Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:2/4
K:G
['g2 (b/a/g/f/) gdBG ce- ed/c/ BGFD GB-', 'D2 de =f2 ecBc e^f g2 fd^cd', 'A B2 G AFD', 'def gag fdB']  
X:1
L:1/8
M:2/4
K:G
|: g2 (b/a/g/f/) | gdBG | ce- ed/c/ | BGFD | GB- BA/G/ | (c/d/e/f/) g2 | fdA^c | d2 D2 :: de =f2 | 
 ecBc | e^f g2 | fd^cd | ab c'2 | bfge | dBcA | G2 G2 ::[M:6/8][K:G] GAB c2 A | B2 G AFD | 
 GAB c2 e | dcB A3 | GAB c2 A | B2 G AFD | E3 GAB | cAF G3 :: GAB c2 A | def g3 | def gag | 
 fdB c2 e | def gag | fdB cAF | E3 GAB | cAF G3 :|  