Learning how programming languages work

Question

I\'ve been programming for years (mainly Python), but I don\'t understand what happens behind the scenes when I compile or execute my code.

In the vein of a question I a

Answer 1

In basic terms, you write source files. These are fancy text files, which are taken in by the compiler which outputs some form of executable code (what executes it depends on the type of code you're talking about). The compiler has several parts:

• Some form of preprocessing on the file which handles macros and the like (like from C).
• A parser, which takes in source files, verifies that they conform to the syntactic rules of your language, and transforms the file into an in-memory data structure that is more easily manipulable by other parts of the program. This is called an Abstract Syntax Tree or AST.
• Some form of AST analysis, which verifies that the actual code you wrote does not violate any rules of the language (e.g. recursion in a language that does not support it), as well as many other things.
• Optimization such as tail call optimization, loop optimization, and many other kinds of optimizations.
• Code generation, which is the actual process of taking the final AST and any other generated data and turning it into a binary file of some sort that can be executed or interpreted.

Interpreter:

An interpreter is a program that takes in some form of binary data that represents a program not compiled to code directly executable by the target machine, and runs the commands within. Examples are python, java, and lua.

Native code:

This is code that has been compiled into native instructions directly executable by the target machine. For instance; if you run on an x86 architecture then c++ will compile to an executable file that is understandable by the processor.

Virtual Machine:

This is generally a program built to simulate the construction and operation of a processor. It may be as simple as a program that reads in bytecode and runs native language operations based on the commands the bytecode represents (though calling this a virtual machine may be a stretch), or it may be as complex as completely simulating the behavior of a processor and all associated peripherals.

those other answers have good points in them but this info and links ought to get you started. Any other questions, just ask!

(Most of this article was written with the help of wikipedia though some was written from memory)

Answer 2

You can find many lectures .For example at Itunes U

Answer 3

When I learned about programming, somewhere in the second half of the previous century, I learned that everything needs to be converted to machine code. Script languages would just decide which code to call based upon the scripted code. Compiled code would first be compiled to p-code, which stands for pre-compiled code, which needs to be linked to other precompiled code to create a full application. I liked Turbo Pascal back then, simply because Turbo Pascal compiled directly to machione code and it didn't use the intermediate p-code in-between. That is, until Turbo Pascal 4.0, which created *.tpu compiled units. Most other compilers would compile to the .obj format instead.

When Java was created, something relatively new started to become popular. Basically, a Java compiler just compiles code to some binary script file. This script could then be interpreted, although that mechanism soon changed too.

Nowadays, interpreters are nearly extinct. Most scripted languages will first be compiled to machine code, the machine code is then stored in some cache and thus it can be executed real fast, without the system having to re-interpret any repeating instructions. This works well for text and binary scripts. PHP would be an example of a text-based script. Java and .NET are binary scripts, since you generally compile the code to this binary script format. (They'll call it different, but I think binary scripts sounds better.)

In general, the trick is to convert the code to machine code, using whatever means possible. There have been many ways to do so and it's a bit complex to make it all clear.

I also remember the time when I could write a C++ application where SQL statements would be located inside the code itself. This was very practical too, but it required a preprocessor which would first parse the SQL statements from the code to convert this to other C++ statements and by replacing the SQL statements with those more complex C++ commands. Then the whole thing would be compiled to p-code. Then you'd need to link it with the additional SQL libraries and finally you had an executable.

Answer 4

http://en.wikipedia.org/wiki/Dragon_Book_(computer_science) will explain a lot of those concepts, you should give it a read, it was a real eye opener for me.

Answer 5

compilers, interpreters and virtual machines are just examples of implementation details. What you might look for is programming languages theory, generative grammar, language translators, and you need possibly some computer architecture to relate theory with implementations.

Personally, I learned from Sebesta's book. It gives a very wide introduction to the subject without going into minute details. It also, has a good chapter on the history of programming languages (~20 languages ~3 papers per language). It has nice explanation about grammars and theory of languages in general. Also, It gives a good introduction into Scheme, Prolog, and programming paradigms (Logic, Functional, Imperative^, Object oriented).

^ It concentrate a lot more on the imperative paradigm than the first two.

Answer 6

This series of lectures from Stanford covers several programming languages down to the bits and bolts, including Python (though I've only watched a couple of the C ones).