Boléro - Wikipedia
Sounds like an exercise, turns out it was!
While on vacation at St Jean-de-Luz, Ravel went to the piano and played a melody with one finger to his friend Gustave Samazeuilh, saying, "Don't you think this theme has an insistent quality? I'm going to try and repeat it a number of times without any development, gradually increasing the orchestra as best I can."[3] Idries Shah wrote that the main theme is adapted from a melody composed for and used in Sufi training.[4]