[Keymap] "Cadet-style" keymap + improved LAYOUT macro for melody96 (#5985)

* [melody96] "Cadet-style" keymap for melody96; LAYOUT macro for hotswap keyboard.

* Rename macro.

* Fix layer types.

5 files changed, 391 insertions, 0 deletions

diff --git a/keyboards/melody96/keymaps/zunger/config.h b/keyboards/melody96/keymaps/zunger/config.h
new file mode 100644
index 0000000000..cc06440e0d
--- /dev/null
+++ b/keyboards/melody96/keymaps/zunger/config.h
@@ -0,0 +1,22 @@
+/* Copyright 2018 MechMerlin
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+// Enable cmd-option-escape on mac.
+#define GRAVE_ESC_ALT_OVERRIDE
+
+// place overrides here
diff --git a/keyboards/melody96/keymaps/zunger/keymap.c b/keyboards/melody96/keymaps/zunger/keymap.c
new file mode 100644
index 0000000000..9031447cd2
--- /dev/null
+++ b/keyboards/melody96/keymaps/zunger/keymap.c
@@ -0,0 +1,250 @@
+/* Copyright 2019 Yonatan Zunger
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include QMK_KEYBOARD_H
+
+enum custom_keycodes {
+  // We provide special layer management keys:
+  //    GREEK triggers the Greek (aka "Front") layer, or the SHIFTGREEK layer when shift is held.
+  //          (Because we use Unicode, we need to implement shift-handling at the firmware level,
+  //          rather than the OS level like we do in the QWERTY layer)
+  //    CADET or GREEK+ALT triggers the Cadet (aka "Top") layer, or the SHIFTCADET layer when
+  //          shift is held.
+  //    LAYER_LOCK locks the "base" layer (i.e., QWERTY, GREEK, or CADET) to the value which is
+  //          pressed at the moment that it is being released. When a layer lock is set, the
+  //          analogous layer modifier key is reversed; e.g., if you lock the GREEK layer, then the
+  //          GREEK button bounces you back to QWERTY.
+  //
+  // We also parse the shift, alt, and caps lock keys to provide management of those which is
+  // compatible with these various layers.
+  KC_GREEK = SAFE_RANGE,
+  KC_CADET,
+  KC_LAYER_LOCK,
+};
+
+enum layers_keymap {
+  _QWERTY = 0,
+  _FUNCTION,
+
+  _GREEK,
+  _SHIFTGREEK,
+  _CADET,
+  _SHIFTCADET,
+};
+
+// This is so that H(xxxx) has the same width as _______, which makes the grids more legible.
+#define H(x) UC(0x##x)
+#define MO_FN MO(_FUNCTION)
+#define KC_LLCK KC_LAYER_LOCK
+
+// TODO: To generalize this, we want some #defines that let us specify how each key on the base
+// layer should map to the four special layers, and then use that plus the base layer definition to
+// autogenerate the keymaps for the other layers.
+// TODO: It would also be nice to be able to put the actual code points in here, rather than
+// numbers.
+// TODO: Also add checkmark and dengir.
+
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+  /* The diagram below shows five rows for each key: from top to bottom, the QWERTY layer, the
+   * GREEK layer, the SHIFTGREEK layer, the CADET layer, and the SHIFTCADET layer. (The single
+   * diagram is to make it easier to see what goes where with this many layers!)
