Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:4/4
K:A
['AAcA AAea', 'fg a2']  
X:1
L:1/8
M:4/4
K:A
 e | AAcA AAea | eAcA BAG>B | AAcA AAea | ecBc AAA :| e | agf>e fg a2 | agfe aece | agfe fg a2 | 
 ecBc AAAe | agf>e fg a2 | agfe aece | fgaf ecaf | ecBc AAA ||  