Re: noob questions - Hello world + learning
New to Clojure (find it fascinating so far, in large part due to watching approximately a billion Rich Hickey vids on YouTube). I had a similar question and figured I just resurrect this thread on it. My naive thought was that when you (re)def a variable, you aren't actually copying over the old memory location, but instead simply re-creating a pointer to a new value or place in memory. To take this example further, I'm wondering what goes on under the hood when I use replace like this: (def my-vec [1 2 3 4 5]) = (var user/my-vec) (def my-vec (assoc my-vec 2 hello)) = (var user/my-vec) my-vec = [1 2 hello 4 5] Is there a good explanation out there of what happens to the old my-vec and whether the new my-vec actually overwrites it, points to it, or points to a completely new location in memory? Another way to phrase this question: is this real mutability or just the appearance of mutability? On Tuesday, June 15, 2010 4:51:00 AM UTC-7, Joost wrote: On Jun 14, 10:09 pm, Jared tri...@gmail.com wrote: Also, I thought this language is functional but I'm able to do change declarations in the repl. For example: user= (def x 1) #'user/x user= x 1 user= (def x 2) #'user/x user= x 2 user= (def x (+ 1 x)) #'user/x user= x 3 Why does that happen? This seems to go against the ideas of functional programming. I can do the same things with functions too. It's true that def isn't a strictly functional construct. That's by design, since def is the construct that allows you to define and set globally accessible vars, which includes all globally accessible functions. If you couldn't re-def a var, you couldn't redefine functions while coding (or modify/extent existing functions using macros etc). Clojure (like most Lisps) is a dynamic language with strong support for interactive development - and you need redefineable vars (or something similar) for that. The alternative is to recompile/load the whole program every time you change a function definition. And that sucks too much. In idiomatic code, you only use (def) and its variants to set up globally reachable data/functions across all threads and you don't, for example, use def as a way to get variable variables - you will get bitten if you try. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: noob questions - Hello world + learning
In your example, [1 2 3 4 5] allocates and initializes a vector with the 5 elements 1 2 3 4 5. The first (def my-vec ...) also allocates a Var, and makes it 'point' at the vector [1 2 3 4 5]. When you do (assoc my-vec 2 hello), it looks up the current value pointed at by my-vec, which is the immutable vector [1 2 3 4 5], and it creates a new vector [1 2 hello 4 5]. That new vector is also immutable. In the common case, it does not copy the entire vector [1 2 3 4 5] and then modify the element 3 to hello -- it uses a technique called 'path copying' to leave most of the memory that has been allocated shared between the two vectors [1 2 3 4 5] and [1 2 hello 4 5]. The second (def my-vec ...) does mutate the 'pointer' for my-vec so that it no longer points at [1 2 3 4 5], but instead points at [1 2 hello 4 5]. This is true mutation, not of the vectors, but of the Var my-vec. Such mutation helps support redefinition of functions during interactive REPL sessions, among other things. Andy On Thu, Jul 3, 2014 at 2:39 PM, Evan Zamir zamir.e...@gmail.com wrote: New to Clojure (find it fascinating so far, in large part due to watching approximately a billion Rich Hickey vids on YouTube). I had a similar question and figured I just resurrect this thread on it. My naive thought was that when you (re)def a variable, you aren't actually copying over the old memory location, but instead simply re-creating a pointer to a new value or place in memory. To take this example further, I'm wondering what goes on under the hood when I use replace like this: (def my-vec [1 2 3 4 5]) = (var user/my-vec) (def my-vec (assoc my-vec 2 hello)) = (var user/my-vec) my-vec = [1 2 hello 4 5] Is there a good explanation out there of what happens to the old my-vec and whether the new my-vec actually overwrites it, points to it, or points to a completely new location in memory? Another way to phrase this question: is this real mutability or just the appearance of mutability? On Tuesday, June 15, 2010 4:51:00 AM UTC-7, Joost wrote: On Jun 14, 10:09 pm, Jared tri...@gmail.com wrote: Also, I thought this language is functional but I'm able to do change declarations in the repl. For example: user= (def x 1) #'user/x user= x 1 user= (def x 2) #'user/x user= x 2 user= (def x (+ 1 x)) #'user/x user= x 3 Why does that happen? This seems to go against the ideas of functional programming. I can do the same things with functions too. It's true that def isn't a strictly functional construct. That's by design, since def is the construct that allows you to define and set globally accessible vars, which includes all globally accessible functions. If you couldn't re-def a var, you couldn't redefine functions while coding (or modify/extent existing functions using macros etc). Clojure (like most Lisps) is a dynamic language with strong support for interactive development - and you need redefineable vars (or something similar) for that. The alternative is to recompile/load the whole program every time you change a function definition. And that sucks too much. In idiomatic code, you only use (def) and its variants to set up globally reachable data/functions across all threads and you don't, for example, use def as a way to get variable variables - you will get bitten if you try. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: noob questions - Hello world + learning
