Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/4
M:2/2
K:F
['f e d', 'G A']  
X:1
L:1/4
M:2/2
K:F
 f | e d c a | g f e d | e g- g f | e d c a | g f g a | c f- f :: A | B d g G | A c f F | 
 E G- G A | B d g G | A c f g | a f- f :|  