6 ms·

Today you have 3 main alternatives: * Common Lisp (used by the author of the article) * Scheme * Clojure

by octopus 14y ago

sillysaurus 14y ago
One thing that intrigues me about clojure is that it affords some unique benefits, by virtue of being a lisp. For fun I want to try to write a clojure program which generates C code for a tiny game engine. e.g. you run the program, and it spits out .c and .h files which you can then compile and run. Then, the challenge is to make it generate java code, too. I.e. in addition to the C code, which you can build and run, it also generates that same functionality in Java code, which you can run on JRE. So the game engine itself would be specified in clojure, and yet it would be "automatically implemented" across two very-different platforms! It's a fun challenge, I think. Maybe not doable, or doable only in a horrible way, but still fun. But the point is this: that's a great example of a problem which would be pretty much impossible in a non-lisp language. In order to achieve that in Python, you'd probably be forced to implement a lightweight lisp within Python. So that may demonstrate an answer to the question, "Why Lisp?" ... certain problems can be solved only in lisp, or by reimplementing the list-processing concepts of lisp.
- octopus 14y ago
  There is already a project that translates ClojureScript to Scheme https://github.com/takeoutweight/clojure-scheme https://github.com/takeoutweight/clojure-scheme from which you can generate C code. Theoretically you could use the generated C code on any OS with a standard C compiler.
- airfoil 14y ago
  Why generate Java code if Clojure runs on the JVM? Why is it "pretty much impossible" generate the game engine C code in a non-lisp language? What is it about Lisp that makes it possible?
  - sillysaurus 14y ago
    The motivation behind "generating Java" was that the game could then be deployed in a browser, just like Minecraft is. Maybe Clojure can already do that though. I haven't looked yet. =) Clojure runs on the JVM, but perhaps Clojure is expensive in the context of a 60-frame-per-second realtime app. I doubt it would be significantly more expensive than Java, but that's something to test. So by generating Java, then it would be an interesting system because it winds up producing the same sort of code which Notch made by hand to deploy Minecraft to a browser. Yet it's derived "from the clojure code". And yet it's also generating C code, which is also derived "from the clojure code". So it's very meta, which I can't resist exploring. Why is it "pretty much impossible" generate the game engine C code in a non-lisp language? Well, it's straightforward for you write a program which generates some C code. But how about "either C, or Java"? Or "either C, or Java, or Haskell", ... etc. You'll soon discover that the nature of the implementation is completely different for different languages. A Haskell game engine would look utterly nothing like a C implementation would look. So the situation is, you would need an intermediate source code representation of your game engine which supports introspection. And whatever data structure you use must also be able to be modified during the "code generation", because it's not until the codegen step that you know what sort of special-casing you'll have to do (in order to generate code which implements your game engine in e.g. haskell, or brainfuck, or... etc. Point being: each of those has a different set of special-case requirements, and you can't know which until you're already in the codegen phase.) So, you could use a different language, and you could represent your "game engine source code" as, say, JSON. And you could have conventions for what your various operations "within that JSON string" actually mean -- e.g. whether you use infix notation, or prefix notation, or.. etc. And then you could have a notation for how to specify a function, within that JSON string. And so on. But then, at the end of it all, you wind up with a poorly implemented version of what lisp already offers you. It lets you do all of that automatically, because those features are built right in to the language. Indeed, the language is the primary reason the features are possible: Everything is a list, and everything has access to all lists at all phases of the program's lifespan. You can run at compile time, or compile at run time, etc. You have access to the entire syntax tree at all times, in every program you write, which enables you to manipulate it. You simply can't do that with e.g. Python. Hence the requirement for an "intermediate thing, which you can manipulate" -- we happened to decide on using JSON as the representation, but you could've easily decided to use something else, etc. The point is, that "intermediate representation" is just a poorly-reimplemented version of the toolset which Lisp gives you by default.
strobe 14y ago
And, It's really hard to choose one! All of 3 dialects has own unique benefits and lacks.
- z92 14y ago
  What does Clojure lacks in the language?
  - chimeracoder 14y ago
    Clojure adds syntax, which breaks some of the inherent symmetry of Lisp slightly[0]. This isn't something you're likely to notice unless you do a lot of heavy metaprogramming. Clojure cannot guarantee elimination of tail calls, because of the limitations of the underlying JVM. This also means that it can't properly handle corecursion in the same way that pretty much every single other Lisp can. (Both of these have been discussed before many times before on HN, so I can pre-empt the next comment in this thread, which will be someone pointing out that Clojure provides "loop" and the "recur" macro - to which I'd respond, yes, they're logically equivalent in the end, but having to force the transformation to a loop explicitly breaks the paradigm, which for me is the whole point of using a Lisp. This is one of those topics that can be discussed ad nauseum with no "conclusion", so it's not worth spending too much time on it.) Lastly, anytime you're dealing with binary compatibility between various JVM languages, the abstraction is inherently a bit leaky. I haven't used Clojure myself, so I can't comment specifically there, but from my experience with using Java libraries in Scala, I can testify that some of the warts of Java end up leaking into Scala code. Nothing debilitating, just a bit frustrating[1]. [0] Racket does too, but the "syntax" added (square brackets) has the same semantics, so it's really just an equivalent token - an alias, if you will. [1] One particular example I remember has to do with how Foo.class in Java works, and how a library dependent on this particular pattern has to be used in Scala - it just gets a bit messy.
    - peatmoss 14y ago
      I wonder if, in the future, this limitation of Clojure will go away. I know there has been talk of the JVM folk adding things like support for tail recursion. That said, I'm not smart enough to know whether talking about adding support for tail recursion translates to "Once we're agreed, let us go ahead and solve this tractable problem," or if it translates to "Gee this would be nice, but it's wicked hard."
qznc 14y ago
Scheme is not a single alternative. Racket [0] is a Scheme, which can be compared to things like Python or Ruby. There are other implementations, which should be used for different uses. For example, Chibi Scheme [1] is a nice alternative to Lua, but not to Python or Ruby. Given your other two Lisps, I rather make this list: * Common Lisp (which implementation?) * Racket * Clojure [0] http://racket-lang.org/ http://racket-lang.org/ [1] http://synthcode.com/wiki/chibi-scheme http://synthcode.com/wiki/chibi-scheme
- gnosis 14y ago
  I think Chicken[1] is a very attractive Scheme alternative. It's full-featured, fast, compiles down to C, has a very nice library (egg) system, and a relatively large and active user community (as far as Schemes go). [1] - http://call-cc.org/ http://call-cc.org/
  - klutometis 14y ago
    Hear, hear; I've been using Chicken for commercial and personal projects for about five years now. It keeps getting better. Occasionally, Racket has a package that I'd like to port (e.g. datalog); but I find it otherwise overbearing. Chicken has found some local maximum of efficiency and availability of useful libraries.
- pmelendez 14y ago
  I would add Tiny Scheme as an embedding scripting language or as base of a DSL