I want to thank everyone for the helpful comments, and no worries about the typing nickikt. I'll check out SICP. I've been playing around in the repl, getting used to prefix notation, and I found out the doc command. It makes learning this stuff much faster. I guess I should have been more clear about my level of CS/ programming knowledge. I took the CS-AP AB exam about 4 years ago, so I know a little, and am slowly remembering a little more. The most complex program I've written was a python program that set up the initial game state for the board game Settlers of Catan. So I have a small amount of familiarity with data structures, big O notation and writing a few scripts. I'm trying to grok this hello world template before I move on to other stuff. What is the ns line for? I read the documentation on ns, but it didn't make much sense to me. Is ns related to scope? All I know is when I delete the ns line the program doesn't compile. Why is it that function declarations must have the arguments as vector(s), and not lists? As in, why can't I declare a function like this? (defn my-test (list n) (+ n 1)) In that default template, why does that hello world program even run? At what line is main called? By the way, thank you nickikt for the explanation that main is an overloaded function. That was not obvious to me. Also, I thought this language is functional but I'm able to do change declarations in the repl. For example: user= (def x 1) #'user/x user= x 1 user= (def x 2) #'user/x user= x 2 user= (def x (+ 1 x)) #'user/x user= x 3 Why does that happen? This seems to go against the ideas of functional programming. I can do the same things with functions too. Also, is it preferred to put all this miscellaneous questions I come up with in this thread, or to make a new topic for each question? -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: noob questions - Hello world + learning
On Jun 14, 10:09 pm, Jared tri...@gmail.com wrote: Also, I thought this language is functional but I'm able to do change declarations in the repl. For example: user= (def x 1) #'user/x user= x 1 user= (def x 2) #'user/x user= x 2 user= (def x (+ 1 x)) #'user/x user= x 3 Why does that happen? This seems to go against the ideas of functional programming. I can do the same things with functions too. It's true that def isn't a strictly functional construct. That's by design, since def is the construct that allows you to define and set globally accessible vars, which includes all globally accessible functions. If you couldn't re-def a var, you couldn't redefine functions while coding (or modify/extent existing functions using macros etc). Clojure (like most Lisps) is a dynamic language with strong support for interactive development - and you need redefineable vars (or something similar) for that. The alternative is to recompile/load the whole program every time you change a function definition. And that sucks too much. In idiomatic code, you only use (def) and its variants to set up globally reachable data/functions across all threads and you don't, for example, use def as a way to get variable variables - you will get bitten if you try. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: noob questions - Hello world + learning
On Mon, Jun 14, 2010 at 4:09 PM, Jared tri...@gmail.com wrote: I'm trying to grok this hello world template before I move on to other stuff. What is the ns line for? I read the documentation on ns, but it didn't make much sense to me. Is ns related to scope? All I know is when I delete the ns line the program doesn't compile. It's might not be that constructive to grok the hello world template before moving on. That template is largely about creating a Java executable. ns creates a namespace. It allows your program to modular and prevents the likelihood of name clashes. my-namespace/foo your-namespace/foo This way to two functions can have the same name yet be used together in the same program. Why is it that function declarations must have the arguments as vector(s), and not lists? As in, why can't I declare a function like this? (defn my-test (list n) (+ n 1)) This is a Clojure syntax thing. Bindings happen inside of vectors. In that default template, why does that hello world program even run? At what line is main called? By the way, thank you nickikt for the explanation that main is an overloaded function. That was not obvious to me. ns declaration here is being used to generate a Java class from this namespace. The class that defines main in a Java program is the entry point. Also, I thought this language is functional but I'm able to do change declarations in the repl. For example: user= (def x 1) #'user/x user= x 1 user= (def x 2) #'user/x user= x 2 user= (def x (+ 1 x)) #'user/x user= x 3 This is definitely one way to introduce mutability into your program but this is considered bad form. David -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: noob questions - Hello world + learning
Hi Jared, Some good clojure specific learning resources; http://java.ociweb.com/mark/clojure/article.html and the essential http://clojure.org/ - Regards, Adrian -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: noob questions - Hello world + learning
