Merge pull request #50 from petermlm/master

Tree Traversal

examples/tree_traversal.c

@@ -5,9 +5,10 @@ int main(int argc, char *argv[]) {
   mpc_parser_t *Input  = mpc_new("input");
   mpc_parser_t *Node  = mpc_new("node");
   mpc_parser_t *Leaf  = mpc_new("leaf");
-  mpc_ast_t *ast, *tree, *child, *child_sub;
+  mpc_ast_t *ast, *tree, *child, *child_sub, *ast_next;
+  mpc_ast_trav_t *trav;
   mpc_result_t r;
-  int index, lb;
+  int index, lb, i;
 
   mpca_lang(MPCA_LANG_PREDICTIVE,
         " node : '(' <node> ',' /foo/ ',' <node> ')' | <leaf>;"
@@ -65,6 +66,51 @@ int main(int argc, char *argv[]) {
     child_sub = mpc_ast_get_child_lb(child, "node|leaf|regex", lb);
   }
 
+  /* Traversal */
+  printf("Pre order tree traversal.\n");
+  trav = mpc_ast_traverse_start(ast, mpc_ast_trav_order_pre);
+
+  ast_next = mpc_ast_traverse_next(&trav);
+
+  while(ast_next != NULL) {
+    printf("Tag: %s; Contents: %s\n",
+      ast_next->tag,
+      ast_next->contents);
+    ast_next = mpc_ast_traverse_next(&trav);
+  }
+
+  mpc_ast_traverse_free(&trav);
+
+  printf("Post order tree traversal.\n");
+
+  trav = mpc_ast_traverse_start(ast, mpc_ast_trav_order_post);
+
+  ast_next = mpc_ast_traverse_next(&trav);
+
+  while(ast_next != NULL) {
+    printf("Tag: %s; Contents: %s\n",
+      ast_next->tag,
+      ast_next->contents);
+    ast_next = mpc_ast_traverse_next(&trav);
+  }
+
+  mpc_ast_traverse_free(&trav);
+
+  printf("Partial traversal.\n");
+
+  trav = mpc_ast_traverse_start(ast, mpc_ast_trav_order_post);
+
+  ast_next = mpc_ast_traverse_next(&trav);
+
+  for(i=0; i<2 && ast_next != NULL; i++) {
+    printf("Tag: %s; Contents: %s\n",
+      ast_next->tag,
+      ast_next->contents);
+    ast_next = mpc_ast_traverse_next(&trav);
+  }
+
+  mpc_ast_traverse_free(&trav);
+
   /* Clean up and return */
   mpc_cleanup(3, Node, Leaf, Input);
   mpc_ast_delete(ast);

mpc.c

@@ -2808,6 +2808,142 @@ mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, const char *tag, int lb) {
   return NULL;
 }
 
