• Tagged template string composite()
• Takes any number of elements: regex, constant string, array of strings, or generator function.
• Transforms into generator function. Requires no changes to parser.

Example:

function* AlbumID() {...}
const songIDRegex = /^\d+/;
function* GetSong() {
 const [albumID, [songID]] = yield composite`/album/${AlbumID}/song/${songIDRegex}`;
}