Programming Language Pragmatics [Chapter 1, Section 1.5] Check Your Understanding

This post has my answers for "Check Your Understanding" questions in section 1.5, Chapter 1 of the book Programming Language Pragmatics by Michael L. Scott.

Chapter 1, Section 1.5 - Check Your Understanding

Question # 11. Explain the distinction between interpretation and compilation. What are the comparative advantages and disadvantages of the two approaches?

Compiler produces machine code from high-level language. After the compilation, the machine code can be directly run on the target system which is locus during runtime. The machine code produced on one architecture cannot be run on a machine with different architecture. The compiled program is faster than its interpreter counterpart.

The interpreter is usually the locus when the program is running. The program written in high-level language is directly run on the target machine through interpreter. In a sense, the high-level code is machine instruction for interpreter. Most of the interpreter are slower in execution as most of the decisions during the course of the program are deferred until the control reaches to the particular statement. However the debugging is much more easier to do in interpreter as interpreter has control throughout the execution of the program. Moreover the interpreter can do useful features like on-the-fly compilation so that the program can generate code during execution which is again consumed/executed by interpreter.

Question #12. Is Java compiled or interpreted (or both)? How do you know?

Java is both compiled and interpreted. Java compiler transforms Java source code to bytecode. Java Virtual Machine (interpreter) executes bytecode.

Question #13. What is the difference between a compiler and a pre-processor?

Pre-processor is needed step before compilation. Compilation transforms the code substantially but pro-processing is usually is light-weight such as removing comments, replacing macros etc.

Question #14. What was the intermediate form employed by the original AT&T C++ compiler?

The intermediate form produced by AT & T C++ compiler is "C".

Questions #15. What is P-code?

P-code is intermediate code that are produced by Pascal compiler. P-code is run by Pascal interpreter during runtime.

Question #16. What is bootstrapping?

Typically the programming language compiler is written by itself meaning that a C compiler is usually written using C. However at first there will not be any compiler to compile the code written in C. Usually a tiny interpreter is written in a different language to produce machine instruction (tiny compiler). Later the tiny compiler produced by interpreter is used to compile the compiler. This is called bootstrapping. In similar fashion more features are added incrementally to produce high quality compiler.

Question #17. What is a just-in-time compiler?

Just-in-time compiler is a feature of interpretor that converts byte-codes to machine instruction while the program is under execution. This is done mainly to increase performance (speed of execution)

Question #18. Name two languages in which a program can write new pieces of itself "on the fly"

List and Prolog (Python, Perl, TCL also have similar features)

Question #19. Briefly describe three "unconventional" compilers - compilers whose purpose is not to prepare a high-level program for execution on a microprocessor

1. SQL - Translates statements to operations on database
2. Compilers to translate logic-level circuit specification into photographic masks for computer chips
3. TEX that translates document to commands for printers

Question #20. List six kinds of tools that commonly support the work of a compiler within a larger programming environment

1. Debuggers
2. Editors
3. Pretty-Printers
4. Style Checkers
5. Configuration Management
6. Profilers

Question #21. Explain how IDEs differs from a collection of command-line tools

All the tools are integrated in an environment often collaborates amongst themselves where as the command line tools are used merely in isolation. For example when a program crashes, IDE points which line of the code is causing the issue and pops up the code in the editor. The developer can make the change and save the file. IDE automatically builds it.

Programming Language Pragmatics [Chapter 1, Section 1.3] Check Your Understanding

This post has my answers for "Check Your Understanding" questions in section 1.3, Chapter 1 of the book Programming Language Pragmatics by Michael L. Scott.

Chapter 1, Section 1.3 - Check Your Understanding

Question #1: What is the difference between machine language and assembly language?

Machine language is written using the instructions set of the processor directly. Each operation supported by the processor is given a code using which the operation is carried out. The code written in Machine language will be in hexadecimal. But in the case of assembly language the program is written using mnemonic (often represented as operations such as MOV, STORE, ADD, SUB etc) which later translated to machine instructions by software called assembler. The assembly language also has provisions for macro definition which expanded by assembler before producing machine code.

Question #2: In what way(s) are high level languages an improvement on assembly language? In what circumstances does it still make sense to program in assembler?

While assembly language is faster to execute, high-level languages can be easily learnt by programmers, ported to varied architecture without requiring to rewrite entire logic on many architectures and saves programmers time since high-level languages are not one-to-one mapping of machine instructions. High level languages often use functions (in the context of mathematical functions) to produce highly expressive code. However assembler will be default choice for system specific performance reasons.

Question #3: Why are there so many programming languages?

There are several programming languages because of the following reasons - evolution, special purpose, personal choice, 

Question #4: What makes a programming language successful?

The programming languages are successful because of one or several of the following reasons - expressive power, Ease of use, ease of implementation, standardization, open source, excellent compilers, economic, patroage and internia.

Question #5: Name three languages in each of the following categories: von Neumann, functional, object-oriented. Name two logic languages. Name two widely used concurrent languages

von Neumann - C, Ada, Fortran

Functional: Haskell, ML, Scheme

Object-oriented: Java, C++, Smalltalk

Logic Languages: Prolog, spreadsheets

Concurrent Languages: C++, Java 

Question #6: What distinguishes declarative languages from imperative languages?

Imperative languages solves a problem by sequence of steps with each steps produces some side effects. The imperative language focuses on how a problem should be solved rather than what to do. The declarative languages on the other hand focuses on what needs to done.

Question #7: What organizations spearheaded the development of Ada?

US Department of Defence

Question #8: What is generally considered the first high-level programming language?

FORTRAN?

Question #9: What was the first functional language?

Lisp, Scheme?

Question #10: Why aren't concurrent languages listed as category in Figure 1.1?

