COMS W4115
Programming Languages and Translators
Lecture 2: September 14, 2009
Language Design Issues

Overview

1. Course project
2. Fundamental elements of programming languages
3. An overview of the C programming language

1. Course Project

• Project description
• Form a team of five to create and implement an innovative little language of your own design.
• Each team member must write at least 500 lines of code for the compiler.
• Project constitutes 40% of final grade.
• Project team: elect one person to serve each of the following functions.
• Project manager
• This person sets the project schedule, holds weekly meetings with the entire team, maintains the project log, and makes sure the project deliverables get done on time.
• Language and tools guru
• This person defines the baseline process to track language changes and maintain the intellectual integrity of the language.
• This person teaches the team how to use various tools used to build the compiler.
• System architect
• This person defines the compiler architecture, modules, and interfaces.
• System integrator
• This person defines the system integration environment and makes sure the compiler components work together.
• Tester and validator
• This person defines the test suites and executes them to make sure the compiler meets the language specification.
• Project due dates and deliverables:
• Oct. 7: Language white paper (written by entire team, 3-4 pages).
• See http://java.sun.com/docs/overviews/java/java-overview-1.html for a sample white paper on Java.
• Nov. 4: Language tutorial (written by entire team, 10-20 pages).
• Chapter 1 of Kernighan and Ritchie is a good model of a language tutorial.
• Describe a few representative programs that illustrate the nature and scope of your language.
• A "hello, world" program is de rigueur.
• Nov. 4: Language reference manual (written by entire team, 20-30 pages).
• Appendix A of Kernighan and Ritchie is a good model.
• Give a complete description of the lexical and syntactic structure of your language.
• Include a full grammar for your language.
• Dec. 7 and 9: Ten-minute project presentations in class.
• Dec. 21-23: Working compiler and demo.
• Dec. 21-23: Final project report due at project demo.
• Let Peter Lu (yl2505@columbia.edu) know by Sep 16 what implementation language you are most comfortable with (e.g., C or Java) and the kinds of areas for which you might be interested in creating a new language. Contact Peter for help on joining a team or finding additional teammates.

2. Fundamental Elements of Programming Languages

• Programming model
• For example, C is an imperative language, designed around the von Neumann model of computation.
• Program structure
• Character set and lexical conventions
• Names, scopes, bindings, and lifetimes
• Data types and operators
• Expressions and assignment statements
• Control flow
• Procedures and control abstraction
• Data abstraction and object orientation
• Concurrency

3. The C Programming Language

• C is a general-purpose programming language, originally developed by Dennis Ritchie at Bell Labs in 1972 for implementing UNIX, but is now widely used for systems and applications development.
• The Microsoft C Language Reference Manual describes C as
"a general-purpose programming language known for its efficiency, economy, and portability. While these characteristics make it a good choice for almost any kind of programming, C has proven especially useful in systems programming because it facilitates writing fast, compact programs that are readily adaptable to other systems. Well-written C programs are often as fast as assembly-language programs, and they are typically easier for programmers to read and maintain."
• See The Development of the C language by Dennis Ritchie for the history surrounding the development of C.
• The original version of C as published in Kernighan and Ritchie, The C Programming Language, Prentice Hall 1978, is called K&R C.
• C was standardized by ANSI in 1989 (and is called C89) and this version was adopted by ISO/IEC in 1990 (commonly called C90). The 1988 edition of Kernighan and Ritchie's The C Programming Language describes the ANSI standard version of C.
• A new international standard for C was created by ISO/IEC in 1999 and is referred to as C99.
• Example source program: Line-counting program in C (from K & R, p. 19).

    #include <stdio.h>

    /* count lines in input */
    main()
    {
      int c, nl;

      nl = 0;
      while ((c = getchar()) != EOF)
        if (c == '\n')
          ++nl;
        printf("%d\n", nl);
    }
  

4. An Overview of the C Programming Language

From Appendix A of Kernighan and Ritchie, 1988.


• Program structure
• Source files and source programs
• A source program consists of one or more source files called translation units.
• A translation unit is the input to the compiler.
• A translation unit is a sequence of external declarations, which are either declarations or function definitions.
• The main function
• Every C program must have one main function, which is where program execution starts.
• You may pass command-line arguments (parameters) to a C program when it begins executing with the syntax

   main(int argc, char *argv[])

• Lifetime, scope, visibility, and linkage
• Lifetime is the period of time during the execution of a program in which a variable or function exists.
• The scope of a name is the region of the program in which it is known (visible). C uses static scope; that is, the scope of a name can be determined at compile time.
• The linkage of a name determines whether the same name in another scope refers to the same variable or function.
• Name spaces
• Identifiers in a C program can fall into several disjoint name spaces. This allows the same identifier to be used for different purposes even in the same scope if the uses are in different name spaces.
• E.g., the three uses of student in this structure declaration are in three different name spaces (structure tag, structure member, structure variable):

   struct student {      /* here student is a structure tag */
      char student[25];  /* here student is a structure member */
         int id;
   } student;            /* here student is a structure variable */

5. Lexical Conventions of C

• Character set
• A C source program contains characters from the source character set, which includes the upper and lowercase letters, digits, underscore, punctuation, and some graphic characters such as space and various kinds of tabs. There are a number of mechanisms to specify various kinds of constants.
• A C target program uses characters from the target character set when it executes in the target environment.
• The source and target character sets are related but need not be the same and can use different encodings.
• See the C99 standard or C characters for more details.
• Tokens
• identifiers
• keywords
• constants
• string literals
• operators
• separators
• whitespace
• Comments
• C89 has the multiple line /* ... */ style comment,
• C99 has added the C++ style // this is a single line comment