+   *
+   * ,----------------------------------------------------------------------------
+   * | ` |F1 |F2 |F3 |F4 |F5 |F6 |F7 |F8 |F9 |F10|F11|F12|HOM|END|PGU|PGD|MUT|BRK|  QWERTY
+   * | ` | ¹ | ² | ³ | ⁴ | ⁵ | ⁶ | ⁷ | ⁸ | ⁹ | ⁰ | ⁻ | ⁺ | ⁽ | ⁾ |   |   |   |   |  GREEK
+   * | ` | ₁ | ₂ | ₃ | ₄ | ₅ | ₆ | ₇ | ₈ | ₉ | ₀ | ₋ | ₊ | ₍ | ₎ |   |   |   |   |  SHIFTGREEK
+   * | ¬ |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |  CADET
+   * | ∅ |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |  SHIFTCADET
+   * |---------------------------------------------------------------------------|
+   * | ` | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | - | + | BKSPC |LCK| / | * | - |
+   * | ` |   |   |   |   |   |   |   |   |   |   | ∝ | ∼ | BKSPC |LCK| ⊘ | ⊙ | ⊖ |
+   * | ` |   |   |   |   |   |   |   |   |   |   |   | ≁ | BKSPC |LCK|   | ⊗ |   |
+   * |   |   |   |   |   |   |   |   |   |   |   |   | ± | BKSPC |LCK|   |   |   |
+   * |   |   |   |   |   |   |   |   |   |   |   |   | ∓ | BKSPC |LCK|   |   |   |
+   * |---------------------------------------------------------------------------|
+   * | TAB  | Q | W | E | R | T | Y | U | I | O | P | [ | ] |  \ | 7 | 8 | 9 |   |
+   * |      | θ | ω | ε | ρ | τ | ψ | υ | ι | ο | π |   |   |    |   |   |   |   |
+   * |      | Θ | Ω | Ε | Ρ | Τ | Ψ | Υ | Ι | Ο | Π |   |   |    |   |   |   |   |
+   * |      | ∧ | ∨ | ∩ | ∪ | ⊂ | ⊃ | ∀ | ∞ | ∃ | ∂ | ∈ |   |    | * | * | * |   | [1]
+   * |      | ℚ |   |   | ℝ | ⊆ | ⊇ |   | ℵ | ∄ |   | ∉ |   |    | * | * | * |   |
+   * |-----------------------------------------------------------------------| + |
+   * | CTRL   | A | S | D | F | G | H | J | K | L | ; | ' |  RET | 4 | 5 | 6 | ⊕ |
+   * | CTRL   | α | σ | δ | φ | γ | η | ϑ | κ | λ | ⋯ | ⋅ |  RET |   |   |   |   |
+   * | CTRL   | Α | Σ | Δ | Φ | Γ | Η |   | Κ | Λ | … | ∴ |  RET |   |   |   |   |
+   * | CTRL   | ⟘ | ⊤ | ⊢ | ⊣ | ↑ | ↓ | ← | → | ↔ |   |   |  RET | * | * | * |   | [1]
+   * | CTRL   | Å |   | ∇ |   | ⇑ | ⇓ | ⇐ | ⇒ | ⇔ |   |   |  RET | * | * | * |   |
+   * |-----------------------------------------------------------------------|---|
+   * | SHIFT   | Z | X | C | V | B | N | M | , | . | / |SHFT | ↑ | 1 | 2 | 3 |   |
+   * | SHIFT   | ζ | ξ | χ | ς | β | ν | μ | ≪ | ≫ | ∫ |SHFT |   |   |   |   |   |
+   * | SHIFT   | Ζ | Ξ | Χ | ✔ | Β | Ν | Μ | ≲ | ≳ |   |SHFT |   |   |   |   |   |
+   * | SHIFT   |   |   | ≠ | ≈ | ≡ | ≤ | ≥ |   |   | ÷ |SHFT |   | * | * | * |   | [1]
+   * | SHIFT   | ℤ |   | ℂ | ≉ | ≢ | ℕ |   |   |   |   |SHFT |   | * | * | * |   |
+   * |-----------------------------------------------------------------------|ENT|
+   * | CTL | ALT| CMD|         SPACE         | α | β | γ | ← | ↓ | → | 0 | . |   | [2]
+   * | CTL | ALT| CMD|         SPACE         | α | β | γ |   |   |   |   |   |   |
+   * | CTL | ALT| CMD|         SPACE         | α | β | γ |   |   |   |   |   |   |
+   * | CTL | ALT| CMD|         SPACE         | α | β | γ |   |   |   |   |   |   |
+   * | CTL | ALT| CMD|         SPACE         | α | β | γ |   |   |   |   |   |   |
+   * `---------------------------------------------------------------------------'
+   *
+   * [1] CADET + numpad moves the mouse. SHIFT+CADET+NUMPAD moves it more quickly. CADET+5
+   * clicks the mouse, and SHIFT+CADET+FIVE right-clicks.
+   * [2] The Greek letters in this row are the three modifier keys (GREEK, CADET, FN),
+   * not the Unicode Greek letters.
+  */
+  // NB: Using GESC for escape in the QWERTY layer as a temporary hack because I messed up the
+  // switch on the KC_GRV key; change back to KC_ESC once this is fixed.
