This example is written in a style of literate programming (Knuth 1984). The combined code-blocks in this example compose a compilable source code for “Hello World”. For didactic reasons we don’t always give the listing of an entire source file in one go. In stead, we use a system of references known as noweb (Ramsey 1994).

Inside source fragments you may encounter a line with <<...>> marks like,

#include <cstdlib>
#include <iostream>

<<example-main-function>>

which is then elsewhere specified. Order doesn’t matter,

std::cout << "Hello, World!" << std::endl;

So we can reference the <<hello-world>> code block later on.

int main(int argc, char **argv) {
  <<hello-world>>
}

A definition can be appended with more code as follows (in this case, order does matter!):

return EXIT_SUCCESS;

These blocks of code can be tangled into source files.

References