What are the basic structural aspects that should exist in Julia code I am writing? I will link some other languages' implementation of this for reference.
I am looking for officially sanctioned components for the language itself, not one's opinion on best practices.
Basic structure of a C program
Basic structure of a Java program
First off, if you are new to Julia and the structure of writing a program therein, I suggest you check out the Official Julia Docs for a great explanation as to how to get started writing code in Julia.
If you are coming from a language like Java and read the documentation linked above, you may be a little confused as to where the docs on the structure of a Julia program are. To my understanding, that doc does not exist for a few reasons.
Julia as a language imposes very little on you as the programmer. This can lead to a bit of uncertainty and doubt with all of the newfound freedom. There are some basic structures that should be followed, despite the flexibility the language provides:
using and import statements are generally made at the very top of the file.
That's about it! (Feel free to edit if you think there's more).
It's also worth checking out the Julia Style Guide for things like:
Write functions, not just scripts:
Writing code as a series of steps at the top level is a quick way to get started solving a problem, but you should try to divide a program into functions as soon as possible. Functions are more reusable and testable, and clarify what steps are being done and what their inputs and outputs are. Furthermore, code inside functions tends to run much faster than the top-level code, due to how Julia's compiler works.
In general, Julia is flexible. There are very few things that you have to include in your program.
It's important to designate the difference between writing a simple Julia script and creating a project in Julia.
While there are limited structural suggestions for creating a simple script, there are a number of suggestions related to how one can structure a Julia Project. In fact, many of these aspects are built into Julia itself! You can find out more about creating Julia Projects (which should have a similar if not the same structure as Julia packages) here.
Note: If you are trying to find the structure of a Package in Julia, a great resource would be PackageTemplate.jl.
Larger Julia programs tend to first have modules that are included, then any const declaration of const global variables, then one or more functions, then a statement that calls the first function run.
However, your question may be due to the fact that you already know that C and Java have a certain structure mandated in order to compile and run.
Perhaps comparing a "Hello, World!" minimal programs would help.
Here is a Julia minimal program:
println("Hello, World!")
Julia its inherits its free program structuring more from Fortran and especially Python than C or Java. Here is a Python minimal program:
print("Hello, World!")
Here is a Fortran77 minimal program:
print *, "Hello, World!"
On the other hand, C requires, for the same function, a main() wrapper function and inclusion of code for printing to screen. Here is a C minimal program:
#include <stdio.h>
int main()
{
return printf("Hello, World!\n");
}
Java also requires that its main() function be wrapped within a user defined class. Here is a Java minimal program:
public class HelloWorld
{
public static void main(String[] args)
{
System.out.println("Hello, World!");
}
}
So, Julia simply does not have certain structural requirements that you find well documented for the C or Java languages.
Related
What does Qt Quick Compiler do exactly? My understanding was that it "compiles" QML/JS into C++ and integrates this into the final binary/executable. So, there is no JIT compilation or any other JS-related things during runtime.
However, I saw somewhere an article that claimed that it's not like this and actually it only "bundles" QML/JS into final binary/executable, but there is still some QML/JS-related overhead during runtime.
At the documentation page there is this explanation:
.qml files as well as accompanying .js files can be translated into
intermediate C++ source code. After compilation with a traditional
compiler, the code is linked into the application binary.
What is this "intermediate C++ source code"? Why not just "C++ source code"? That confuses me, but the last statement kinda promises that yes, it is a C++ code, and after compiling it with C++ compiler you will have a binary/executable without any additional compiling/interpretation during runtime.
Is it how it actually is?
The code is of an intermediate nature because it doesn't map Javascript directly to C++. E.g. var i = 1, j = 2, k = i+j is not translated to the C++ equivalent double i = 1., j = 2., k = i+j. Instead, the code is translated to a series of operations that directly manipulate the state of the JS virtual machine. JS semantics are not something you can get for free from C++: there will be runtime costs no matter how you implement it. There is no additional compiling nor interpretation, but the virtual machine that implements the JS state still has to exist.
That's not an overhead easy to get rid of without emitting a lot mostly dead code to cover all contexts in which a given piece of code might run, or doing just-in-time compilation that you wanted to avoid. That's the primary problem with JavaScript: its semantics are such that it's generally not possible to translate it to typical imperative statically typed code that gives rise to "standard" machine code.
Your question already contains the answer.
It compiles the code into C++, that is of intermediate nature as it is not enough to have C++-Code. You need binaries. So after the compilation to C++, the files are then compiled into binaries. Those are then linked.
