On Thu, Apr 5, 2012 at 01:53, Sutherland, Julian <
julian.sutherlan...@imperial.ac.uk> wrote:
> data Tree = Node Left Right | Leaf
>
> Could be converted to a struct in C/C++:
>
> struct Tree {
> struct Tree* left;
> struct Tree* right;
> };
>
Shouldn't this actually be a tagged union? Not that they exist as such in
C/C++, but are easy enough to emulate (minus the extra type checking that
real tagged unions such as even Pascal gives you):
struct Tree {
enum {Node, Leaf} tag;
/* possibly tag sanity checking macros defined here */
union {
struct {
struct Tree *tree_Node_left;
#ifdef HSC_CHECKED
# define tree_left(tree) (tree->tag == Leaf ? _hsc_abort("tree:
Node.left of Leaf") : tree->_tree_Node.tree_Node_left)
#else
# define tree_left(tree) tree->_tree_Node.tree_Node_left
#endif
struct Tree *tree_Node_right;
#ifdef HSC_CHECKED
# define tree_right(tree) (tree->tag == Leaf ? _hsc_abort("tree:
Node.right of Leaf") : tree->_tree_Node.tree_Node_right)
#else
# define tree_right(tree) tree->_tree_Node.tree_Node_right
#endif
} _tree_Node;
/* strictly we can collapse out the union here because Leaf has no
data */
} _tree_data;
Similarly several of your other examples could use a bit more thought.
--
brandon s allbery allber...@gmail.com
wandering unix systems administrator (available) (412) 475-9364 vm/sms
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