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Elixir has no traditional for loop — there's no mutable counter to advance. Instead you use recursion (with the Enum module wrapping common patterns).

Recursion:

defmodule Sum do
    def to_n(0), do: 0
    def to_n(n), do: n + to_n(n - 1)
end

IO.puts Sum.to_n(5)   # 15

Multiple function clauses with different patterns let recursion read like math definitions.

Enum is the everyday tool for collection iteration:

Enum.map([1, 2, 3], fn n -> n * 2 end)    # [2, 4, 6]
Enum.filter([1, 2, 3, 4], &(&1 > 2))       # [3, 4]
Enum.reduce([1, 2, 3], 0, &+/2)            # 6
Enum.sum(1..100)                            # 5050

&(&1 + 1) is the capture form — shorthand for fn x -> x + 1 end.