A-M baby

Task/Fibonacci-sequence/Lua/fibonacci-sequence.lua

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+--calculates the nth fibonacci number. Breaks for negative or non-integer n.
+function fibs(n)
+  return n < 2 and n or fibs(n - 1) + fibs(n - 2)
+end
+
+--more pedantic version, returns 0 for non-integer n
+function pfibs(n)
+  if n ~= math.floor(n) then return 0
+  elseif n < 0 then return pfibs(n + 2) - pfibs(n + 1)
+  elseif n < 2 then return n
+  else return pfibs(n - 1) + pfibs(n - 2)
+  end
+end
+
+--tail-recursive
+function a(n,u,s) if n<2 then return u+s end return a(n-1,u+s,u) end
+function trfib(i) return a(i,1,0) end
+
+--table-recursive
+fib_n = setmetatable({1, 1}, {__index = function(z,n) return z[n-1] + z[n-2] end})