###
# Even Fibonacci numbers
# Problem 2
#
# Each new term in the Fibonacci sequence is generated by adding the previous two terms.
# By starting with 1 and 2, the first 10 terms will be:
# 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
# By considering the terms in the Fibonacci sequence whose values do not exceed four million,
# find the sum of the even-valued terms.
###

using Base.Iterators

cache = Dict()
function fib(n)
    if haskey(cache, n)
        return cache[n]
    end
    if n < 3
        return n
    end
    cache[n] = fib(n - 1) + fib(n - 2)
    return cache[n]
end

# https://stackoverflow.com/questions/56137634/function-chaining-in-julia

result = (
    (fib(n) for n in 1:1_000_000)
    |> r -> takewhile(<(4_000_000), r)
    |> r -> Iterators.filter(x -> (x % 2) == 0, r)
    |> sum
)

println(result)