e.g. named this pointer as this.

def fibonacci
  memo = [0, 1]
  ->(n) { memo[n] ||= this.call(n-1) + this.call(n-2) }
end

fibonacci.call(100) # => 354224848179261915075

instead of:

def fibonacci
  memo = [0, 1]
  feb  = ->(n) { memo[n] ||= feb.call(n-1) + feb.call(n-2) }
  feb
end

fib.call(100) # => 354224848179261915075