uint16_t get_alt_repeat_key_keycode_user(uint16_t keycode, uint8_t mods) {
    bool shifted = (mods & MOD_MASK_SHIFT);  // Was Shift held? - get_oneshot_mods() ???
    switch (keycode) {
        case KC_G:
            if (shifted) {
                return SEND_STRING(SS_TAP(X_BSPC)"Qu"); break;  // Erase the G and send an upper case Qu.
            } else {                                            // Otherwise, the last key was lower case g,
                return SEND_STRING(SS_TAP(X_BSPC)"qu"); break;  // Erase the g and send a lower case qu.
            }
        case KC_J:
            if (shifted) {
                return SEND_STRING(SS_TAP(X_BSPC)"Z"); break;  // Erase the J and send an upper case Z.
            } else {                                           // Otherwise, the last key was lower case j,
                return SEND_STRING(SS_TAP(X_BSPC)"z"); break;  // Erase the j and send a lower case z.
            }
        }
    return KC_TRNS;  // Defer to default definitions

    if (mods & MOD_MASK_CTRL) {  // Was Ctrl held?
        switch (keycode) {
            case KC_G:    return C(KC_Q);  // Ctrl + G reverses to Ctrl + Q
            case KC_J:    return C(KC_Z);  // Ctrl + J reverses to Ctrl + Z
            case KC_EQL:  return C(KC_0);  // Ctrl + = reverses to Ctrl + 0
            case KC_MINS: return C(KC_0);  // Ctrl + - reverses to Ctrl + 0
        }
    }
    return KC_TRNS;  // Defer to default definitions

    switch (keycode) {
        case KC_A:  return KC_N;  // For "An" bigram
        case KC_C:  return KC_E;  // For "Ce" bigram
        case KC_D:  return KC_E;  // For "De" bigram
        case KC_E:  return KC_R;  // For "Er" bigram
        case KC_H:  return KC_E;  // For "He" bigram
        case KC_I:  return KC_N;  // For "In" bigram
        case KC_L:  return KC_O;  // For "Lo" bigram
        case KC_O:  return KC_N;  // For "On" bigram
        case KC_R:  return KC_E;  // For "Re" bigram
        case KC_T:  return KC_H;  // For "Th" bigram
        case KC_U:  return KC_N;  // For "Un" bigram
    }
    return KC_TRNS;  // Defer to default definitions
}

[nix-shell:~/git/qmk_firmware-1]$ qmk compile -kb alps64 -km dlw1789
Ψ Compiling keymap with make -r -R -f builddefs/build_keyboard.mk -s KEYBOARD=alps64 KEYMAP=dlw1789 KEYBOARD_FILESAFE=alps64 TARGET=alps64_dlw1789 INTERMEDIATE_OUTPUT=.build/obj_alps64_dlw1789 VERBOSE=false COLOR=true SILENT=false QMK_BIN="qmk"


avr-gcc (GCC) 8.5.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Size before:
   text    data     bss     dec     hex filename
      0   19942       0   19942    4de6 alps64_dlw1789.hex

Compiling: quantum/keymap_introspection.c                                                          In file included from quantum/quantum.h:154,
                 from ./.build/obj_alps64_dlw1789/src/default_keyboard.h:27,
                 from ./keyboards/alps64/keymaps/dlw1789/keymap.c:22,
                 from quantum/keymap_introspection.c:5:
./keyboards/alps64/keymaps/dlw1789/keymap.c: In function ‘get_alt_repeat_key_keycode_user’:
quantum/send_string/send_string.h:155:29: error: void value not ignored as it ought to be
 #define SEND_STRING(string) send_string_with_delay_P(PSTR(string), 0)
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./keyboards/alps64/keymaps/dlw1789/keymap.c:561:24: note: in expansion of macro ‘SEND_STRING’
                 return SEND_STRING(SS_TAP(X_BSPC)"Qu"); break;  // Erase the G and send an upper case Qu.
                        ^~~~~~~~~~~
quantum/send_string/send_string.h:155:29: error: void value not ignored as it ought to be
 #define SEND_STRING(string) send_string_with_delay_P(PSTR(string), 0)
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./keyboards/alps64/keymaps/dlw1789/keymap.c:563:24: note: in expansion of macro ‘SEND_STRING’
                 return SEND_STRING(SS_TAP(X_BSPC)"qu"); break;  // Erase the g and send a lower case qu.
                        ^~~~~~~~~~~
quantum/send_string/send_string.h:155:29: error: void value not ignored as it ought to be
 #define SEND_STRING(string) send_string_with_delay_P(PSTR(string), 0)
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./keyboards/alps64/keymaps/dlw1789/keymap.c:567:24: note: in expansion of macro ‘SEND_STRING’
                 return SEND_STRING(SS_TAP(X_BSPC)"Z"); break;  // Erase the J and send an upper case Z.
                        ^~~~~~~~~~~
quantum/send_string/send_string.h:155:29: error: void value not ignored as it ought to be
 #define SEND_STRING(string) send_string_with_delay_P(PSTR(string), 0)
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./keyboards/alps64/keymaps/dlw1789/keymap.c:569:24: note: in expansion of macro ‘SEND_STRING’
                 return SEND_STRING(SS_TAP(X_BSPC)"z"); break;  // Erase the j and send a lower case z.
                        ^~~~~~~~~~~
 [ERRORS]
 |
 |
 |
make: *** [builddefs/common_rules.mk:373: .build/obj_alps64_dlw1789/quantum/keymap_introspection.o] Error 1