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
['GBAG FE E2 FGAF GABd', 'defg a^gab afdf bagf e^def gBgf gbag', 'cdef g=c(3ccc gbag |1 fgef defg :|2']  
X:1
L:1/8
M:4/4
K:D
 dB | AGFA BdAF | GBAG FE E2 | FGAF GABd | gfec dcdB | AF(3FFF BFAF | GBAG FE E2 | FGAF GABd | 
 gfec defg |: a^gab afdf | bagf e^def | gBgf gbag |1 fgef defg :|2 fgef dcdB |: ad(3ddd adbd | 
 ad(3ddd cdef | g=c(3ccc gbag |1 fgef defg :|2 fgef dcdB ||  