Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/8=180
M:4/4
K:D
['F3 G AFDE F2 EA FDDE FEFG', 'd3 A FGAB']  
X:1
L:1/8
Q:1/8=180
M:4/4
K:D
 F3 G AFDE | F2 EA FDDE | FEFG AFDE | FAEA D3 z :| d3 A FGAB | A2 dA (3Bcd ec | d3 A FGAB | 
 AFGE FD D2 :|  