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>Transducers are composable algorithmic transformations. They are independent from the context of their input and output sources and specify only the essence of

>Transducers are composable algorithmic transformations. They are independent from the context of their input and output sources and specify only the essence of the transformation in terms of an individual element. Because transducers are decoupled from input or output sources, The biggest thing holding me back from learning Clojure is that I fear it will take me a decade to become remotely competent in it.

fnordsensei 11y ago
Don't worry too much if you don't get the esoteric stuff in the beginning. The fact that it's there just means that there's room to grow. The core language is actually very simple and quite straightforward. It just allows for some quite mind-boggling stuff. Try Carin Meier's Living Clojure if you feel up for an intro.
- akilism 11y ago
  2nd for Living Clojure. Great crash course in Clojure for working developers.
  - akilism 11y ago
    Might as well check out Joy of Clojure by Michael Fogus also, really good book.
- puredanger 11y ago
  And then check out the new Clojure Applied (by me) which aims to be a good intermediate level intro. https://pragprog.com/book/vmclojeco/clojure-applied https://pragprog.com/book/vmclojeco/clojure-applied
  - mark_l_watson 11y ago
    +1 I looked at your table of contents: nice topic selection. The free excerpt was a good read. You might edit your comment to provide a direct link to that.
  - jwhitlark 11y ago
    Clojure Applied is an excellent book so far. I've been using Clojure for a long time, and it's still been very helpful in updating idioms for modeling domains, composing applications, etc. I'd say it's required reading for working Clojure programmers, of any experience level. We really needed a "how to build applications in Clojure" to complement all the "how to do stuff in Clojure" books that are already out.
dkersten 11y ago
You don't need to learn every feature to be competent in the language. Some features are advanced features that are not required in day-to-day programming (eg, transients, you can go forever without ever touching them, but if you need performance they're there). A lot of the advanced things are of most interest to library authors.
pron 11y ago
It is one of the simplest and easiest languages around. The addition of transducers is an unfortunate case of Clojure "pulling a Haskell", valuing an elegant abstraction over ease of understanding and learning. Indeed, your comment alone shows that doing them (and especially giving them a high profile) was a mistake. Just because you can abstract something elegantly doesn't mean you should. No beautiful abstraction is worth scaring people away. Fortunately, Clojure doesn't make many such mistakes, and it usually tries to err on the side of pragmatism. I hope transducers aren't the beginning of a trend. But just don't use transducers until you feel comfortable enough with the language. They're not an essential feature.
- kyllo 11y ago
  I don't understand this argument. Clojure shouldn't have transducers because the word sounds scary? Programming language designers should avoid adding powerful, higher-order abstractions because they are hard to understand? This sentiment is incredibly anti-intellectual. And like you said, if you don't understand it you don't have to use it.
  - leishulang 11y ago
    Everyone who is learning Functional programming should be able to use map/reduce well. With that, understanding transducers is just natural.
    - pron 11y ago
      Most languages with map/reduce don't have transducers (and they're certainly not central features). Also, don't forget that while Clojure is functional, it is also very much imperative (it's a functional-imperative language rather than a pure-functional language).
      - dragonwriter 11y ago
        > Most languages with map/reduce don't have transducers That's true but mostly irrelevant to the point that transducer usage isn't complex once one understands map/reduce, which are common, whether or not transducers are.
afandian 11y ago
No need. Getting started, and to a level where you can be productive, is very easy. LISP is a very simple language, and lots of the features of Clojure mean that it's simple in practice too. That's compared to Haskell and Scala, which do require a little theory in order to get started. IMHO. There will perhaps come a time, where you want to know about and transducers, but by that time the concepts won't seem intimidating.
markc 11y ago
Actually the learning curve is very gentle, and you can gradually expand from basic features into the more advanced stuff when ready. Many of the Clojure features that have sophisticated underlying design principles (like transducers) can be used cookbook style from easy-to-understandable examples. Jump in, the water's warm.