+	[_QWERTY] = LAYOUT_hotswap(
+    KC_GESC, KC_F1,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,   KC_F7,   KC_F8,   KC_F9,   KC_F10,  KC_F11,  KC_F12,  KC_HOME, KC_END,  KC_PGUP, KC_PGDN, KC_MPLY, KC_BRK,
+    KC_GRV,  KC_1,    KC_2,    KC_3,    KC_4,    KC_5,    KC_6,    KC_7,    KC_8,    KC_9,    KC_0,    KC_MINS, KC_EQL,           KC_BSPC, KC_LLCK, KC_PSLS, KC_PAST, KC_PMNS,
+    KC_TAB,  KC_Q,    KC_W,    KC_E,    KC_R,    KC_T,    KC_Y,    KC_U,    KC_I,    KC_O,    KC_P,    KC_LBRC, KC_RBRC,          KC_BSLS, KC_P7,   KC_P8,   KC_P9,
+    KC_LCTL, KC_A,    KC_S,    KC_D,    KC_F,    KC_G,    KC_H,    KC_J,    KC_K,    KC_L,    KC_SCLN, KC_QUOT,                   KC_ENT,  KC_P4,   KC_P5,   KC_P6,   KC_PPLS,
+    KC_LSFT,          KC_Z,    KC_X,    KC_C,    KC_V,    KC_B,    KC_N,    KC_M,    KC_COMM, KC_DOT,  KC_SLSH, KC_RSFT,          KC_UP,   KC_P1,   KC_P2,   KC_P3,
+    KC_LCTL, KC_LALT, KC_LGUI,                            KC_SPC,                             KC_GREEK,KC_CADET,MO_FN,   KC_LEFT, KC_DOWN, KC_RGHT, KC_P0,   KC_PDOT, KC_PENT),
+	[_GREEK] = LAYOUT_hotswap(
+    KC_GRV,  H(00b9), H(00b2), H(00b3), H(2074), H(2075), H(2076), H(2077), H(2078), H(2079), H(2070), H(207b), H(207a), H(207d), H(207e), XXXXXXX, XXXXXXX, XXXXXXX, _______,
+    KC_GRV,  _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, H(221d), H(223c),          _______, _______, H(2298), H(2299), H(2296),
+    _______, H(03b8), H(03c9), H(03b5), H(03c1), H(03c4), H(03c8), H(03c5), H(03b9), H(03bf), H(03c0), KC_LBRC, KC_RBRC,          KC_BSLS, KC_P7,   KC_P8,   KC_P9,
+    _______, H(03b1), H(03c3), H(03b4), H(03c6), H(03b3), H(03b7), H(03d1), H(03ba), H(03bb), H(22ef), H(22c5),                   _______, KC_P4,   KC_P5,   KC_P6,   H(2295),
+    _______,          H(03b6), H(03be), H(03c7), H(03c2), H(03b2), H(03bd), H(03bc), H(226a), H(226b), H(222b), _______,          _______, KC_P1,   KC_P2,   KC_P3,
+    _______, _______, _______,                            _______,                            _______, _______, _______, _______, _______, _______, KC_P0,   KC_PDOT, KC_PENT),
+	[_SHIFTGREEK] = LAYOUT_hotswap(
+    KC_GRV,  H(2081), H(2082), H(2083), H(2084), H(2085), H(2086), H(2087), H(2088), H(2089), H(2080), H(208b), H(208a), H(208d), H(208e), XXXXXXX, XXXXXXX, XXXXXXX, _______,
+    KC_GRV,  _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, XXXXXXX, H(2241),          _______, _______, XXXXXXX, H(2297), XXXXXXX,
+    _______, H(0398), H(03a9), H(0395), H(03a1), H(03a4), H(03a8), H(03a5), H(0399), H(039f), H(03a0), KC_LBRC, KC_RBRC,          KC_BSLS, KC_P7,   KC_P8,   KC_P9,
+    _______, H(0391), H(03a3), H(0394), H(03a6), H(0393), H(0397), XXXXXXX, H(039a), H(039b), H(2026), H(2234),                   _______, KC_P4,   KC_P5,   KC_P6,   H(2295),
+    _______,          H(0396), H(039e), H(03a7), H(2714), H(0392), H(039d), H(039c), H(2272), H(2273), XXXXXXX, _______,          _______, KC_P1,   KC_P2,   KC_P3,
+    _______, _______, _______,                            _______,                            _______, _______, _______, _______, _______, _______, KC_P0,   KC_PDOT, KC_PENT),
+  // TODO: Add mouse keys to keypad.
