Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/2=100
M:4/4
K:C
['eaga eaga', 'ceAe ceAe', 'aece aece']  
X:1
L:1/8
Q:1/2=100
M:4/4
K:C
 C |[K:A] ad"B" f | eaga eaga | eaga fedc | dfBf dfBf | dfBf edcB | eaga eaga | eaga fedc | 
 defg a2 gf | edcB A3 :: z | ceAe ceAe | ceAe fedc | dfBf dfBf | dfBf edcB | ceAe ceAe | 
 ceAe fedc | defg a2 gf | edcB A3 :: g | aece aece | aece agfe | bfdf bfdf | bfdf bagf | 
 aece aece | aece aedc | defg a2 gf | edcB A3 :|  