit testing to ensure that the type you expect will emerge from those places, or else a failure will occur.
- Tobani 13y ago
  I believe :pre and :post conditions only get run when assertions are enabled. There are other languages that have this feature (Eiffel touts it pretty heavily), but I haven't seen the AHA! example where this is the long lost feature I've been missing. But that said, :pre/:post w/ unit tests seems pretty powerful. You can assign the invariants to the functions themselves and have a better / more robust set of assertions in your unit tests.
  - thinkpad20 13y ago
    If it only will get run in some sort of testing mode, that's fine I suppose. Although the other drawback to this sort of thing is that it seems to really decrease readability. Most of the time when you're reading code, you just want to see what's actually happening, and having a big messy set of type assertions would be noise 90% of the time (especially because unlike type signatures in Haskell, say, there's no syntactical difference that would allow syntax highlighters to help you visually see what's actual code and what's type assertions).
    - Tobani 13y ago
      So I wouldn't confuse invariants w/ type assertions. Clojure does have separate type assert/checking in core.typed. Yes one thing you might use :pre/:post for is type checking, but it can do more than just that.
      - thinkpad20 13y ago
        Right, but unit tests do that too. And that would still be something I would in most cases rather handle in unit tests than in assertions in the code itself, for mostly the same reasons.
        rapala 13y ago
        How do you write a unit test that tries to assert that no one calls the function sqrt with a negative integer? Because that is precisely the case where pre-conditions can help.
vasquez 13y ago
I like Clojure, but this looks rather painful. If you're dead set on adding type declarations, perhaps you'd be better off with Haskell or something?
- MrBuddyCasino 13y ago
  I agree, this looks terrible. It seems every discussion about static vs. dynamic typing on HN ends with the following realizations, spread over multiple comments: - its hard to safely refacture without static types (and the help of the IDE that often comes with it) - dynamic languages must compensate the missing type checking support from the compiler with additional unit tests, negating the productivity gains Sometimes it would be nice to have both worlds in the same language, but the way Clojure does it does't appeal to me at all.
  - Mikera 13y ago
    I'm actually trying to address this in my current language experiment: https://github.com/mikera/kiss https://github.com/mikera/kiss The idea: add static types to Clojure without compromising on the dynamism / flexibility / convenience
sampo 13y ago
> "Funny that this site provides no tools for posting code snippets" Indent code by at least 4 spaces. (Just like in Markdown in e.g. Stack Overflow.) like this and indent some more

tsm 13y ago

Tests, core.typed, prismatic/schema, and/or pre- and post-conditions. It's still saner than, say, Ruby.

Argorak 13y ago
FWIW: "What does this take and what does it return?" is rarely a question that comes up in Ruby for me. In most codebases, thats a pretty easy question. For others, Clojure wouldn't help at knowing whats going on ;).

tel 13y ago

That was what drove me away from Clojure in the end. It's fun to write, but a challenge to write in such a way that you can read it later without jumping all over the place.

cryptolect 13y ago
How big/complex were your functions? Have you seen the style guide? It's easy to write really powerful, nested functions in Clojure, which are damn hard to read the next morning. Taking advantage of thread-first and thread-last macros can really help here. I've finally started to use them heavily. For instance, you could do the following to read a file, parse it from json, and retrieve somekey: (:somekey (cheshire/parse-string (slurp "/tmp/somefile.json") true) Or (-> "/tmp/somefile.json" (slurp) (cheshire/parse-string true) (get :somekey)) In other words, there's much nicer ways to write maintainable, readable code that you can still understand in the morning. Your "jumping around" comment also makes me wonder how you were laying out your functions? My advice is to go through the libraries of the popular Clojure libraries, you will discover a lot of good practices. It's taken me a few months of Clojure to start writing cleaner, readable code.
airfoil 13y ago
I had the exact opposite experience. I found that I was laser focused on a particular chunk of code when working in Clojure. Functions were logically grouped together. I never found myself jumping around.

beat 13y ago

Frankly, Clojure doesn't need the intense levels of testing that OO languages require, due to immutability. There's a great deal less forking of possible states to examine. I have a friend who is a strong typing devotee who has worked heavily in Clojure for a couple of years, and he curses the lack of strong typing - but he's comparing to the likes of Haskell and OCaml. As a dynamic typing enthusiast myself, I'm comparing to Ruby, and Clojure is definitely superior in terms of how much it needs to be tested. What drew me to Clojure over Ruby, though, was actually a matter of data modeling. I'm working with a graph database (Neo4J), and I found that good graph technique is terrible OO technique. I was violating the Law of Demeter constantly, reaching through objects to get to other objects, passing internal state around with the express intent of mutation, etc. Switching to a functional paradigm lined up perfectly with good graph design. No more smells! No more pain! And again, a lot less testing, because I'm no longer fighting against the nature of my data.

Flow 13y ago
I think you mean static typing, not strong typing.
- beat 13y ago
  Yep, my bad.

fiatmoney 13y ago

One of the really great things about having rich built-in data structures and a more-or-less purely functional data model is that it's really easy to express transformations and be confident that they work. In Java it's incredibly verbose to express & manipulate something like "a list of pairs of sets of integers" because if that was part of your core data model, you'd want to represent it in a class, and then you have all sorts of problems about what callers expect vs. what they get (e.g., do I get a reference to the original, or a copy? Can I safely mutate this?). But if you actually have facilities to pass around and manipulate those kinds of data structures in a way with no side effects, it's trivial to verify (first on the REPL, then in your unit tests) that whatever transformation you're writing applies properly down the entire nested chain, and it will always work for anything of that pattern. And it is much quicker to write those kinds of transformations iteratively in a dynamic language than trying to represent it on a type level a la Scala.

beat 13y ago
That's a good point. A lot of what I built classes and objects for in other languages can really be expressed as simple maps, hashes, lists, and vectors, and more complex types built from them. Clojure's elevation of maps/hashes/vectors to first-class types puts it above Lisp, imho, and its functions to manipulate said data structures are better even than languages like Ruby and Python. I can't imagine having to go back to Java collection classes again. Ugh.
- lispm 13y ago
  You are saying hashes, vectors, etc. are not first-class types in Lisp? Strange...
auvrw 13y ago
but just in case someone considering clojure is worried about missing something like haskell's typeclasses (or whatever they're called in scala), it's worth mentioning that clojure does have some notions of "protocols" and "datatypes" that seem pretty similar.
- 13y ago

_halgari 13y ago

Many times the clojure code is so much simpler, a) even basic testing will catch most of the bugs and b) there are less bugs since the code is so dense. In many ways it's just simpler to understand what 5 lines of Clojure code are doing, than 50 lines of C# code. On top of all that, sane defaults like immutable data, lack of mutable locals, and sane concurrency primitives means that a whole class of bugs just don't exist in normal Clojure code. All this sums up to a codebase that really doesn't need static typing. I write Clojure code for a living, and have worked on some really large Clojure codebases, and yet I've never felt the need for a type system. It's a fallacy that large systems have to be so complex that only a type system will save you. Often the better route is to simplify and modularize the system.

cryptolect 13y ago

I use prismatic/schema which can be used to define schemas and either validate on demand, or always-validate function inputs. Very useful and easy to add.