+mpc_ast_trav_t *mpc_ast_traverse_start(mpc_ast_t *ast,
+                                       mpc_ast_trav_order_t order)
+{
+  mpc_ast_trav_t *trav, *n_trav;
+  mpc_ast_t *cnode = ast;
+
+  /* Create the traversal structure */
+  trav = malloc(sizeof(mpc_ast_trav_t));
+  trav->curr_node = cnode;
+  trav->parent = NULL;
+  trav->curr_child = 0;
+  trav->order = order;
+
+  /* Get start node */
+  switch(order) {
+    case mpc_ast_trav_order_pre:
+      /* Nothing else is needed for pre order start */
+      break;
+
+    case mpc_ast_trav_order_post:
+      while(cnode->children_num > 0) {
+        cnode = cnode->children[0];
+
+        n_trav = malloc(sizeof(mpc_ast_trav_t));
+        n_trav->curr_node = cnode;
+        n_trav->parent = trav;
+        n_trav->curr_child = 0;
+        n_trav->order = order;
+
+        trav = n_trav;
+      }
+
+      break;
+
+    default:
+      /* Unreachable, but compiler complaints */
+      break;
+  }
+
+  return trav;
+}
+
+mpc_ast_t *mpc_ast_traverse_next(mpc_ast_trav_t **trav) {
+  mpc_ast_trav_t *n_trav, *to_free;
+  mpc_ast_t *ret = NULL;
+  int cchild;
+
+  /* The end of traversal was reached */
+  if(*trav == NULL) return NULL;
+
+  switch((*trav)->order) {
+    case mpc_ast_trav_order_pre:
+      ret = (*trav)->curr_node;
+
+      /* If there aren't any more children, go up */
+      while(*trav != NULL &&
+        (*trav)->curr_child >= (*trav)->curr_node->children_num)
+      {
+        to_free = *trav;
+        *trav = (*trav)->parent;
+        free(to_free);
+      }
+
+      /* If trav is NULL, the end was reached */
+      if(*trav == NULL) {
+        break;
+      }
+
+      /* Go to next child */
+      n_trav = malloc(sizeof(mpc_ast_trav_t));
+
+      cchild = (*trav)->curr_child;
+      n_trav->curr_node = (*trav)->curr_node->children[cchild];
+      n_trav->parent = *trav;
+      n_trav->curr_child = 0;
+      n_trav->order = (*trav)->order;
+
+      (*trav)->curr_child++;
+      *trav = n_trav;
+
+      break;
+
+    case mpc_ast_trav_order_post:
+      ret = (*trav)->curr_node;
+
+      /* Move up tree to the parent If the parent doesn't have any more nodes,
+       * then this is the current node. If it does, move down to its left most
+       * child. Also, free the previous traversal node */
+      to_free = *trav;
+      *trav = (*trav)->parent;
+      free(to_free);
+
+      if(*trav == NULL)
+        break;
+
+      /* Next child */
+      (*trav)->curr_child++;
+
+      /* If there aren't any more children, this is the next node */
+      if((*trav)->curr_child >= (*trav)->curr_node->children_num) {
+        break;
+      }
+
+      /* If there are still more children, find the leftmost child from this
+       * node */
+      while((*trav)->curr_node->children_num > 0) {
+        n_trav = malloc(sizeof(mpc_ast_trav_t));
+
+        cchild = (*trav)->curr_child;
+        n_trav->curr_node = (*trav)->curr_node->children[cchild];
+        n_trav->parent = *trav;
+        n_trav->curr_child = 0;
+        n_trav->order = (*trav)->order;
+
+        *trav = n_trav;
+      }
+
+    default:
+      /* Unreachable, but compiler complaints */
+      break;
+  }
+
+  return ret;
+}
+
+void mpc_ast_traverse_free(mpc_ast_trav_t **trav) {
+  mpc_ast_trav_t *n_trav;
+
+  /* Go through parents until all are free */
+  while(*trav != NULL) {
+      n_trav = (*trav)->parent;
+      free(*trav);
+      *trav = n_trav;
+  }
+}
+
 mpc_val_t *mpcf_fold_ast(int n, mpc_val_t **xs) {
   
   int i, j;

mpc.h

@@ -281,6 +281,25 @@ int mpc_ast_get_index_lb(mpc_ast_t *ast, const char *tag, int lb);
 mpc_ast_t *mpc_ast_get_child(mpc_ast_t *ast, const char *tag);
 mpc_ast_t *mpc_ast_get_child_lb(mpc_ast_t *ast, const char *tag, int lb);
 
+typedef enum {
+  mpc_ast_trav_order_pre,
+  mpc_ast_trav_order_post
+} mpc_ast_trav_order_t;
+
+typedef struct mpc_ast_trav_t {
+  mpc_ast_t             *curr_node;
+  struct mpc_ast_trav_t *parent;
+  int                    curr_child;
+  mpc_ast_trav_order_t   order;
+} mpc_ast_trav_t;
+
+mpc_ast_trav_t *mpc_ast_traverse_start(mpc_ast_t *ast,
+                                       mpc_ast_trav_order_t order);
+
+mpc_ast_t *mpc_ast_traverse_next(mpc_ast_trav_t **trav);
+
+void mpc_ast_traverse_free(mpc_ast_trav_t **trav);
+
 /*
 ** Warning: This function currently doesn't test for equality of the `state` member!
 */