birdsbolt 11y ago
This is only slightly complicated if you're writing your own transducer operation. What is interesting is that these transducing operations can be written quite generically - code reuse is huge. But, usage of transducers is similar to Java 8 Streams, or Haskell stream fusion, only that the implementation is fully generic, not dependent on the container/source.
astine 11y ago
That's not a very plain-language description of transducers. Transducers are functions which can be applied to any sort of collection or sequence. You can use then to do something like filter a collection or an input stream with the same code. They are basically just a way to make things like 'map' and 'filter' work on datatypes other than sequences, such as streams or channels. http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming http://blog.cognitect.com/blog/2014/8/6/transducers-are-comi...
- susi22 11y ago
  Again, that's not true. Transducers are about reducing things. That's why a transducer first needs a reducing function. But I won't go into details what trasnducers are. There is many good (and long) blog posts about it.
  - astine 11y ago
    No, reducers are about reducing things. Transducers are about creating reducers that can be used on arbitrary collection-like things. Reducers come from the observation that many higher order operations on collections can be built on reduce. You just supply the right reducing function and you get the equivalent to 'map' or 'filter'. This is useful because when you start chaining these higher order functions you can gain performance be replacing the multiple function calls with a single reducer based function. To take the example from the main docs: (fold + (filter even? (map inc [1 1 1 2]))) Here, each function returns a reducer which is a combination of the original collection ([1 1 1 2]) and a reducing function which will be applied to the collection. Ultimately this code will result in a single call to reduce with a single function applied to [1 1 1 2]. This differs from the 'standard' way of doing this: (reduce + (filter even? (map inc [1 1 1 2]))) ...in that no intermediary representations of the collection are necessary. Neat. A transducer takes the same idea, but does it in a way that lets you apply this to arbitrary collection-like things, not just seqs. A transducer works by cutting out the original collection; you build the reducing function by chaining transducers together and pass it later another function which will pick apart the collection-like thing. So: (into [] (r/filter even? (r/map inc [1 1 1 2]))) Becomes (into [] (comp (filter even?) (map inc)) [1 1 1 2]) Which is not exciting until you realize that that middle term can be passed to 'chan' al la: (chan 1 (comp (filter even?) (map inc))) Which means that everything going through that channel will increased by filtered with 'even?'. Now you have a suite of functions which will take a transducer and use it in a lot of different contexts allowing you use the same logic on streams, sequences, channels etc. This same logic, that you would originally have expressed with a series calls to 'map' 'filter' 'take' and applied only to a sequence.
jarcane 11y ago
honestly, I use Clojure 1.7 for work every day and I don't even know what a transducer is. It's easy to overstate the necessity of advanced features, ones very few programmers probably actually use.
- dj-wonk 11y ago
  Transducers are part of cultural drive of the Clojure community to identify common patterns and simplify design. Rich's presentations do a nice job of explaining how a transducer is about separating [how to do the work] from [where the work is done]. By "work" I mean mapping, filtering, reducing, and so on. By "where the work is done", I mean that a transducer doesn't care what kind of data structure it operates on. If you keep this in mind, perhaps re-reading http://clojure.org/transducers http://clojure.org/transducers won't be as intimidating. As a general comment, to those new to Clojure, when you find something in Clojure that seems strange or different, I encourage you to ask "What does [function X] care about? (e.g. need to know)" and "What does [function X] not need to know?". This relentless drive to simplify design and responsibilities mean that functions are small and "opinionated", but in ways that are driven by constraints, not arbitrary decisions. So these choices make a lot of sense -- I'd argue they flow pretty naturally.
  - jarcane 11y ago