The statement only says: We do not compile to binary, but to C++ instead. You need to compile it into a binary with your a C++-Compiler of your choice.
The bundeling happens, if you only put it into the resources (qrc-file). Putting it into the resources does not imply that you use the compiler.
Then there is the JIT compiler, that might (on supported platforms) do a Just-in-Time-Compilation. More on this here
I seldom see static analyzer for functional programming languages, like Racket/Scheme, I even doubt that whether there are any. I would like to write a static analyzer for functional languages, say Scheme/Racket. How should I go about it?
Yes, there is some work on static analysis of dynamic languages like Scheme. For instance, see the work of Olin Shivers (http://www.ccs.neu.edu/home/shivers/citations.html) and Manuel Serrano (http://www-sop.inria.fr/members/Manuel.Serrano/index-1.html).
There's already, e.g., typed racket: http://docs.racket-lang.org/ts-guide/index.html
Since valid racket code is valid typed racket, you just have to change the language you're working in. Then, for libraries with typed versions, load those instead of the untyped versions, and certain type errors can get caught statically already. Further type annotations can be added to your own code to get guarantees of type correctness beyond that...
First read this paper by Shivers, explaining why there is no static control flow graph available in Scheme.
Might implemented k-CFA in Scheme. Matt Might's site and blog is a good starting point for exploring static analysis of higher-order languages.
I did some static analysis implementations for Scheme in Java as well:
k-CFA implementation
Interprocedural Dependence Analysis implementation based on a paper by Might and Prabhu
I am very new to c++ and confused between what is the difference between modular programming and function oriented programming.I have never done modular programming so I just know modules by definition that it contains functions.So what is the difference between a sequential(function-oriented language)and modular programming?Thanks in advance.
EDIT:
I was reading about C++'s OOP.It started something like what is unstructured programming, than gave a basic idea about structured programming, than modular programming and finally,OOP.
Modular programming is mostly a strategy to reduce coupling in a computer program, mostly by means of encapsulation.
Before modular programming, local coherence of the code was ensured by structured programming, but global coherence was lacking: if you decided that your spell-checking dictionary would be implemented as a red-black tree, then this implementation would be exposed to everyone else in the program, so that the programmer working on, say, text rendering, would be able to access the red-black tree nodes to do meaningful things with them.
Of course, this became hell once you needed to change the implementation of your dictionary, because then you would have to fix the code of other programmers as well.
Even worse, if the implementation detail involved global variables, then you had to be exceedingly careful of who changed them and in what order, or strange bugs would crop up.
Modular programming applied encapsulation to all of this, by separating the implementation (private to the module) from the interface (what the rest of the program can use). So, a dictionary module could expose an abstract type that would only be accessible through module functions such as findWord(word,dictionary). Someone working on the dictionary module would never need to peek outside that module to check if someone might be using an implementation detail.
They are both ways of structuring your code. If your interested in function-oriented programming and want to understand it a bit better, I'd take a look at lisp. C++ isn't truly function oriented as every function should return a value yet C++ functions can return void (making it a procedure rather than a function), so it's not a true functional programming language in the sense.
"I have never done modular programming so I just know modules by definition that it contains functions".
Modules are a level higher than functions.
That's a good start. Think of a function as a unit of work that does something and when you have several functions that you can group in a certain way, you put them in a module. So, string.h has a bunch of functions for working with strings, but you simply include the header and you have access to all those functions directly. You can then reuse those modules in other projects as you'd already used the modules previously and they've been (I assume) debugged and tested and stop people from reinventing the wheel. The whole point is to benefit from the cumulative experience.
I'd suggest you think of a project you'd like and write some functions and think about how you'd like to organize the code for another developer to use.
Hope this is of some use to you.
I believe functional programming leads us to micro services paradigm as for now while modular programming tends to similar to OOP concept.
In QT we can connect signals and slots using the following simple syntax:
connect(pObject1, signal1, pObject2, slot2)
For instance, one can write something like:
A a;
B b;
connect(&a, SIGNAL(valueChanged(int)), &a, SLOT(setValue(int)));
With Boost::Signal the syntax we would write it this way:
A a;
B b;
a.valueChanged.connect(boost::bind(&B::SetValue, &b, _1))
IMHO, the boost signal's syntax is more complicated. Is there a way to make the Boost::Signal's syntax more QT like.
The thing with Qt is that it goes through a code generation phase during compilation, that Boost can't do. That means that Qt can do some very clever syntactic things that can't be copied without going through a similar process.
