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|
defmodule Stream do
@moduledoc """
Module for creating and composing streams.
Streams are composable, lazy enumerables. Any enumerable that generates
items one by one during enumeration is called a stream. For example,
Elixir's `Range` is a stream:
iex> range = 1..5
1..5
iex> Enum.map range, &(&1 * 2)
[2, 4, 6, 8, 10]
In the example above, as we mapped over the range, the elements being
enumerated were created one by one, during enumeration. The `Stream`
module allows us to map the range, without triggering its enumeration:
iex> range = 1..3
iex> stream = Stream.map(range, &(&1 * 2))
iex> Enum.map(stream, &(&1 + 1))
[3, 5, 7]
Notice we started with a range and then we created a stream that is
meant to multiply each item in the range by 2. At this point, no
computation was done. Only when `Enum.map/2` is called we actually
enumerate over each item in the range, multiplying it by 2 and adding 1.
We say the functions in `Stream` are *lazy* and the functions in `Enum`
are *eager*.
Due to their laziness, streams are useful when working with large
(or even infinite) collections. When chaining many operations with `Enum`,
intermediate lists are created, while `Stream` creates a recipe of
computations that are executed at a later moment. Let's see another
example:
1..3
|> Enum.map(&IO.inspect(&1))
|> Enum.map(&(&1 * 2))
|> Enum.map(&IO.inspect(&1))
1
2
3
2
4
6
#=> [2, 4, 6]
Notice that we first printed each item in the list, then multiplied each
element by 2 and finally printed each new value. In this example, the list
was enumerated three times. Let's see an example with streams:
stream = 1..3
|> Stream.map(&IO.inspect(&1))
|> Stream.map(&(&1 * 2))
|> Stream.map(&IO.inspect(&1))
Enum.to_list(stream)
1
2
2
4
3
6
#=> [2, 4, 6]
Although the end result is the same, the order in which the items were
printed changed! With streams, we print the first item and then print
its double. In this example, the list was enumerated just once!
That's what we meant when we said earlier that streams are composable,
lazy enumerables. Notice we could call `Stream.map/2` multiple times,
effectively composing the streams and keeping them lazy. The computations
are only performed when you call a function from the `Enum` module.
## Creating Streams
There are many functions in Elixir's standard library that return
streams, some examples are:
* `IO.stream/2` - streams input lines, one by one
* `URI.query_decoder/1` - decodes a query string, pair by pair
This module also provides many convenience functions for creating streams,
like `Stream.cycle/1`, `Stream.unfold/2`, `Stream.resource/3` and more.
Note the functions in this module are guaranteed to return enumerables.
Since enumerables can have different shapes (structs, anonymous functions,
and so on), the functions in this module may return any of those shapes
and that this may change at any time. For example, a function that today
returns an anonymous function may return a struct in future releases.
"""
@doc false
defstruct enum: nil, funs: [], accs: [], done: nil
@type acc :: any
@type element :: any
@type index :: non_neg_integer
@type default :: any
# Require Stream.Reducers and its callbacks
require Stream.Reducers, as: R
defmacrop skip(acc) do
{:cont, acc}
end
defmacrop next(f, entry, acc) do
quote do: unquote(f).(unquote(entry), unquote(acc))
end
defmacrop acc(h, n, t) do
quote do: [unquote(h), unquote(n) | unquote(t)]
end
defmacrop next_with_acc(f, entry, h, n, t) do
quote do
{reason, [h | t]} = unquote(f).(unquote(entry), [unquote(h) | unquote(t)])
{reason, [h, unquote(n) | t]}
end
end
## Transformers
@doc """
Shortcut to `chunk(enum, n, n)`.
"""
@spec chunk(Enumerable.t, non_neg_integer) :: Enumerable.t
def chunk(enum, n), do: chunk(enum, n, n, nil)
@doc """
Streams the enumerable in chunks, containing `n` items each, where
each new chunk starts `step` elements into the enumerable.
`step` is optional and, if not passed, defaults to `n`, i.e.
chunks do not overlap. If the final chunk does not have `n`
elements to fill the chunk, elements are taken as necessary
from `leftover` if it was passed. If `leftover` is passed and
does not have enough elements to fill the chunk, then the chunk is
returned anyway with less than `n` elements. If `leftover` is not
passed at all or is `nil`, then the partial chunk is discarded
from the result.
