Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:D
['AdB AFA', 'Adf a3 abf']  
X:1
L:1/8
M:6/8
K:D
|: AF/G/A AdB | AFA D3 | DFA gfe | fed edB | A3 AdB | AFA D2 f | gfe fed | edA B/c/dB :: Adf a3 | 
 abf a3 | Adf a2 f | gfe fdB | Adf a3 | abf a2 f | gfe fed | edA B/c/dB :|  