    Don't get me wrong; I'm not knocking it. I definitely see the value in these kinds of features. Like zippers, I'm sure it's another case of "If you understand it, it's really useful." The point is, you don't necessarily need it to get the job done, and you certainly don't need to be intimidated about it or feel obligated to learn it right off. Even Haskell isn't actually so difficult to grasp the basics of, if you keep this in mind and just think "Do IO in a 'do' block" and go about your way. See [1]. You don't have to know everything in any language just to get some work done, a lot of times advanced features are just that: advanced, stuff for doing things a bit more efficiently, or to handle certain rough edge cases. Learn them in their own time, and they'll make you better at what you do, but don't get wrapped up too much in expecting perfect efficiency from yourself. A lot of programmers seem to be, as a people, kinda bad at this kind of self-reflection, like we're all sheep in wolves' clothing trying to avoid showing a hint of weakness. I know I sure am. There's nothing wrong with not knowing something, just try and take a moment learn it when you can. [1] http://blog.jle.im/entry/io-monad-considered-harmful http://blog.jle.im/entry/io-monad-considered-harmful
enoch_r 11y ago
If you have an understanding of functions like map, filter, and reduce, transducers are actually pretty easy. Say you have `(map inc [1 2])`. You can run that, and get `'(2 3)`. A transducer is the `(map inc)` part of that call (slightly confusingly, this isn't partial application or currying). You can apply it to something like `[1 2]`, but you can also compose with it, by combining it with say, `(filter even?)` to get something that represents the process of incrementing everything, then removing odd numbers. Or you can put in things that aren't collections, like asynchronous channels, and get back a new channel with the values modified accordingly. That's pretty much it. What I think I love most about Clojure is that there are fantastic, esoteric, academic ideas that, when I read about them in a context like this for the first time, I a) do not understand them, and b) have no idea how they would be useful. Then I read an example or two, and suddenly it's apparent that the tool is really as simple as it can be--there's very little accidental complexity--and is extremely useful.
- deleted 11y ago
  [deleted]
- aoeuasdf1 11y ago
  The way you explain it, it's no different from functions and function composition; in which case, why invent new vocabulary? I do remember looking into them before and translating them into Haskell and they ended up not being identical to functions in the trivial sense that you suggest, but I forget how.
  - arohner 11y ago
    Why have new vocabulary for the state monad? Transducers are mostly function and function composition, but with a specific signature. There are a handful of contracts on a transducer, so it is useful to have a name, so you can say "this function takes a transducer" and "this function returns a transducer".
  - kazinator 11y ago
    Transducers are functions. The thing is that they are functions that are designed to serve as the functional argument to reduce. And they pair with ordinary functions which are not transducers. For instance if we have (map inc [1 2]), there exists a transducer function T such that: (reduce T [1 2]) == (map inc [1 2]) I.e. we can somehow do "map inc" using reduce. Okay? Now, the clever thing is this: why don't we allow map to be called without the list argument? Just let it be called like this: (map inc) This looks like partial application, right? Now what would partial application do? It would curry the "inc", returning a function of one argument that takes a list, i.e.: ;; if it were partial application, then: ((map inc) [1 2]) ;; same as (map inc [1 2]) But Hickey did something clever; he overloaded functions like map so that (map inc) returns T! (reduce (map inc) [1 2]) ;; same as (map inc [1 2]) The cool thing is that this (map inc) composes with other functions of its kind. So you can compose together the transducers of list processing operations, which are then put into effect inside a single reduce, and the behavior is like the composition of the original list processors. It's like a linear operator; like LaPlace. Composition of entire list operations in the regular domain corresponds to composition of operations on individual elements in the "t-domain".
brudgers 11y ago
Clojure is sophisticated [0] but it is hard boiled down to necessary complexity. This means that ordinary language features like interop [1] are well sugared and more abstract concepts like transducers are simple to implement and map well to their description [2]. Stuart Halloway's Programming Clojure captures this idea. [0] and big for practical purposes like Common Lisp. [1] you can get at all of Java perhaps better than you can from Java using the REPL. [2] like lexical scope and continuations in Scheme.
spion 11y ago