+	[_CADET] = LAYOUT_hotswap(
+    H(00AC), KC_F1,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,   KC_F7,   KC_F8,   KC_F9,   KC_F10,  KC_F11,  KC_F12,  XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, _______,
+    KC_GRV,  XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, H(00b1),          _______, _______, XXXXXXX, XXXXXXX, XXXXXXX,
+    _______, H(2227), H(2228), H(2229), H(222a), H(2282), H(2283), H(2200), H(221e), H(2203), H(2202), H(2208), XXXXXXX,          XXXXXXX, KC_P7,   KC_P8,   KC_P9,
+    _______, H(22a5), H(22a4), H(22a2), H(22a3), H(2191), H(2193), H(2190), H(2192), H(2194), XXXXXXX, XXXXXXX,                   _______, KC_P4,   KC_P5,   KC_P6,   XXXXXXX,
+    _______,          XXXXXXX, XXXXXXX, H(2260), H(2248), H(2261), H(2264), H(2265), XXXXXXX, XXXXXXX, H(00f7), _______,          _______, KC_P1,   KC_P2,   KC_P3,
+    _______, _______, _______,                            _______,                            _______, _______, _______, _______, _______, _______, KC_P0,   KC_PDOT, KC_PENT),
+	[_SHIFTCADET] = LAYOUT_hotswap(
+    H(2205), KC_F1,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,   KC_F7,   KC_F8,   KC_F9,   KC_F10,  KC_F11,  KC_F12,  XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, _______,
+    KC_GRV,  XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, XXXXXXX, H(2213),          _______, _______, XXXXXXX, XXXXXXX, XXXXXXX,
+    _______, H(211a), XXXXXXX, XXXXXXX, H(211d), H(2286), H(2287), XXXXXXX, H(2135), H(2204), XXXXXXX, H(2209), XXXXXXX,          XXXXXXX, KC_P7,   KC_P8,   KC_P9,
+    _______, H(212b), XXXXXXX, H(2207), XXXXXXX, H(21d1), H(21d3), H(21d0), H(21d2), H(21d4), XXXXXXX, XXXXXXX,                   _______, KC_P4,   KC_P5,   KC_P6,   XXXXXXX,
+    _______,          H(2124), XXXXXXX, H(2102), H(2249), H(2262), H(2115), XXXXXXX, XXXXXXX, XXXXXXX, H(00f7), _______,          _______, KC_P1,   KC_P2,   KC_P3,
+    _______, _______, _______,                            _______,                            _______, _______, _______, _______, _______, _______, KC_P0,   KC_PDOT, KC_PENT),
+
+  // Function layer is mostly for keyboard meta-control operations. Lots of this is just from the
+  // default layout; TODO make it nicer, add Unicode mode switchers.
+	[_FUNCTION] = LAYOUT_hotswap(
+    RESET,   _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, KC_MUTE, KC_VOLD, KC_VOLU, _______, _______, _______,
+    _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______,          _______, _______, _______, _______, _______,
+    _______, RGB_TOG, _______, RGB_MOD, RGB_HUI, RGB_HUD, RGB_SAI, RGB_SAD, RGB_VAI, RGB_VAD, _______, _______, _______,          _______, _______, _______, _______,
+    BL_TOGG, _______, _______, UC_M_OS, UC_M_LN, UC_M_WI, UC_M_BS, UC_M_WC, _______, _______, _______, _______,                   _______, _______, _______, _______, _______,
+    _______,          _______, _______, BL_DEC,  BL_TOGG, BL_INC,  _______, _______, _______, _______, _______, _______,          _______, _______, _______, _______,
+    _______, _______, _______,                            _______,                            _______, _______, _______, _______, _______, _______, _______, _______, _______),
+};
+
+// Layer bitfields.
+#define GREEK_LAYER (1UL << _GREEK)
+#define SHIFTGREEK_LAYER (1UL << _SHIFTGREEK)
+#define CADET_LAYER (1UL << _CADET)
+#define SHIFTCADET_LAYER (1UL << _SHIFTCADET)
+// The layers we don't touch.