To quote Wikipedia:
Known as the moc, this is a tool that is run on the sources of a Qt program. It interprets certain macros from the C++ code as annotations, and uses them to generate additional C++ code with "Meta Information" about the classes used in the program. This meta information is used by Qt to provide programming features not available natively in C++: the signal/slot system, introspection and asynchronous function calls.
(I can't get the link to work, but it's http://en.wikipedia.org/wiki/Qt_(framework))
Edit: I think the Wikipedia quote is quite clear that the signal/slot system is implemented using the moc. I doubt very much that there's any way to use the same syntax without using a similar system.
I search for a programming language for which a compiler exists and that supports self modifying code. I’ve heared that Lisp supports these features, but I was wondering if there is a more C/C++/D-Like language with these features.
To clarify what I mean:
I want to be able to have in some way access to the programms code at runtime and apply any kind of changes to it, that is, removing commands, adding commands, changing them.
As if i had the AstTree of my programm. Of course i can’t have that tree in a compiled language, so it must be done different. The compile would need to translate the self-modifying commands into their binary equivalent modifications so they would work in runtime with the compiled code.
I don’t want to be dependent on an VM, thats what i meant with compiled :)
Probably there is a reason Lisp is like it is? Lisp was designed to program other languages and to compute with symbolic representations of code and data. The boundary between code and data is no longer there. This influences the design AND the implementation of a programming language.
Lisp has got its syntactical features to generate new code, translate that code and execute it. Thus pre-parsed code is also using the same data structures (symbols, lists, numbers, characters, ...) that are used for other programs, too.
Lisp knows its data at runtime - you can query everything for its type or class. Classes are objects themselves, as are functions. So these elements of the programming language and the programs also are first-class objects, they can be manipulated as such. Dynamic language has nothing to do with 'dynamic typing'.
'Dynamic language' means that the elements of the programming language (for example via meta classes and the meta-object protocol) and the program (its classes, functions, methods, slots, inheritance, ...) can be looked at runtime and can be modified at runtime.
Probably the more of these features you add to a language, the more it will look like Lisp. Since Lisp is pretty much the local maximum of a simple, dynamic, programmable programming language. If you want some of these features, then you might want to think which features of your other program language you have to give up or are willing to give up. For example for a simple code-as-data language, the whole C syntax model might not be practical.
So C-like and 'dynamic language' might not really be a good fit - the syntax is one part of the whole picture. But even the C syntax model limits us how easy we can work with a dynamic language.
C# has always allowed for self-modifying code.
C# 1 allowed you to essentially create and compile code on the fly.
C# 3 added "expression trees", which offered a limited way to dynamically generate code using an object model and abstract syntax trees.
C# 4 builds on that by incorporating support for the "Dynamic Language Runtime". This is probably as close as you are going to get to LISP-like capabilities on the .NET platform in a compiled language.
You might want to consider using C++ with LLVM for (mostly) portable code generation. You can even pull in clang as well to work in C parse trees (note that clang has incomplete support for C++ currently, but is written in C++ itself)
For example, you could write a self-modification core in C++ to interface with clang and LLVM, and the rest of the program in C. Store the parse tree for the main program alongside the self-modification code, then manipulate it with clang at runtime. Clang will let you directly manipulate the AST tree in any way, then compile it all the way down to machine code.
Keep in mind that manipulating your AST in a compiled language will always mean including a compiler (or interpreter) with your program. LLVM is just an easy option for this.
JavaScirpt + V8 (the Chrome JavaScript compiler)
JavaScript is
dynamic
self-modifying (self-evaluating) (well, sort of, depending on your definition)
has a C-like syntax (again, sort of, that's the best you will get for dynamic)
And you now can compile it with V8: http://code.google.com/p/v8/
"Dynamic language" is a broad term that covers a wide variety of concepts. Dynamic typing is supported by C# 4.0 which is a compiled language. Objective-C also supports some features of dynamic languages. However, none of them are even close to Lisp in terms of supporting self modifying code.
To support such a degree of dynamism and self-modifying code, you should have a full-featured compiler to call at run time; this is pretty much what an interpreter really is.
Try groovy. It's a dynamic Java-JVM based language that is compiled at runtime. It should be able to execute its own code.
http://groovy.codehaus.org/
Otherwise, you've always got Perl, PHP, etc... but those are not, as you suggest, C/C++/D- like languages.
I don’t want to be dependent on an VM, thats what i meant with compiled :)
If that's all you're looking for, I'd recommend Python or Ruby. They can both run on their own virtual machines and the JVM and the .Net CLR. Thus, you can choose any runtime you want. Of the two, Ruby seems to have more meta-programming facilities, but Python seems to have more mature implementations on other platforms.