Transducers create functions that are meant to be passed to reduce (i.e. take accumulator and element and return a new accumulator). Its possible to implement most other functions (map, filter, take etc.) using reduce. Transducers take advantage of that. Unfortunately, if you try to do that, you'll notice that the implementation is sometimes tied with the way you build the entity: e.g. for vectors, map implemented in terms of reduce would start with an empty vector then append to it. That sucks. We want operation chains that are independent of the data structure they operate on. We want them to work on vectors, lists, channels, whatever - anything that can have a reduce-like operation (anything reducible) However, it turns out you don't necessarily have to recreate the entity (e.g. list) when chaining. All you need to know how to do is invoke the next operation in the chain, i.e. the next reduction function. For example: * map can apply the function on the element to get a new result, then call the next reduction function with the accumulator and that new result. * filter can check the element and either return the old accumulator or apply the next reduction function with the element, etc. Therefore, transducers simply take an additional argument: the next reduction function that should be applied. This lets you build up a chain of operations (e.g. map filter etc) that doesn't care about the kind of entity they're operating on. Only the last "step" must be a reduction function that needs to know how to build the result.
phren0logy 11y ago
You may feel less intimidated by "Clojure for the Brave and True." The landing page features a rodent with an eye patch and a sword. http://www.braveclojure.com/ http://www.braveclojure.com/
- jsilence 11y ago
  > Delete ~/.emacs or ~/.emacs.d if they exist Ehhhh, no!
  - KurtMueller 11y ago
    Hence the emphasis on Clojure for the Brave.
  - ZainRiz 11y ago
    Don't get disheartened. I just started this tutorial last weekend (and had no emacs experience before) and it's been great!
yogthos 11y ago
Clojure is one of the easiest languages to learn. You need to know very few concepts to become productive in it. I get co-op students very 4 months at work and they generally start doing useful stuff within a week or so. I wrote a conceptual starter guide a little while back ( https://yogthos.github.io/ClojureDistilled.html https://yogthos.github.io/ClojureDistilled.html ), that covers all the basics that you need to know to get up and running.
jgalt212 11y ago
Are transducers necessary in Clojure because functions of function of functions (etc...) on immutable data structures execute slowly?
- harlanji 11y ago
  They help relieve pressure on the garbage collector by eliminating intermediate sequence allocations (eg. (comp (map a) (map b) (filter c) (map d)) would create 4 sequences, transducers create none). Consequently you can work with results incrementally unless there is an intermediate flush required such as for a windowed aggregation. I imagine most applications aren't very sensitive to the performance gain, but it's good to know for when you need it. In addition it's a nice and testable, compos-able pattern. I've only done backend work, no cljs yet, but I'd call it reasonable practice to think in terms of compositions/transducers for most data transformation pipelines in the future though, throughout the stack, whether performance matters or not.
tsmarsh 11y ago
Its more like 18 months. Unless you already know a lisp or Haskell. The only thing I can say is that it is totally worth it, I know very few people who regret putting it in their head. The same is less true for Ruby, php, Visual Basic.
nbardy 11y ago
I had a similar feeling when I first starting using Clojure, but I found it was more of a discomfort from discussing programming language with a direct and accurate vocabulary. After a while I've become much more comfortable reading about and watching videos on programming languages in this style and I really enjoy being able to discuss and think about design decisions in a straightforward way.
goldfeld 11y ago
Dive in! It's like beginning ballet over twenty: you'd really have to trust your slow, consistent, building momentum to eventually get you there. Learning Clojure up to getting remotely competent with it did take me a year and a half, during which I used it in all my projects. Also including getting into Emacs. I breathed it all throughout. Now I'm good in it, I have ease designing big FP systems, and I finally decided to learn transducers a few weeks ago and it took me me just an hour to grasp/implement it in my app. Neither a decade :)
jwhitlark 11y ago
Basic competence comes pretty quick, it's a small core language, compared to most. Most things like transducers you can ignore for a long time. The longest part of learning it for me was learning to think functionally, but you can do that in pieces, and nearly all of what you learn is applicable to any functional language, or even imperative languages with functional aspects.

