Generative AIs generate documents such as texts or images based on a user-defined text, the prompt. Finding and refining prompts that produce a desired document has become the art of prompt engineering. Generative models do not provide a built-in retrieval model for a user’s information need expressed through prompts. We reframe prompt engineering for generative models as interactive text-based retrieval on a novel kind of "infinite index". We apply these insights for the first time in a case study on image generation.