Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:3/2
K:F
['GB BG c/B/A/G/ ^FA A^F A2 GB']  
X:1
L:1/8
M:3/2
K:F
|: GB BG c/B/A/G/ | ^FA A^F A2 | GB A/B/c/A/ B/c/d | DG GB AG :|  