+#define LAYER_MASK ~(GREEK_LAYER|SHIFTGREEK_LAYER|CADET_LAYER|SHIFTCADET_LAYER)
+
+bool process_record_user(uint16_t keycode, keyrecord_t *record) {
+  // We track these persistent globals and manage them on our own, rather than trying to rely on
+  // get_mods or the like, because this function is called *before* that's updated!
+  static bool shift_held = false;
+  static bool alt_held = false;
+  static bool greek_held = false;
+  static bool cadet_held = false;
+
+  // These are where we remember the values of lock states.
+  static bool shift_lock = false;
+  static int layer_lock = _QWERTY;
+
+  // Process any modifier key presses.
+  if (keycode == KC_LSHIFT || keycode == KC_RSHIFT) {
+    shift_held = record->event.pressed;
+  } else if (keycode == KC_LALT || keycode == KC_RALT) {
+    alt_held = record->event.pressed;
+  } else if (keycode == KC_GREEK) {
+    greek_held = record->event.pressed;
+  } else if (keycode == KC_CADET) {
+    cadet_held = record->event.pressed;
+  }
+
+  // Now let's transform these into the "cadet request" and "greek request."
+  const bool greek_request = (greek_held && !alt_held);
+  const bool cadet_request = (cadet_held || (greek_held && alt_held));
+
+  // Now, handle the lock keys. We store next_layer_lock in a local variable so that we can
+  // determine the layer to pick right now before we update layer_lock.
+  int next_layer_lock = layer_lock;
+  if (keycode == KC_CAPS) {
+    // If we're in QWERTY mode, caps lock is already going to be managed by the host OS, but by
+    // tracking it ourselves we can also usefully apply it to the GREEK and CADET layers.
+    if (record->event.pressed) {
+      shift_lock = !shift_lock;
+    }
+  } else if (keycode == KC_LAYER_LOCK) {
+    if (record->event.pressed) {
+      if (cadet_request) {
+        next_layer_lock = _CADET;
+      } else if (greek_request) {
+        next_layer_lock = _GREEK;
+      } else {
+        next_layer_lock = _QWERTY;
+      }
+    }
+  }
+
+  // OK! Now we know which buttons are being held, and the current and upcoming states of the locks.
+  // We can compute our new base layer. Remember that the CADET and GREEK keys act as their own
+  // antonyms if they match the layer lock -- e.g., if you have CADET locked, then CADET+X generates
+  // QWERTY-X.
+  int base_layer;
+  if (cadet_request) {
+    base_layer = (layer_lock == _CADET ? _QWERTY : _CADET);
+  } else if (greek_request) {
+    base_layer = (layer_lock == _GREEK ? _QWERTY : _GREEK);
+  } else {
+    base_layer = layer_lock;
+  }
+
+  const bool shifted = (shift_held != shift_lock);
+  int actual_layer;
+  if (base_layer == _CADET) {
+    actual_layer = (shifted ? _SHIFTCADET : _CADET);
+  } else if (base_layer == _GREEK) {
+    actual_layer = (shifted ? _SHIFTGREEK : _GREEK);
+  } else {
+    // We don't do shifting for the QWERTY layer, since for that we emit USB HID codes and shifting
+    // is managed by the host OS.
+    actual_layer = _QWERTY;
+  }
+
+  // And now we can update the layer lock and the actual firmware layer selector.
+  layer_lock = next_layer_lock;
+  layer_state_t new_layer_state = (layer_state & LAYER_MASK) | (1UL << actual_layer);
+  if (new_layer_state != layer_state) {
+    layer_state_set(new_layer_state);
+  }
+
+  // TODO: We can update LED states based on shift_lock (caps), layer_lock (layer lock), and
+  // base_layer (base layer).
+
+  return true;
+}
diff --git a/keyboards/melody96/keymaps/zunger/readme.md b/keyboards/melody96/keymaps/zunger/readme.md
new file mode 100644
index 0000000000..3eb64a2e73
--- /dev/null
+++ b/keyboards/melody96/keymaps/zunger/readme.md
@@ -0,0 +1,78 @@
+* The "Cadet-Style" keymap for the melody96.
