/ longest palindromic substring

s:{,/{(!#x)_\:x:!x}'!1+#x}
f:{a c?|/c:#:'a@:&a~'|:'a:x s x}

"bab"~f"babad"  / also "aba"
"bb"~f"cbbd"

\

charles hall:

f:{
  m:x=/:(!#x)!\:|x  / matches
  i:&:'m            / ones index
  i@:&~0=#:'i       / not empty
  j:&|/'-':'i       / contiguous ones
  k:*>#:'i j        / max
  x i j k}