hello.diderot

#version 1.0
/* ==========================================
## hello.diderot: The usual greeting, in Diderot

<!-- In this and other examples, the code blocks are on lines starting -->
<!-- with a tab character; these are generally intended to be shown as -->
<!-- pre-formatted text blocks via Markdown. The ../gen-readme.sh script -->
<!-- converts the current Diderot comment into the contents of the -->
<!-- README.md in this directory. This script also does some -->
<!-- experimental things to generate a test script .test.sh for each -->
<!-- example; the contents of these test scripts is based on the -->
<!-- (tab-indicated) code blocks herein, but with some modifications. -->
<!-- Those modifications are controlled with the lines starting with -->
<!-- "\t#" (tab pound), which are also processed by -->
<!-- ../gen-readme.sh. These lines (as well as these HTML comments) will -->
<!-- not show up in the generated README.md; but they do control the -->
<!-- contents of the generated .test.sh, which are run as a group with -->
<!-- ../runtests.py -->
<!-- THUS: you can ignore all the \t# lines, and read ./README.md -->
<!-- for the program documentation as it was intended to be seen. -->

You can compile `hello.diderot` with:

	#!
	diderotc --exec hello.diderot
	#prog hello.diderot
and then run it with:

	./hello
	#_junk out.nrrd
After the `hello` executable prints `hello, world`, it saves a single-element
1-D array into `out.nrrd`.  We can inspect its contents with:

	unu save -f text -i out.nrrd
which should print the number 42.
========================================== */

/* Strands normally have parameters, so that different strands can be
   initialized with different values. This unusual case, with only a single
   strand, does not need parameters (and having an unused parameter would
   produce a warning.  */
strand hello () {
   /* Every Diderot program must have at least one output variable. */
   output int out = 42;

   update {
      print("hello, world\n");

      /* this minimal program can be repurposed as a simple expression
         debugging tool. For example, if you were uncertain about the
         order of arguments to atan2(), you could use:

      real a = 0; real b = 1;
      print("atan2(", a, ",", b, ") = ", atan2(a,b), "\n");

         to learn that atan2(0,1) = 0, so its atan2(y,x), like in C. */

      /* The strand runs for only its initial iteration, then stops
         by stabilizing, which stores the final value of the output. */
      stabilize;
   }
}
initially [ hello() | ii in 0..0 ];  // only one strand