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## standard
func fib(n: Natural): Natural =
if n < 2:
return n
else:
return fib(n-1) + fib(n-2)
## tail-recursive
func fib2(n: int, a = 0, b = 1): int =
if n == 0: a else: fib2(n-1, b, a+b)
## iterable
iterator fib3: int =
var a = 0
var b = 1
while true:
yield a
swap a, b
b += a
## compile-time, list stuff
import std/sugar
static:
proc scan[T, U](list: var seq[T], first, second: U, fun: (U, U) -> U) =
var prev = (first, second)
for i, elem in list:
list[i] = fun(prev[0], prev[1])
prev[0] = prev[1]
prev[1] = list[i]
proc fib4(n: int): seq[int] =
result = newSeq[int](n)
result.scan(0, 1, (p, c) => p + c)
## stupid. macro expansions, outputs (0+1)+((0+1)+(0+1)) etc
import std/macros
macro fib5(n: static[int]): untyped =
var a = quote do: 0
var b = quote do: 1
for _ in 0 ..< n:
swap a, b
b = infix(a, "+", b)
return a
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