Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:C
['(a/f/) ecA', 'cAc ece fdf e2 (a/f/)']  
X:1
L:1/8
M:4/4
K:C
[M:6/8][K:A] .abc (a/f/) | ecA A2 c | BGE E2 (a/f/) | ecA Ace | fba g2 (a/f/) | ecA ABc | 
 BGE E2 E | FGA BGE | A3 A2 :: e | cAc ece | fdf e2 (a/f/) | ecA ABc | BGE E2 (e/d/) | cAc ece | 
 fdf e2 (a/f/) | ecAEFG | A3 A2 :|  