fnordsensei 11y ago

Don't worry too much if you don't get the esoteric stuff in the beginning. The fact that it's there just means that there's room to grow. The core language is actually very simple and quite straightforward. It just allows for some quite mind-boggling stuff. Try Carin Meier's Living Clojure if you feel up for an intro.

akilism 11y ago
2nd for Living Clojure. Great crash course in Clojure for working developers.
- akilism 11y ago
  Might as well check out Joy of Clojure by Michael Fogus also, really good book.
puredanger 11y ago
And then check out the new Clojure Applied (by me) which aims to be a good intermediate level intro. https://pragprog.com/book/vmclojeco/clojure-applied https://pragprog.com/book/vmclojeco/clojure-applied
- mark_l_watson 11y ago
  +1 I looked at your table of contents: nice topic selection. The free excerpt was a good read. You might edit your comment to provide a direct link to that.
- jwhitlark 11y ago
  Clojure Applied is an excellent book so far. I've been using Clojure for a long time, and it's still been very helpful in updating idioms for modeling domains, composing applications, etc. I'd say it's required reading for working Clojure programmers, of any experience level. We really needed a "how to build applications in Clojure" to complement all the "how to do stuff in Clojure" books that are already out.

dkersten 11y ago

You don't need to learn every feature to be competent in the language. Some features are advanced features that are not required in day-to-day programming (eg, transients, you can go forever without ever touching them, but if you need performance they're there). A lot of the advanced things are of most interest to library authors.

pron 11y ago

It is one of the simplest and easiest languages around. The addition of transducers is an unfortunate case of Clojure "pulling a Haskell", valuing an elegant abstraction over ease of understanding and learning. Indeed, your comment alone shows that doing them (and especially giving them a high profile) was a mistake. Just because you can abstract something elegantly doesn't mean you should. No beautiful abstraction is worth scaring people away. Fortunately, Clojure doesn't make many such mistakes, and it usually tries to err on the side of pragmatism. I hope transducers aren't the beginning of a trend. But just don't use transducers until you feel comfortable enough with the language. They're not an essential feature.

kyllo 11y ago
I don't understand this argument. Clojure shouldn't have transducers because the word sounds scary? Programming language designers should avoid adding powerful, higher-order abstractions because they are hard to understand? This sentiment is incredibly anti-intellectual. And like you said, if you don't understand it you don't have to use it.
- leishulang 11y ago
  Everyone who is learning Functional programming should be able to use map/reduce well. With that, understanding transducers is just natural.
  - pron 11y ago
    Most languages with map/reduce don't have transducers (and they're certainly not central features). Also, don't forget that while Clojure is functional, it is also very much imperative (it's a functional-imperative language rather than a pure-functional language).
    - dragonwriter 11y ago
      > Most languages with map/reduce don't have transducers That's true but mostly irrelevant to the point that transducer usage isn't complex once one understands map/reduce, which are common, whether or not transducers are.

afandian 11y ago

No need. Getting started, and to a level where you can be productive, is very easy. LISP is a very simple language, and lots of the features of Clojure mean that it's simple in practice too. That's compared to Haskell and Scala, which do require a little theory in order to get started. IMHO. There will perhaps come a time, where you want to know about and transducers, but by that time the concepts won't seem intimidating.

markc 11y ago

Actually the learning curve is very gentle, and you can gradually expand from basic features into the more advanced stuff when ready. Many of the Clojure features that have sophisticated underlying design principles (like transducers) can be used cookbook style from easy-to-understandable examples. Jump in, the water's warm.