Today you have 3 main alternatives: * Common Lisp (used by the author of the article) * Scheme * Clojure

by octopus 14y ago

Today you have 3 main alternatives: * Common Lisp (used by the author of the article) * Scheme * Clojure

One thing that intrigues me about clojure is that it affords some unique benefits, by virtue of being a lisp. For fun I want to try to write a clojure program which generates C code for a tiny game engine. e.g. you run the program, and it spits out .c and .h files which you can then compile and run. Then, the challenge is to make it generate java code, too. I.e. in addition to the C code, which you can build and run, it also generates that same functionality in Java code, which you can run on JRE. So the game engine itself would be specified in clojure, and yet it would be "automatically implemented" across two very-different platforms! It's a fun challenge, I think. Maybe not doable, or doable only in a horrible way, but still fun. But the point is this: that's a great example of a problem which would be pretty much impossible in a non-lisp language. In order to achieve that in Python, you'd probably be forced to implement a lightweight lisp within Python. So that may demonstrate an answer to the question, "Why Lisp?" ... certain problems can be solved only in lisp, or by reimplementing the list-processing concepts of lisp.

octopus 14y ago
There is already a project that translates ClojureScript to Scheme https://github.com/takeoutweight/clojure-scheme https://github.com/takeoutweight/clojure-scheme from which you can generate C code. Theoretically you could use the generated C code on any OS with a standard C compiler.
airfoil 14y ago
Why generate Java code if Clojure runs on the JVM? Why is it "pretty much impossible" generate the game engine C code in a non-lisp language? What is it about Lisp that makes it possible?
- sillysaurus 14y ago
  The motivation behind "generating Java" was that the game could then be deployed in a browser, just like Minecraft is. Maybe Clojure can already do that though. I haven't looked yet. =) Clojure runs on the JVM, but perhaps Clojure is expensive in the context of a 60-frame-per-second realtime app. I doubt it would be significantly more expensive than Java, but that's something to test. So by generating Java, then it would be an interesting system because it winds up producing the same sort of code which Notch made by hand to deploy Minecraft to a browser. Yet it's derived "from the clojure code". And yet it's also generating C code, which is also derived "from the clojure code". So it's very meta, which I can't resist exploring. Why is it "pretty much impossible" generate the game engine C code in a non-lisp language? Well, it's straightforward for you write a program which generates some C code. But how about "either C, or Java"? Or "either C, or Java, or Haskell", ... etc. You'll soon discover that the nature of the implementation is completely different for different languages. A Haskell game engine would look utterly nothing like a C implementation would look. So the situation is, you would need an intermediate source code representation of your game engine which supports introspection. And whatever data structure you use must also be able to be modified during the "code generation", because it's not until the codegen step that you know what sort of special-casing you'll have to do (in order to generate code which implements your game engine in e.g. haskell, or brainfuck, or... etc. Point being: each of those has a different set of special-case requirements, and you can't know which until you're already in the codegen phase.) So, you could use a different language, and you could represent your "game engine source code" as, say, JSON. And you could have conventions for what your various operations "within that JSON string" actually mean -- e.g. whether you use infix notation, or prefix notation, or.. etc. And then you could have a notation for how to specify a function, within that JSON string. And so on. But then, at the end of it all, you wind up with a poorly implemented version of what lisp already offers you. It lets you do all of that automatically, because those features are built right in to the