opensteno_qmk/keyboards/gboards/g/keymap_combo.h

// Keymap helpers

#define K_ENUM(name, key, ...) name,
#define K_DATA(name, key, ...) const uint16_t PROGMEM cmb_##name[] = {__VA_ARGS__, COMBO_END};
#define K_COMB(name, key, ...) [name] = COMBO(cmb_##name, key),

#define A_ENUM(name, string, ...) name,
#define A_DATA(name, string, ...) const uint16_t PROGMEM cmb_##name[] = {__VA_ARGS__, COMBO_END};
#define A_COMB(name, string, ...) [name] = COMBO_ACTION(cmb_##name),
#define A_ACTI(name, string, ...)         \
    case name:                            \
        if (pressed) SEND_STRING(string); \
        break;
#define BLANK(...)

// Generate data needed for combos/actions
// Create Enum
#undef COMB
#undef SUBS
#define COMB K_ENUM
#define SUBS A_ENUM
enum combos {
#include "combos.def"
};

// Bake combos into mem
#undef COMB
#undef SUBS
#define COMB K_DATA
#define SUBS A_DATA
#include "combos.def"
#undef COMB
#undef SUBS

// Fill combo array
#define COMB K_COMB
#define SUBS A_COMB
combo_t key_combos[] = {
#include "combos.def"
};
#undef COMB
#undef SUBS

// Export length to combo module
int COMBO_LEN = sizeof(key_combos) / sizeof(key_combos[0]);

// Fill QMK hook
#define COMB BLANK
#define SUBS A_ACTI
void process_combo_event(uint8_t combo_index, bool pressed) {
    switch (combo_index) {
#include "combos.def"
    }
}
#undef COMB
#undef SUBS