## Examples
iex> Stream.chunk([1, 2, 3, 4, 5, 6], 2) |> Enum.to_list
[[1, 2], [3, 4], [5, 6]]
iex> Stream.chunk([1, 2, 3, 4, 5, 6], 3, 2) |> Enum.to_list
[[1, 2, 3], [3, 4, 5]]
iex> Stream.chunk([1, 2, 3, 4, 5, 6], 3, 2, [7]) |> Enum.to_list
[[1, 2, 3], [3, 4, 5], [5, 6, 7]]
iex> Stream.chunk([1, 2, 3, 4, 5, 6], 3, 3, []) |> Enum.to_list
[[1, 2, 3], [4, 5, 6]]
"""
@spec chunk(Enumerable.t, pos_integer, pos_integer) :: Enumerable.t
@spec chunk(Enumerable.t, pos_integer, pos_integer, Enumerable.t | nil) :: Enumerable.t
def chunk(enum, n, step, leftover \\ nil)
when is_integer(n) and n > 0 and is_integer(step) and step > 0 do
limit = :erlang.max(n, step)
if is_nil(leftover) do
lazy enum, {[], 0}, fn(f1) -> R.chunk(n, step, limit, f1) end
else
lazy enum, {[], 0},
fn(f1) -> R.chunk(n, step, limit, f1) end,
&do_chunk(&1, n, leftover, &2)
end
end
defp do_chunk(acc(_, {_, 0}, _) = acc, _, _, _) do
{:cont, acc}
end
defp do_chunk(acc(h, {buffer, count} = old, t), n, leftover, f1) do
buffer = :lists.reverse(buffer, Enum.take(leftover, n - count))
next_with_acc(f1, buffer, h, old, t)
end
@doc """
Chunks the `enum` by buffering elements for which `fun` returns
the same value and only emit them when `fun` returns a new value
or the `enum` finishes.
## Examples
iex> stream = Stream.chunk_by([1, 2, 2, 3, 4, 4, 6, 7, 7], &(rem(&1, 2) == 1))
iex> Enum.to_list(stream)
[[1], [2, 2], [3], [4, 4, 6], [7, 7]]
"""
@spec chunk_by(Enumerable.t, (element -> any)) :: Enumerable.t
def chunk_by(enum, fun) do
lazy enum, nil,
fn(f1) -> R.chunk_by(fun, f1) end,
&do_chunk_by(&1, &2)
end
defp do_chunk_by(acc(_, nil, _) = acc, _f1) do
{:cont, acc}
end
defp do_chunk_by(acc(h, {buffer, _}, t), f1) do
next_with_acc(f1, :lists.reverse(buffer), h, nil, t)
end
@doc """
Creates a stream that only emits elements if they are different from the last emitted element.
This function only ever needs to store the last emitted element.
Elements are compared using `===`.
## Examples
iex> Stream.dedup([1, 2, 3, 3, 2, 1]) |> Enum.to_list
[1, 2, 3, 2, 1]
"""
@spec dedup(Enumerable.t) :: Enumerable.t
def dedup(enum) do
dedup_by(enum, fn x -> x end)
end
@doc """
Creates a stream that only emits elements if the result of calling `fun` on the element is
different from the (stored) result of calling `fun` on the last emitted element.
## Examples
iex> Stream.dedup_by([{1, :x}, {2, :y}, {2, :z}, {1, :x}], fn {x, _} -> x end) |> Enum.to_list
[{1, :x}, {2, :y}, {1, :x}]
"""
@spec dedup_by(Enumerable.t, (element -> term)) :: Enumerable.t
def dedup_by(enum, fun) when is_function(fun, 1) do
lazy enum, nil, fn f1 -> R.dedup(fun, f1) end
end
@doc """
Lazily drops the next `n` items from the enumerable.
If a negative `n` is given, it will drop the last `n` items from
the collection. Note that the mechanism by which this is implemented
will delay the emission of any item until `n` additional items have
been emitted by the enum.
