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+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_PY_PAIRHEAP_H
+#define MICROPY_INCLUDED_PY_PAIRHEAP_H
+
+// This is an implementation of a pairing heap.  It is stable and has deletion
+// support.  Only the less-than operation needs to be defined on elements.
+//
+// See original paper for details:
+// Michael L. Fredman, Robert Sedjewick, Daniel D. Sleator, and Robert E. Tarjan.
+// The Pairing Heap: A New Form of Self-Adjusting Heap.
+// Algorithmica 1:111-129, 1986.
+// https://www.cs.cmu.edu/~sleator/papers/pairing-heaps.pdf
+
+#include "py/obj.h"
+
+// This struct forms the nodes of the heap and is intended to be extended, by
+// placing it first in another struct, to include additional information for the
+// element stored in the heap.  It includes "base" so it can be a MicroPython
+// object allocated on the heap and the GC can automatically trace all nodes by
+// following the tree structure.
+typedef struct _mp_pairheap_t {
+    mp_obj_base_t base;
+    struct _mp_pairheap_t *child;
+    struct _mp_pairheap_t *child_last;
+    struct _mp_pairheap_t *next;
+} mp_pairheap_t;
+
+// This is the function for the less-than operation on nodes/elements.
+typedef int (*mp_pairheap_lt_t)(mp_pairheap_t*, mp_pairheap_t*);
+
+// Core functions.
+mp_pairheap_t *mp_pairheap_meld(mp_pairheap_lt_t lt, mp_pairheap_t *heap1, mp_pairheap_t *heap2);
+mp_pairheap_t *mp_pairheap_pairing(mp_pairheap_lt_t lt, mp_pairheap_t *child);
+mp_pairheap_t *mp_pairheap_delete(mp_pairheap_lt_t lt, mp_pairheap_t *heap, mp_pairheap_t *node);
+
+// Create a new heap.
+static inline mp_pairheap_t *mp_pairheap_new(mp_pairheap_lt_t lt) {
+    (void)lt;
+    return NULL;
+}
+
+// Test if the heap is empty.
+static inline bool mp_pairheap_is_empty(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
+    (void)lt;
+    return heap == NULL;
+}
+
+// Peek at the top of the heap.  Will return NULL if empty.
+static inline mp_pairheap_t *mp_pairheap_peek(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
+    (void)lt;
+    return heap;
+}
+
+// Push new node onto existing heap.  Returns the new heap.
+static inline mp_pairheap_t *mp_pairheap_push(mp_pairheap_lt_t lt, mp_pairheap_t *heap, mp_pairheap_t *node) {
+    node->child = NULL;
+    node->next = NULL;
+    return mp_pairheap_meld(lt, node, heap); // node is first to be stable
+}
+
+// Pop the top off the heap, which must not be empty.  Returns the new heap.
+static inline mp_pairheap_t *mp_pairheap_pop(mp_pairheap_lt_t lt, mp_pairheap_t *heap) {
+    return mp_pairheap_pairing(lt, heap->child);
+}
+
+#endif // MICROPY_INCLUDED_PY_PAIRHEAP_H