Creating a Non-Trivial C Program Without Keywords

Writing a non-trivial C program without any C keywords is a challenging task, given that C keywords are fundamental to the language's syntax and functionality. However, it is theoretically possible to create a program that behaves like a C program while avoiding traditional keywords through some creative techniques, such as using macros or manipulating the preprocessor.

Theoretical Possibilities with Macros

Here’s a simple example that demonstrates the use of macros to avoid the use of C keywords:

#define X int#define Y main#define Z return#define A  Y() {    Z A}

Explanation:

int is replaced with X. main is replaced with Y. return is replaced with Z. 0 is replaced with A.

The program defines a main function that returns 0, which is the standard way to indicate successful execution in C. The use of macros allows us to avoid directly writing keywords, but the resulting program still adheres to the structure expected by the C compiler.

Limitations and Challenges

While the example above is trivial, creating a truly non-trivial program that performs meaningful computation without any C keywords would require further abstraction and creativity. Here are some key limitations:

Non-Triviality

The example provided is simple and does not demonstrate advanced features of C, such as complex data structures or more intricate control flow.

Readability and Maintainability

Such a program would be difficult to read and maintain as the use of macros obscures the intent.

Compiler Dependency

This approach relies on the preprocessor and may not be portable across different compilers.

In conclusion, while it is possible to create a C program without using keywords through the use of preprocessor directives, the program's complexity and readability would be significantly impacted.

Flexibility Through Preprocessor Directives

Under certain stipulations, such as the use of implicit int and the inclusion of non-keyword preprocessor directives, you have a lot of flexibility. For example:

You can declare variables of type int by merely uttering their name in the right context. For example, if you say x at file scope, you've declared an int variable named x. Looping constructs can be replaced with recursion terminated by ~. Neither ~ nor ~ is a keyword. They're both part of an operator. Similarly, you can create if-then style conditionals without the keyword if.

For instance, you can use arrays of function pointers instead of if-then or switch-case. Additionally, short-circuit evaluation ? and ? provide another means to implement if-then and terminate recursion.

A Non-Trivial Sieve of Eratosthenes Program

Here is a C89 program that uses no C keywords from C89, C99, or C11, implementing the Sieve of Eratosthenes over the numbers less than 1000:

#include stdio.hx[1000]* x[N] nonzero means _stepmark_currmark {    x[mark_curr]  1    mark_curr  mark_step    mark_curr  1000  mark~ 0}iox_curriterate_over_x {    mark_step  iox_curr    mark_curr  2*iox_curr    x[iox_curr]  0  mark~ 0    iox_curr    iox_curr  500  iterate_over_x~ 0}print_currprint_prime {    printf}print_primes {    x[print_curr]  0  print_prime~ 0    print_curr    print_curr  1000  print_primes~ 0}main {    x[0]  1    x[1]  1    iox_curr  2    iterate_over_x    print_curr  2    print_primes}

I'm sure with some effort, this could be optimized quite a bit. This was seriously the first thing that I came up with.

The program is a non-trivial C program which uses no C keywords. Enjoy!

Further Optimization

For an even more obscure version, check out this one I put together in the comments that doesn't even require digits.

Finally, here is a version that eliminates the assignment operator:

#include stdio.hdefine z !__LINE__define o !zdefine t oodefine max ttt - ttttt  ttttttttttdefine QQq qdefine Qq QQqx[max]markcurrstep {    sscanfQ__LINE__    curr  step  max  markcurr  step step}iteratestep {    x[step]  markstep  step step    step  o  max/t  iteratestep  o}print_primesp {    x[p]  printf    p  o  max  print_primesp  o}main {    iteratet    print_primest}

This is a highly obfuscated and optimized version.