## Examples
iex> stream = Stream.drop(1..10, 5)
iex> Enum.to_list(stream)
[6, 7, 8, 9, 10]
iex> stream = Stream.drop(1..10, -5)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]
"""
@spec drop(Enumerable.t, non_neg_integer) :: Enumerable.t
def drop(enum, n) when n >= 0 do
lazy enum, n, fn(f1) -> R.drop(f1) end
end
def drop(enum, n) when n < 0 do
n = abs(n)
lazy enum, {0, [], []}, fn(f1) ->
fn
entry, [h, {count, buf1, []} | t] ->
do_drop(:cont, n, entry, h, count, buf1, [], t)
entry, [h, {count, buf1, [next | buf2]} | t] ->
{reason, [h | t]} = f1.(next, [h | t])
do_drop(reason, n, entry, h, count, buf1, buf2, t)
end
end
end
defp do_drop(reason, n, entry, h, count, buf1, buf2, t) do
buf1 = [entry | buf1]
count = count + 1
if count == n do
{reason, [h, {0, [], :lists.reverse(buf1)} | t]}
else
{reason, [h, {count, buf1, buf2} | t]}
end
end
@doc """
Creates a stream that drops every `nth` item from the enumerable.
The first item is always dropped, unless `nth` is 0.
`nth` must be a non-negative integer, or `FunctionClauseError` will be thrown.
## Examples
iex> stream = Stream.drop_every(1..10, 2)
iex> Enum.to_list(stream)
[2, 4, 6, 8, 10]
iex> stream = Stream.drop_every(1..1000, 1)
iex> Enum.to_list(stream)
[]
iex> stream = Stream.drop_every([1, 2, 3, 4, 5], 0)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]
"""
@spec drop_every(Enumerable.t, non_neg_integer) :: Enumerable.t
def drop_every(enum, 0), do: %Stream{enum: enum}
def drop_every([], _nth), do: %Stream{enum: []}
def drop_every(enum, nth) when is_integer(nth) and nth > 0 do
lazy enum, nth, fn(f1) -> R.drop_every(nth, f1) end
end
@doc """
Lazily drops elements of the enumerable while the given
function returns `true`.
## Examples
iex> stream = Stream.drop_while(1..10, &(&1 <= 5))
iex> Enum.to_list(stream)
[6, 7, 8, 9, 10]
"""
@spec drop_while(Enumerable.t, (element -> as_boolean(term))) :: Enumerable.t
def drop_while(enum, fun) do
lazy enum, true, fn(f1) -> R.drop_while(fun, f1) end
end
@doc """
Executes the given function for each item.
Useful for adding side effects (like printing) to a stream.
## Examples
iex> stream = Stream.each([1, 2, 3], fn(x) -> send self(), x end)
iex> Enum.to_list(stream)
iex> receive do: (x when is_integer(x) -> x)
1
iex> receive do: (x when is_integer(x) -> x)
2
iex> receive do: (x when is_integer(x) -> x)
3
"""
@spec each(Enumerable.t, (element -> term)) :: Enumerable.t
def each(enum, fun) do
lazy enum, fn(f1) ->
fn(x, acc) ->
fun.(x)
f1.(x, acc)
end
end
end
@doc """
Creates a stream that will apply the given function on enumeration and
flatten the result, but only one level deep.
## Examples
iex> stream = Stream.flat_map([1, 2, 3], fn(x) -> [x, x * 2] end)
iex> Enum.to_list(stream)
[1, 2, 2, 4, 3, 6]
iex> stream = Stream.flat_map([1, 2, 3], fn(x) -> [[x]] end)
iex> Enum.to_list(stream)
[[1], [2], [3]]
"""
@spec flat_map(Enumerable.t, (element -> Enumerable.t)) :: Enumerable.t
def flat_map(enum, mapper) do
transform(enum, nil, fn val, nil -> {mapper.(val), nil} end)
end
@doc """
Creates a stream that filters elements according to
the given function on enumeration.
## Examples
iex> stream = Stream.filter([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
iex> Enum.to_list(stream)
[2]
"""
@spec filter(Enumerable.t, (element -> as_boolean(term))) :: Enumerable.t
def filter(enum, fun) do
lazy enum, fn(f1) -> R.filter(fun, f1) end
end
@doc """
Creates a stream that filters and then maps elements according
to given functions.
Exists for symmetry with `Enum.filter_map/3`.
