If WEBrick is leaking out of control, which it does do all the time, shut it down and restart it.
Ctrl-c + Up + Enter
WEBrick can slow your computer down to a crawl so it is reccomended that you only use it when it's needed. Otherwise just runs tests, WEBrick's leaks are just another great reason to adapt to test driven development.
def foobar(astring, bstring)
Hash.new do |l,(i, j)|
if l.key? [i, j]
a, b = astring[i], bstring[j]
l[[i, j]] = case
when !a, !b then 0
when a == b then 1 + l[[i + 1, j + 1]]
else [ l[[i + 1, j]], l[[i, j + 1]] ].max