birdsbolt 11y ago

This is only slightly complicated if you're writing your own transducer operation. What is interesting is that these transducing operations can be written quite generically - code reuse is huge. But, usage of transducers is similar to Java 8 Streams, or Haskell stream fusion, only that the implementation is fully generic, not dependent on the container/source.

astine 11y ago

That's not a very plain-language description of transducers. Transducers are functions which can be applied to any sort of collection or sequence. You can use then to do something like filter a collection or an input stream with the same code. They are basically just a way to make things like 'map' and 'filter' work on datatypes other than sequences, such as streams or channels. http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming http://blog.cognitect.com/blog/2014/8/6/transducers-are-comi...

susi22 11y ago
Again, that's not true. Transducers are about reducing things. That's why a transducer first needs a reducing function. But I won't go into details what trasnducers are. There is many good (and long) blog posts about it.
- astine 11y ago
  No, reducers are about reducing things. Transducers are about creating reducers that can be used on arbitrary collection-like things. Reducers come from the observation that many higher order operations on collections can be built on reduce. You just supply the right reducing function and you get the equivalent to 'map' or 'filter'. This is useful because when you start chaining these higher order functions you can gain performance be replacing the multiple function calls with a single reducer based function. To take the example from the main docs: (fold + (filter even? (map inc [1 1 1 2]))) Here, each function returns a reducer which is a combination of the original collection ([1 1 1 2]) and a reducing function which will be applied to the collection. Ultimately this code will result in a single call to reduce with a single function applied to [1 1 1 2]. This differs from the 'standard' way of doing this: (reduce + (filter even? (map inc [1 1 1 2]))) ...in that no intermediary representations of the collection are necessary. Neat. A transducer takes the same idea, but does it in a way that lets you apply this to arbitrary collection-like things, not just seqs. A transducer works by cutting out the original collection; you build the reducing function by chaining transducers together and pass it later another function which will pick apart the collection-like thing. So: (into [] (r/filter even? (r/map inc [1 1 1 2]))) Becomes (into [] (comp (filter even?) (map inc)) [1 1 1 2]) Which is not exciting until you realize that that middle term can be passed to 'chan' al la: (chan 1 (comp (filter even?) (map inc))) Which means that everything going through that channel will increased by filtered with 'even?'. Now you have a suite of functions which will take a transducer and use it in a lot of different contexts allowing you use the same logic on streams, sequences, channels etc. This same logic, that you would originally have expressed with a series calls to 'map' 'filter' 'take' and applied only to a sequence.

jarcane 11y ago

honestly, I use Clojure 1.7 for work every day and I don't even know what a transducer is. It's easy to overstate the necessity of advanced features, ones very few programmers probably actually use.

dj-wonk 11y ago
Transducers are part of cultural drive of the Clojure community to identify common patterns and simplify design. Rich's presentations do a nice job of explaining how a transducer is about separating [how to do the work] from [where the work is done]. By "work" I mean mapping, filtering, reducing, and so on. By "where the work is done", I mean that a transducer doesn't care what kind of data structure it operates on. If you keep this in mind, perhaps re-reading http://clojure.org/transducers http://clojure.org/transducers won't be as intimidating. As a general comment, to those new to Clojure, when you find something in Clojure that seems strange or different, I encourage you to ask "What does [function X] care about? (e.g. need to know)" and "What does [function X] not need to know?". This relentless drive to simplify design and responsibilities mean that functions are small and "opinionated", but in ways that are driven by constraints, not arbitrary decisions. So these choices make a lot of sense -- I'd argue they flow pretty naturally.
- jarcane 11y ago
  Don't get me wrong; I'm not knocking it. I definitely see the value in these kinds of features. Like zippers, I'm sure it's another case of "If you understand it, it's really useful." The point is, you don't necessarily need it to get the job done, and you certainly don't need to be intimidated about it or feel obligated to learn it right off. Even Haskell isn't actually so difficult to grasp the basics of, if you keep this in mind and just think "Do IO in a 'do' block" and go about your way. See [1]. You don't have to know everything in any language just to get some work done, a lot of times advanced features are just that: advanced, stuff for doing things a bit more efficiently, or to handle certain rough edge cases. Learn them in their own time, and they'll make you better at what you do, but don't get wrapped up too much in expecting perfect efficiency from yourself. A lot of programmers seem to be, as a people, kinda bad at this kind of self-reflection, like we're all sheep in wolves' clothing trying to avoid showing a hint of weakness. I know I sure am. There's nothing wrong with not knowing something, just try and take a moment learn it when you can. [1] http://blog.jle.im/entry/io-monad-considered-harmful http://blog.jle.im/entry/io-monad-considered-harmful

