Documentation and source code are written into one source file. The compilable source code and the formatted documentation can be extracted from this file with specific utilities.

The information is presented in a reading order suitable for human consumption. The code is automatically rearranged for computer execution.

The complete commented TeX source code was published in Knuth's *TeX: The program*, volume B of his 5-volume Computers and Typesetting. Knuth had internally used a literate programming system called DOC as early as 1979; he was inspired by the ideas of Pierre Arnoul de Marneffe. The free CWEB, written by Knuth and Levy, is WEB adapted for C, C++ and Java, runs on most operating systems and can produce TeX and PDF documentation. Other implementations of the concept are noweb and FunnelWeb.

Note that all program code in this article is on lines which start with a dash. Everything else is assumed to be comments and will be ignored by the interpreter.

Firstly, in the interests of putting the user at ease, the program will simulate personal interest in the user by asking for their name, accepting the input and generating a greeting based on the input text.

- cls - print text Please type your name: - store input - print Hello there, - print value - print . Nice to meet you. - newline - newline

Continuing the "query-response" mode of operation, prompt the user for the radius of a circle, which is then used to calculate the area of a circle using the standard formula for the area of a circle: A = πr^{2}. Due to syntax limitations, this is done by multiplying the input value by itself, then by π. This calculated value is returned to the user. Note: the value of π used is an approximation that is sufficiently accurate for our purposes.

- print text Let's work out the area of a circle. - newline - print text Please enter the radius of the circle in yards: - store input - multiplyby value - multiplyby 3.14159 - print Thank you - newline - print text The area of the circle is - print value - print text square yards. - newline - newline

Finally we'll ask the user for the required information and work out the area of a rectangle using the standard width by height formula.

- print text Now let's work out the area of a rectangle. - newline - print text Please enter the width of the rectangle in yards: - store input - print text Please enter the length of the rectangle in yards: - multiplyby input - print Thank you - newline - print text The area of the rectangle is - print value - print text square yards. - newline - newline - print text Goodbye,

And that's the program finished.