# Stream vs. Enum
`Stream` and `Enum` both offer methods to use on enumerable data structures. The difference between them is that Enum is *eager* while Stream is *lazy*. Enum, being **eager**, produces a whole list of numbers after each operation in the script until the result is reached. Conversely, Stream, being **lazy**, creates a stream that represents a function without executing it straight away.

# Why use Streams?
Streams are useful when working with huge, potentially infinite data sets. With large data sets, streams are more suitable as they do not fill up the memory with all the data at once, which Enum would do ​due to its intermediate lists.

range = 1..1_000_000
stream = Stream.map(range, &(&1 * 3))
IO.puts Enum.sum(stream)

ElixirEnvironment

Streams can also be used to produce infinite lists. These lists are not actually infinitely long, but functions can be applied to utilize only the amount of elements needed. Following is an example:

stream = Stream.cycle([1, 2, 3, 4, 5])
IO.inspect Enum.take(stream, 15)

>The `cycle` function creates an infinite stream of a list and the `take` function takes a specified number of elements from the stream.

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When to use Stream in Elixir

Streams in Elixir are preferred for handling large or infinite data sets due to their lazy evaluation, unlike the eager Enum.