enoch_r 11y ago

If you have an understanding of functions like map, filter, and reduce, transducers are actually pretty easy. Say you have `(map inc [1 2])`. You can run that, and get `'(2 3)`. A transducer is the `(map inc)` part of that call (slightly confusingly, this isn't partial application or currying). You can apply it to something like `[1 2]`, but you can also compose with it, by combining it with say, `(filter even?)` to get something that represents the process of incrementing everything, then removing odd numbers. Or you can put in things that aren't collections, like asynchronous channels, and get back a new channel with the values modified accordingly. That's pretty much it. What I think I love most about Clojure is that there are fantastic, esoteric, academic ideas that, when I read about them in a context like this for the first time, I a) do not understand them, and b) have no idea how they would be useful. Then I read an example or two, and suddenly it's apparent that the tool is really as simple as it can be--there's very little accidental complexity--and is extremely useful.

deleted 11y ago
[deleted]
aoeuasdf1 11y ago
The way you explain it, it's no different from functions and function composition; in which case, why invent new vocabulary? I do remember looking into them before and translating them into Haskell and they ended up not being identical to functions in the trivial sense that you suggest, but I forget how.
- arohner 11y ago
  Why have new vocabulary for the state monad? Transducers are mostly function and function composition, but with a specific signature. There are a handful of contracts on a transducer, so it is useful to have a name, so you can say "this function takes a transducer" and "this function returns a transducer".
- kazinator 11y ago
  Transducers are functions. The thing is that they are functions that are designed to serve as the functional argument to reduce. And they pair with ordinary functions which are not transducers. For instance if we have (map inc [1 2]), there exists a transducer function T such that: (reduce T [1 2]) == (map inc [1 2]) I.e. we can somehow do "map inc" using reduce. Okay? Now, the clever thing is this: why don't we allow map to be called without the list argument? Just let it be called like this: (map inc) This looks like partial application, right? Now what would partial application do? It would curry the "inc", returning a function of one argument that takes a list, i.e.: ;; if it were partial application, then: ((map inc) [1 2]) ;; same as (map inc [1 2]) But Hickey did something clever; he overloaded functions like map so that (map inc) returns T! (reduce (map inc) [1 2]) ;; same as (map inc [1 2]) The cool thing is that this (map inc) composes with other functions of its kind. So you can compose together the transducers of list processing operations, which are then put into effect inside a single reduce, and the behavior is like the composition of the original list processors. It's like a linear operator; like LaPlace. Composition of entire list operations in the regular domain corresponds to composition of operations on individual elements in the "t-domain".

brudgers 11y ago

Clojure is sophisticated [0] but it is hard boiled down to necessary complexity. This means that ordinary language features like interop [1] are well sugared and more abstract concepts like transducers are simple to implement and map well to their description [2]. Stuart Halloway's Programming Clojure captures this idea. [0] and big for practical purposes like Common Lisp. [1] you can get at all of Java perhaps better than you can from Java using the REPL. [2] like lexical scope and continuations in Scheme.

