diff --git a/splitmemdictrw.hpp b/splitmemdictrw.hpp
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+++ b/splitmemdictrw.hpp
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+/**
+ * Alee Forth: A portable and concise Forth implementation in modern C++.
+ * Copyright (C) 2023  Clyne Sullivan <clyne@bitgloo.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef ALEEFORTH_SPLITMEMDICTRW_HPP
+#define ALEEFORTH_SPLITMEMDICTRW_HPP
+
+#include "alee.hpp"
+
+#include <algorithm>
+
+template<unsigned long int LON, unsigned long int HIN>
+class SplitMemDictRW : public Dictionary
+{
+    uint8_t *lodict;
+    uint32_t hidict;
+
+public:
+    constexpr explicit SplitMemDictRW(uint8_t *lo, uint32_t hi):
+        lodict(lo), hidict(hi) {}
+
+    constexpr SplitMemDictRW(const SplitMemDictRW<LON, HIN>& spd):
+        SplitMemDictRW(spd.lodict, spd.hidict) {}
+    constexpr auto& operator=(const SplitMemDictRW<LON, HIN>& spd) {
+        *this = SplitMemDictRW(spd.lodict, hidict);
+        return *this;
+    }
+
+
+    virtual Cell read(Addr addr) const noexcept final {
+        if (addr < LON)
+            return *reinterpret_cast<const Cell *>(lodict + addr);
+        else
+            return _data20_read_short(hidict + addr - LON);
+    }
+
+    virtual void write(Addr addr, Cell value) noexcept final {
+        if (addr < LON)
+            *reinterpret_cast<Cell *>(lodict + addr) = value;
+        else
+            _data20_write_short(hidict + addr - LON, value);
+    }
+
+    virtual uint8_t readbyte(Addr addr) const noexcept final {
+        if (addr < LON)
+            return lodict[addr];
+        else
+            return _data20_read_char(hidict + addr - LON);
+    }
+
+    virtual void writebyte(Addr addr, uint8_t value) noexcept final {
+        if (addr < LON)
+            lodict[addr] = value;
+        else
+            _data20_write_char(hidict + addr - LON, value);
+    }
+
+    virtual unsigned long int capacity() const noexcept final {
+        return LON + HIN;
+    }
+};
+
+#endif // ALEEFORTH_SPLITMEMDICTRW_HPP
+