Question: who wrote the song purple rain for prince
[{'answer': 'Prince', 'provenance': [{'wikipedia_id': '2066899', 'title': 'Purple Rain (song)', 'start_paragraph_id': 1, 'start_character': 27, 'end_paragraph_id': 1, 'end_character': 33, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]