spion 11y ago

Transducers create functions that are meant to be passed to reduce (i.e. take accumulator and element and return a new accumulator). Its possible to implement most other functions (map, filter, take etc.) using reduce. Transducers take advantage of that. Unfortunately, if you try to do that, you'll notice that the implementation is sometimes tied with the way you build the entity: e.g. for vectors, map implemented in terms of reduce would start with an empty vector then append to it. That sucks. We want operation chains that are independent of the data structure they operate on. We want them to work on vectors, lists, channels, whatever - anything that can have a reduce-like operation (anything reducible) However, it turns out you don't necessarily have to recreate the entity (e.g. list) when chaining. All you need to know how to do is invoke the next operation in the chain, i.e. the next reduction function. For example: * map can apply the function on the element to get a new result, then call the next reduction function with the accumulator and that new result. * filter can check the element and either return the old accumulator or apply the next reduction function with the element, etc. Therefore, transducers simply take an additional argument: the next reduction function that should be applied. This lets you build up a chain of operations (e.g. map filter etc) that doesn't care about the kind of entity they're operating on. Only the last "step" must be a reduction function that needs to know how to build the result.

phren0logy 11y ago

You may feel less intimidated by "Clojure for the Brave and True." The landing page features a rodent with an eye patch and a sword. http://www.braveclojure.com/ http://www.braveclojure.com/

jsilence 11y ago
> Delete ~/.emacs or ~/.emacs.d if they exist Ehhhh, no!
- KurtMueller 11y ago
  Hence the emphasis on Clojure for the Brave.
- ZainRiz 11y ago
  Don't get disheartened. I just started this tutorial last weekend (and had no emacs experience before) and it's been great!

yogthos 11y ago

Clojure is one of the easiest languages to learn. You need to know very few concepts to become productive in it. I get co-op students very 4 months at work and they generally start doing useful stuff within a week or so. I wrote a conceptual starter guide a little while back ( https://yogthos.github.io/ClojureDistilled.html https://yogthos.github.io/ClojureDistilled.html ), that covers all the basics that you need to know to get up and running.

jgalt212 11y ago

Are transducers necessary in Clojure because functions of function of functions (etc...) on immutable data structures execute slowly?

harlanji 11y ago
They help relieve pressure on the garbage collector by eliminating intermediate sequence allocations (eg. (comp (map a) (map b) (filter c) (map d)) would create 4 sequences, transducers create none). Consequently you can work with results incrementally unless there is an intermediate flush required such as for a windowed aggregation. I imagine most applications aren't very sensitive to the performance gain, but it's good to know for when you need it. In addition it's a nice and testable, compos-able pattern. I've only done backend work, no cljs yet, but I'd call it reasonable practice to think in terms of compositions/transducers for most data transformation pipelines in the future though, throughout the stack, whether performance matters or not.

tsmarsh 11y ago

Its more like 18 months. Unless you already know a lisp or Haskell. The only thing I can say is that it is totally worth it, I know very few people who regret putting it in their head. The same is less true for Ruby, php, Visual Basic.

nbardy 11y ago

I had a similar feeling when I first starting using Clojure, but I found it was more of a discomfort from discussing programming language with a direct and accurate vocabulary. After a while I've become much more comfortable reading about and watching videos on programming languages in this style and I really enjoy being able to discuss and think about design decisions in a straightforward way.

goldfeld 11y ago

Dive in! It's like beginning ballet over twenty: you'd really have to trust your slow, consistent, building momentum to eventually get you there. Learning Clojure up to getting remotely competent with it did take me a year and a half, during which I used it in all my projects. Also including getting into Emacs. I breathed it all throughout. Now I'm good in it, I have ease designing big FP systems, and I finally decided to learn transducers a few weeks ago and it took me me just an hour to grasp/implement it in my app. Neither a decade :)

jwhitlark 11y ago

Basic competence comes pretty quick, it's a small core language, compared to most. Most things like transducers you can ignore for a long time. The longest part of learning it for me was learning to think functionally, but you can do that in pieces, and nearly all of what you learn is applicable to any functional language, or even imperative languages with functional aspects.