language. Indeed, the language is the primary reason the features are possible: Everything is a list, and everything has access to all lists at all phases of the program's lifespan. You can run at compile time, or compile at run time, etc. You have access to the entire syntax tree at all times, in every program you write, which enables you to manipulate it. You simply can't do that with e.g. Python. Hence the requirement for an "intermediate thing, which you can manipulate" -- we happened to decide on using JSON as the representation, but you could've easily decided to use something else, etc. The point is, that "intermediate representation" is just a poorly-reimplemented version of the toolset which Lisp gives you by default.

strobe 14y ago

And, It's really hard to choose one! All of 3 dialects has own unique benefits and lacks.

z92 14y ago
What does Clojure lacks in the language?
- chimeracoder 14y ago
  Clojure adds syntax, which breaks some of the inherent symmetry of Lisp slightly[0]. This isn't something you're likely to notice unless you do a lot of heavy metaprogramming. Clojure cannot guarantee elimination of tail calls, because of the limitations of the underlying JVM. This also means that it can't properly handle corecursion in the same way that pretty much every single other Lisp can. (Both of these have been discussed before many times before on HN, so I can pre-empt the next comment in this thread, which will be someone pointing out that Clojure provides "loop" and the "recur" macro - to which I'd respond, yes, they're logically equivalent in the end, but having to force the transformation to a loop explicitly breaks the paradigm, which for me is the whole point of using a Lisp. This is one of those topics that can be discussed ad nauseum with no "conclusion", so it's not worth spending too much time on it.) Lastly, anytime you're dealing with binary compatibility between various JVM languages, the abstraction is inherently a bit leaky. I haven't used Clojure myself, so I can't comment specifically there, but from my experience with using Java libraries in Scala, I can testify that some of the warts of Java end up leaking into Scala code. Nothing debilitating, just a bit frustrating[1]. [0] Racket does too, but the "syntax" added (square brackets) has the same semantics, so it's really just an equivalent token - an alias, if you will. [1] One particular example I remember has to do with how Foo.class in Java works, and how a library dependent on this particular pattern has to be used in Scala - it just gets a bit messy.
  - peatmoss 14y ago
    I wonder if, in the future, this limitation of Clojure will go away. I know there has been talk of the JVM folk adding things like support for tail recursion. That said, I'm not smart enough to know whether talking about adding support for tail recursion translates to "Once we're agreed, let us go ahead and solve this tractable problem," or if it translates to "Gee this would be nice, but it's wicked hard."

qznc 14y ago

Scheme is not a single alternative. Racket [0] is a Scheme, which can be compared to things like Python or Ruby. There are other implementations, which should be used for different uses. For example, Chibi Scheme [1] is a nice alternative to Lua, but not to Python or Ruby. Given your other two Lisps, I rather make this list: * Common Lisp (which implementation?) * Racket * Clojure [0] http://racket-lang.org/ http://racket-lang.org/ [1] http://synthcode.com/wiki/chibi-scheme http://synthcode.com/wiki/chibi-scheme

gnosis 14y ago
I think Chicken[1] is a very attractive Scheme alternative. It's full-featured, fast, compiles down to C, has a very nice library (egg) system, and a relatively large and active user community (as far as Schemes go). [1] - http://call-cc.org/ http://call-cc.org/
- klutometis 14y ago
  Hear, hear; I've been using Chicken for commercial and personal projects for about five years now. It keeps getting better. Occasionally, Racket has a package that I'd like to port (e.g. datalog); but I find it otherwise overbearing. Chicken has found some local maximum of efficiency and availability of useful libraries.
pmelendez 14y ago
I would add Tiny Scheme as an embedding scripting language or as base of a DSL