Edit, view, and save are different operations

For a menu/editor:

• View: calculate/display from current data; no mutation.

• Edit: mutate a runtime/cache value and mark dirty.

• Save: validate and commit dirty state on an explicit action.

• Cancel: restore the cached original or discard dirty changes.

editor-operations.gpc

int value;
int original_value;
int dirty;
int editor_open;

function editor_enter() {
    original_value = value;
    dirty = FALSE;
    editor_open = TRUE;
}

function editor_change(delta) {
    value = value + delta;
    if(value < 0) value = 0;
    if(value > 100) value = 100;
    dirty = TRUE;
}

function editor_cancel() {
    value = original_value;
    dirty = FALSE;
    editor_open = FALSE;
}

This prevents merely opening a page from changing persistence.