Made post order tree traversal

mpc.c

@@ -2808,6 +2808,93 @@ 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:
+            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;
+    }
+
+    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;
+
+    if(*trav == NULL) return NULL;
+
+    switch((*trav)->order) {
+        case mpc_ast_trav_order_pre:
+            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;
+            }
+    }
+
+    return ret;
+}
+
 mpc_val_t *mpcf_fold_ast(int n, mpc_val_t **xs) {
   
   int i, j;

mpc.h

@@ -281,6 +281,23 @@ 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);
+
 /*
 ** Warning: This function currently doesn't test for equality of the `state` member!
 */