Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:D
['AB A2 FG F2 D>D ED CD', 'A2 F3 F GF E2 E3 G']  
X:1
L:1/8
M:4/4
K:D
 AB A2 FG F2 | D>D ED CD G2 | GA G>F EF E2 | A2 cB AG F2 | AB A2 FG F2 | D>D ED CD B2 | 
 GB B>G FA A2 | Ad cB GE DA, || DF | A2 A3 B AB | A2 F3 F GF | E2 E3 G FE | DA/B/-B/A/F DA, DF | 
 A2 A3 BAB | A2 F3 F GF | E2 E3 G FE | DA/B/-B/A/F D2 D ||  