+* Author: Yonatan Zunger (zunger@gmail.com)
+
+This is an experimental keymap being used both for practical reasons (as my daily driver) and to
+work out the ideas of a "space-cadet-style" keyboard which can type text and mathematical symbols
+with equal ease. It's designed for anyone who frequently needs to do this outside of a LaTeX
+environment, or for anyone who loves the old "Space Cadet" keyboard! And it works at its best when
+you have actual Cadet keycaps (like SA Symbolics) installed, because those keycaps will actually
+show what you get.
+
+The core idea of this keyboard is that, in addition to a QWERTY base layer and a function layer, it
+supports two additional base layers -- the GREEK layer (the analogue of the Space Cadet "Greek," or
+"Front," keys) and the CADET layer (the analogue of the Space Cadet "Top" keys). These layers use
+Unicode to generate all of the mathematical symbols you can find on a traditional Space Cadet
+layout, plus a bunch of extras.
+
+Because Unicode can't be encoded using the traditional USB HID protocol, QMK does some clever but
+horrifying things to fool your OS. One consequence of this is that the shift key needs to be handled
+by the keyboard firmware, not the host OS. To handle this, we have two additional layers --
+SHIFTGREEK and SHIFTCADET -- and handle the flipping between all of these layers here in the
+firmware.
+
+*The simple bit: Using this layout on a Melody96*
+
+At the core of this layout are three special modifier keys and two special lock keys:
+
+* The GREEK key, to the right of the spacebar, activates the GREEK layer. GREEK+SHIFT activates
+  SHIFTGREEK. These keys generate Greek letters on the letter keys (thus the name), and a few
+  mathematical symbols on other keys. They correspond to the notations on the front of traditional
+  Space Cadet keys; if your capset doesn't include those (alas, most don't), they're the "pretty
+  obvious" mappings.
+* The CADET key, to the right of GREEK, activates the CADET layer. These are the symbols above the
+  letters on a Space Cadet layout. CADET+SHIFT activates the SHIFTCADET layer, with even more
+  symbols.
+* The FUNCTION key, to the right of CADET, activates the function layer. This is where you have a
+  reset mechanism, a selector for which Unicode input type you want, and so on.
+
+Additionally, GREEK+ALT is equivalent to CADET. This is handy for other keyboards where you don't
+have room for this many modifiers.
+
+The lock keys are:
+
+* Caps lock, if you use it, will also act as a "shift lock" for the Greek and Cadet layers. Shift
+  lock is slightly different, in that while it is engaged shift will _dis_engage it; that's actually
+  pretty useful when typing math.
+* An additional "layer lock" key, by default where "num lock" usually goes, will lock the choice of
+  base layer. To use it, hold down any invocation of the GREEK or CADET layers, or none at all, and
+  hit lock; it will then put you in that layer. The corresponding modifier key will then toggle you
+  back to the QWERTY layer. (So for example, if you hit GREEK+LAYER_LOCK and release them, you're
+  now typing in Greek; the GREEK modifier would cause you to type QWERTY momentarily. To go back to
+  ordinary QWERTY mode, you'd just hit LAYER_LOCK again with no modifiers held)
+
+To see the full layout, check out the big comment in keymap.c.
+
+*A less-simple bit: Adapting this to other keyboards*
+
+This is really a canary for generic Cadet implementations. Before this can be made generic, a few
+things will have to happen:
+
+(1) Instead of a fixed keymap, this has to be refactored into some kind of array showing the
+mappings of QWERTY-layer keys onto the appropriate code points in the GREEK and CADET layers, and
+some preprocessor magic needs to auto-transform this plus a traditional keymap for the QWERTY layer
+into keymaps for all five of the core layers. (Function layers would presumably be handled on a
+per-keyboard basis)
+
+(2) The standard mapping of those should have some #define's to control things like whether there
+are physical F-keys (you would probably want to move superscript and subscripts onto the numbers if
+there weren't, and figure out what to do with the non-numeric super/sub keys), whether you actually
+want to enable GREEK+ALT=CADET, and so on;
+
+(3) There should be support for controlling indicator LEDs based on the base layer selection,
+caps/shift lock state, and layer lock state, as well as for triggering audio on transitions;
+
+(4) All the core fancy logic in process_record_user which implements the layer handling should be
+factored out into its own function, so that keyboards can easily reuse that, too.
