DAVID LANG first heard Wagner’s “Tristan und Isolde” at the San Francisco Opera in 1974, as an undergraduate student and aspiring composer. This was the first opera ticket — standing room — that he had paid for with his own money, and he arrived well prepared, with a copy of the score and a flashlight to study it by.

“It was a really big deal for me,” Mr. Lang, now 55, said recently, sitting on a sofa in his light-flooded SoHo loft while two parakeets called noisily for attention from another room…

Lang’s newest work, love fail, premieres June 29 at the New Haven International Festival of Arts and Ideas. Performed by the legendary vocal ensemble Anonymous 4, love fail is an evening-length work that weaves together snippets of medieval courtly love narratives, short stories by MacArthur Fellow Lydia Davis, scraps from the libretto of Wagner’s opera Tristan and Isolde, and text by Lang himself.

Out of these sources, Lang has conjured a single story, in which two unnamed lovers meet each other, love each other, and lose each other—not necessarily in that order…