Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:2/2
K:G
['D2 (3FED', 'fdcA dg{a}gf']  
X:1
L:1/8
M:2/2
K:G
 D2 | GBAF G2 AF | D2 (3FED ADFD | DGGF GABc | dcde fdcA | GBAF GBAF | D2 (3FED ADGF | 
 DG{A}GF GABc | dfeg fdcA || dg{a}gf gbag | fd (3ddd fdcA | dg{a}gf g2 fg | agbg ag{a}gf | 
 dg{a}gf gbag | fgef defg | (3agf ge fdec | dfeg fdcA ||  