[Nickle] Re: [AI] Nickle Growing Pains

[Barton C Massey]

I'm trying to get a paper out, so you get the short version
:-).  Here's a quick example:

  typedef tree;
  typedef union {
      int leaf;
      struct {
	  tree left, right;
      } node;
  } tree;

  tree t = {
      node = { left = { leaf = 5 }, right = { leaf =  3 } }
  };
  t

  tree u = t;
  t.node.left = u;
  t

Run it and you should see

  node = {left = leaf = 5, right = leaf = 3}
  node = {left = node = {left = leaf = 5, right = leaf = 3}, right = leaf = 3}


Not sure where you decided <> was interesting :-).  The deal is
that <> is the "unit" value: the sole value of type "void"
:-).  For example, when you write

  void f() {
  }

you are actually writing shorthand for

  void f() {
    return <>;
  }

since all Nickle functions return a value.  It can
be useful to use the void type with Nickle's disjoint
union types.

  enum { a, b }

is shorthand for

  union { void a, void b }

which should probably make your head hurt :-(.
You can thus say things like

  typedef enum { a, b } e;
  e v;
  v.a = <>;
  union switch(v) {
  case a: printf("a\n"); break;
  case b: printf("b\n"); break;
  }  

which should print

  a  


Have fun with Nickle!

	Bart