Hello, I have a some comments (on comments and more :)) First this (comment . ) There are diffrent kind ofs comments. If you just want to note something you can do ; but mabey you want to have a example how to use something in your Code then use (comment ). With defn you creat a new function with a name. First switch the order of your function implementation (defn -main ([] (-main world)) ([greetee] (println (str Hello greetee ! What you are doing is implementing the -main method twise one for no arguments once for one argument ([] and [greetee]) This is a handy because you can make an easy and fast default implementation. An other way would be doing it like this (defn -main ([] (println Hello world)) ([greetee] (println (str Hello greetee ! But if you want to change something (Hello to helo or something) you would have to do this two times. So you just call your second implementation ([greetee] .. ) with world. So a change got something in ([greetee] ) works for both implementations. So what does (str Hello greetee) do? Lets say you call -main like this (-main nickik) then the greetee variable is a string. With (str ...) you make one string out of the arguments. (str Hallo nickik) -- Hallo nickik than that is printed. If you call -main like this (-main 75) is will work because 75 will be converted to 75. Because you new some additional information. In most langauges you would have to tell the compiler what greetee is ( int or string ) these are what we call static languages but in clojure you dont have to. That is wath makes a language dynamic. So you can pass in everything that can be converted to a string. Interessting that you learn programming with clojure. I had to unlearn so many bad stuff that I was used to. If you want to use a lot of clojure you should learn git a liddle bit (there is a free book Pro Git) most of clojure stuff people do is on github.org You can try the laprepl http://github.com/relevance/labrepl its made to help getting started Some links for you to finish this up some are probebly hard for you: http://clojure.blip.tv/ -- videos about clojure (most of them from rich himself if you are hot for more surf infoq.com) The book that David Nolen mentiond: http://mitpress.mit.edu/sicp/full-text/book/book.html and Videos to help you learn you can found here: From MIT 1986: http://www.youtube.com/watch?v=2Op3QLzMgSY and the next 20 vids but you can download them too just google them. Or if you like Berkeley more http://www.youtube.com/watch?v=zmYqShvVDh4 More on Programming in (its in java but it starts at lvl absolute ZERO) http://www.youtube.com/user/stanforduniversity?blend=2ob=4#g/c/84A56BC7F4A1F852 But i recommend stike with the SICP book and courses they are harder but its worth it. Specaly if you like clojure. Sorry for tipping errors Great On Jun 11, 5:47 pm, Jared tri...@gmail.com wrote: Hi everyone, I'm 100% new to LISP, 95% new to Java, and 90% new to programming in general. Where and how would you recommend learning Clojure? I'm planning on buying Programming Clojure, but until then what would you suggest? I got Netbeans working with Clojure and the default template is this: (comment Sample clojure source file ) (ns com.yourcompany.defpackage (:gen-class)) (defn -main ([greetee] (println (str Hello greetee !))) ([] (-main world))) It ran and printed Hello world!. Can anyone explain to me in detail what each statement means. I'm particularly confused by: (comment Sample clojure source file ) I thought all comments began with ; ? I understand what println does and that's it. Thanks in advance everyone. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: noob questions - Hello world + learning
If your are new to programming I recommend reading at least the first three chapters of The Structure and Interpretation of Computer Programs. It's available online. David On Friday, June 11, 2010, Jared tri...@gmail.com wrote: Hi everyone, I'm 100% new to LISP, 95% new to Java, and 90% new to programming in general. Where and how would you recommend learning Clojure? I'm planning on buying Programming Clojure, but until then what would you suggest? I got Netbeans working with Clojure and the default template is this: (comment Sample clojure source file ) (ns com.yourcompany.defpackage (:gen-class)) (defn -main ([greetee] (println (str Hello greetee !))) ([] (-main world))) It ran and printed Hello world!. Can anyone explain to me in detail what each statement means. I'm particularly confused by: (comment Sample clojure source file ) I thought all comments began with ; ? I understand what println does and that's it. Thanks in advance everyone. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: noob questions - Hello world + learning
I don't think that Structure and Interpretion of Computer Programs is a good first-book if you want to start lisp-programming (Especially Clojure). It's very detailed and gives much insights, but Clojure is way more practical than this book. If you want to start programming Clojure, I'd recommend Pragmatic Programming Clojure or The Joy of Clojure (Even when JoC isn't finished yet). To your original question: That's a hard piece of code to start with. I'd recommend firing up a repl and trying with this instead of this template you've mentioned. On Sun, Jun 13, 2010 at 6:25 PM, David Nolen dnolen.li...@gmail.com wrote: If your are new to programming I recommend reading at least the first three chapters of The Structure and Interpretation of Computer Programs. It's available online. David On Friday, June 11, 2010, Jared tri...@gmail.com wrote: Hi everyone, I'm 100% new to LISP, 95% new to Java, and 90% new to programming in general. Where and how would you recommend learning Clojure? I'm planning on buying Programming Clojure, but until then what would you suggest? I got Netbeans working with Clojure and the default template is this: (comment Sample clojure source file ) (ns com.yourcompany.defpackage (:gen-class)) (defn -main ([greetee] (println (str Hello greetee !))) ([] (-main world))) It ran and printed Hello world!. Can anyone explain to me in detail what each statement means. I'm particularly confused by: (comment Sample clojure source file ) I thought all comments began with ; ? I understand what println does and that's it. Thanks in advance everyone. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- Moritz Ulrich Programmer, Student, Almost normal Guy http://www.google.com/profiles/ulrich.moritz -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