+
+This is a lovely TODO for future work, and could be particularly fun to go along with new releases
+of SA Symbolics and the like. Anyone interested in such things, ping me!
diff --git a/keyboards/melody96/keymaps/zunger/rules.mk b/keyboards/melody96/keymaps/zunger/rules.mk
new file mode 100644
index 0000000000..a61cfa33fa
--- /dev/null
+++ b/keyboards/melody96/keymaps/zunger/rules.mk
@@ -0,0 +1,2 @@
+# You need Unicode for this map.
+UNICODE_ENABLE = yes        # Unicode
diff --git a/keyboards/melody96/melody96.h b/keyboards/melody96/melody96.h
index f60f054cae..d846fa28da 100644
--- a/keyboards/melody96/melody96.h
+++ b/keyboards/melody96/melody96.h
@@ -25,4 +25,43 @@
 	{ K110,  K111,  K112,  K113,  K114,  K115,  K116,  K117,  K118 }  \
 }
 
+/*
+ * The layout macro for the layout of hotswap keyboards, with illustrative grid of a typical
+ * assignment.
+ * ,---------------------------------------------------------------------------
+ * |ESC|F1|F2 |F3 |F4 |F5 |F6 |F7 |F8 |F9 |F10|F11|F12|PSC|HOM|END|PGU|PGD|DEL|
+ * ,--------------------------------------------------------------------------|
+ * | ` |1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | - | + | BKSPC |NLK| / | * | - |
+ * |--------------------------------------------------------------------------|
+ * | TAB | Q | W | E | R | T | Y | U | I | O | P | [ | ] |  \ | 7 | 8 | 9 |   |
+ * |----------------------------------------------------------------------| + |
+ * | CTRL  | A | S | D | F | G | H | J | K | L | ; | ' |  RET | 4 | 5 | 6 |   |
+ * |----------------------------------------------------------------------|---|
+ * | LSHIFT | Z | X | C | V | B | N | M | , | . | / |RSHFT| ↑ | 1 | 2 | 3 |   |
+ * |----------------------------------------------------------------------|ENT|
+ * |LCTL|LWIN|LALT|         SPACE         |CTL|ALT|FN | ← | ↓ | → | 0 | . |   |
+ * `---------------------------------------------------------------------------
+ */
+#define LAYOUT_hotswap( \
+  K050, K051, K052, K053, K054, K055, K056, K057, K058, K118, K117, K115, K114, K113, K116, K112, K111, K110, K063, \
+  K040, K041, K042, K043, K044, K045, K046, K047, K048, K108, K107, K105, K104,       K106, K102, K101, K100, K064, \
+  K030, K031, K032, K033, K034, K035, K036, K037, K038, K098, K097, K095, K094,       K093, K096, K092, K091,       \
+  K020, K021, K022, K023, K024, K025, K026, K027, K028, K088, K087, K085,             K084, K086, K082, K081, K080, \
+  K010,       K012, K013, K014, K015, K016, K017, K018, K078, K077, K075, K074,       K073, K076, K072, K071,       \
+  K000, K001, K002,                   K006,                   K008, K007, K005, K004, K003, K066, K062, K061, K060  \
+) { \
+	{ K000,  K001,  K002,  K003,  K004,  K005,  K006,  K007,  K008 }, \
+	{ K010,  KC_NO, K012,  K013,  K014,  K015,  K016,  K017,  K018 }, \
+	{ K020,  K021,  K022,  K023,  K024,  K025,  K026,  K027,  K028 }, \
+	{ K030,  K031,  K032,  K033,  K034,  K035,  K036,  K037,  K038 }, \
+	{ K040,  K041,  K042,  K043,  K044,  K045,  K046,  K047,  K048 }, \
+	{ K050,  K051,  K052,  K053,  K054,  K055,  K056,  K057,  K058 }, \
+	{ K060,  K061,  K062,  K063,  K064,  KC_NO, K066,  KC_NO, KC_NO }, \
+	{ KC_NO, K071,  K072,  K073,  K074,  K075,  K076,  K077,  K078 }, \
+	{ K080,  K081,  K082,  KC_NO, K084,  K085,  K086,  K087,  K088 }, \
+	{ KC_NO, K091,  K092,  K093,  K094,  K095,  K096,  K097,  K098 }, \
+	{ K100,  K101,  K102,  KC_NO, K104,  K105,  K106,  K107,  K108 }, \
+	{ K110,  K111,  K112,  K113,  K114,  K115,  K116,  K117,  K118 }  \
+}
+
 #endif