Concurrency support is available in many of languages such as Java, C++ and C. Several concurrency packages are available as language extensions

Self Learning - Resources

After a very long time, writing this post. Stayed away from blogging, primarily because i didn't know what to write. The work kept me busy and so no reading, no browsing and no learning (except work). It is just work, work and more work :-)

Finally got some time off and yesterday i did something which i never did for past many months. I started learning a new programming language. It is Python and i know you are fuming for saying it. It isn't new to many of you but it is new to me. I started to learn python in Code Academy and completed the beginner course in Python. Here is the list of online portal that helps you build your skills.

Hope it is useful to someone out there.

http://www.codecademy.com

https://www.coursera.org

https://www.udemy.com

https://www.codeschool.com

http://www.mysliderule.com
http://java9s.com

If you want to add new skills to your kitty, look at the above places and i am sure you will end up learning more. And additionally, you will get a certificate.

BTW, interesting found PyCon India scheduled coming Sept and hoping to attend the sessions and workshops and you can buy tickets here

Scala - The Scalable Language

I stumbled upon the programming language Scala few months back and haven't got a chance yet to work with Scala (just download Scala last night and installed Eclipse plugin in my laptop this morning). I happen to watch a video on Scala by Martin Odersky. It is a great presentation - both the language and the presenter.

If you are looking for some alternatives for Java, check out Scala. Companies like Twitter and LinkedIn are using Scala in their products and seems like the list is growing day by day.

Scala is both object oriented and functional language and the code compiles into bytecodes which runs on a Java Virtual Machine. The main advantage of writing Scala program is that you will end up writing lesser amount of code as Scala is more expressive than Java. The adoption of Scala is in early stage and i hope (should say, rather want) it replaces Java.

You can find more stuff on Scala from here.

Overview on Scala, might help you to embrace Scala - http://www.youtube.com/watch?v=zqFryHC018k
Geeky Stuff - http://www.scala-lang.org/node/198
Scala Home - http://www.scala-lang.org/

Needless to say, i m so confused on whether i should blog about Java or Scala :-)

First Program in Haskell

Recently, I stumbled upon a new programming paradigm - functional programming. Rather than focusing on variables, we define functions that does something. Without much of theory, let us quickly see an example

Write a program that finds triplets (a, b c) such that a, b and c are sides of a right angle triangle with none of the sides is greater than 20. I tried to write programs in Java and in Haskell as well. Here is the code snippet

Java

public class RightAngleTuples {

public static void main(String[] args) {

printTuples();

}

public static void printTuples() {

for(int c = 1; c <= 10; c++) {

for(int a = 1; a <= c; a++) {

for(int b = 1; b <= a; ++b ) {

if(a*a + b*b == c*c && a+b+c == 24) {

System.out.println(a + ", " + b + ", " + c);

}

}

}

}

}

}

Haskell

 Prelude> let triples = [(a,b,c) | c <- [1..10], a <- [1..c], b <- [1..a], a^2 + b^2 == c^2, a+b+c == 24 ]

Prelude> triples

[(8,6,10)]

Initially it may appear that both the programs are different syntactically. But if you really see, while programming in an imperative languages, we need to think a lot of logic and variables (or memory location) that maintains the state of the program. It is programmers responsibility to keep the state sane. But in the case of functional programming, there is no concept of state. Everything is functions (obviously everything is logic).

If you are really interested to learn a new programming paradigm, i recommend Haskell. With my few hours of encounter with Haskell, i feel it changes one's thinking :-) and Learn you a Haskell for Great Good by Miran Lipovaca can be a great resource. (BTW, i copied the above example from the book and i promise that it is in fact last example that i will steal from the book). An heads-up: reading Haskell doesn't increase your value in job market :-), you cannot ask for 40% more hike but just improves your geeky quotient :-)

More stuffs on Haskell in coming weeks/months. Sharing never hurts :-) 

Importance of Expressiveness in Programming Languages

It is a while i had a post here and in fact this is my first post in 2011. I happy to have my first post of the year on the topic that is of huge interest to me these days.

Why aren't we still programming in assembly languages? The threads, inter-process communication mechanisms can be done in assembly language but not easily though. With assembly language, there is only level of abstraction - ability to see the requirements as sequence of bits that are comprehensible by the machine. When you want make your program to run in another target platform, you may need to change both the abstraction and implementation. The assembly language is not as expressive as procedural language. In order to increment a number, you have locate the address, move it to accumulator, add it by one and store back to the same memory location. There is no clear division of responsibility. You have more number of steps to do in assembly but that is very primitive in procedural language.

Why aren't we writing program with procedural language alone? Procedural language is less expressive than object oriented program. The amount of code that a developer should write to accomplish a logic is more in the case of procedural language. While the level of abstraction is moved a level up from the bare machine, still the abstraction is not efficient to solve a problem in application domain. As far as the application is concerned (and in imperative languages), a task is accomplished with side effects. You call a method and it changes the state of few objects. The data and operation have to cohesive. So, in application development it is highly essential that we glue the data together with operations because these operations are specialized over the data.

There are other types of programming languages like functional programming inspired by lambda calculus and one can write their own language for a particular domain. There is one basic commonality in all types of programming languages - they try to be more expressive to make the life of developers easier. For example, today many developers are thinking about writing concurrent programs not only due to multi-cores being prevalent but also due to modern languages that made multi-threading highly expressive. It is easier to write multi-threaded in Java than in C or assembly.

As we move on, we will see many more expressive language, expressive than Java world and it is part of evolution of programming languages.

The article was written after reading Grady Booch's "OOAD with Application" and first chapter of "Programming Paradigms". Hoping to bring few posts on the subject this year. Watch out this space.