## Examples
iex> stream = Stream.filter_map(1..6, fn(x) -> rem(x, 2) == 0 end, &(&1 * 2))
iex> Enum.to_list(stream)
[4, 8, 12]
"""
@spec filter_map(Enumerable.t, (element -> as_boolean(term)), (element -> any)) :: Enumerable.t
def filter_map(enum, filter, mapper) do
lazy enum, fn(f1) -> R.filter_map(filter, mapper, f1) end
end
@doc """
Creates a stream that emits a value after the given period `n`
in milliseconds.
The values emitted are an increasing counter starting at `0`.
This operation will block the caller by the given interval
every time a new item is streamed.
## Examples
iex> Stream.interval(10) |> Enum.take(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
"""
@spec interval(non_neg_integer) :: Enumerable.t
def interval(n) do
unfold 0, fn(count) ->
:timer.sleep(n)
{count, count + 1}
end
end
@doc """
Injects the stream values into the given collectable as a side-effect.
This function is often used with `run/1` since any evaluation
is delayed until the stream is executed. See `run/1` for an example.
"""
@spec into(Enumerable.t, Collectable.t, (term -> term)) :: Enumerable.t
def into(enum, collectable, transform \\ fn x -> x end) do
&do_into(enum, collectable, transform, &1, &2)
end
defp do_into(enum, collectable, transform, acc, fun) do
{initial, into} = Collectable.into(collectable)
composed = fn x, [acc | collectable] ->
collectable = into.(collectable, {:cont, transform.(x)})
{reason, acc} = fun.(x, acc)
{reason, [acc | collectable]}
end
do_into(&Enumerable.reduce(enum, &1, composed), initial, into, acc)
end
defp do_into(reduce, collectable, into, {command, acc}) do
try do
reduce.({command, [acc | collectable]})
catch
kind, reason ->
stacktrace = System.stacktrace
into.(collectable, :halt)
:erlang.raise(kind, reason, stacktrace)
else
{:suspended, [acc | collectable], continuation} ->
{:suspended, acc, &do_into(continuation, collectable, into, &1)}
{reason, [acc | collectable]} ->
into.(collectable, :done)
{reason, acc}
end
end
@doc """
Creates a stream that will apply the given function on
enumeration.
## Examples
iex> stream = Stream.map([1, 2, 3], fn(x) -> x * 2 end)
iex> Enum.to_list(stream)
[2, 4, 6]
"""
@spec map(Enumerable.t, (element -> any)) :: Enumerable.t
def map(enum, fun) do
lazy enum, fn(f1) -> R.map(fun, f1) end
end
@doc """
Creates a stream that will reject elements according to
the given function on enumeration.
## Examples
iex> stream = Stream.reject([1, 2, 3], fn(x) -> rem(x, 2) == 0 end)
iex> Enum.to_list(stream)
[1, 3]
"""
@spec reject(Enumerable.t, (element -> as_boolean(term))) :: Enumerable.t
def reject(enum, fun) do
lazy enum, fn(f1) -> R.reject(fun, f1) end
end
@doc """
Runs the given stream.
This is useful when a stream needs to be run, for side effects,
and there is no interest in its return result.
## Examples
Open up a file, replace all `#` by `%` and stream to another file
without loading the whole file in memory:
stream = File.stream!("code")
|> Stream.map(&String.replace(&1, "#", "%"))
|> Stream.into(File.stream!("new"))
|> Stream.run
No computation will be done until we call one of the Enum functions
or `Stream.run/1`.
"""
@spec run(Enumerable.t) :: :ok
def run(stream) do
_ = Enumerable.reduce(stream, {:cont, nil}, fn(_, _) -> {:cont, nil} end)
:ok
end
@doc """
Creates a stream that applies the given function to each
element, emits the result and uses the same result as the accumulator
for the next computation.
## Examples
iex> stream = Stream.scan(1..5, &(&1 + &2))
iex> Enum.to_list(stream)
[1, 3, 6, 10, 15]
"""
@spec scan(Enumerable.t, (element, acc -> any)) :: Enumerable.t
def scan(enum, fun) do
lazy enum, :first, fn(f1) -> R.scan_2(fun, f1) end
end
@doc """
Creates a stream that applies the given function to each
element, emits the result and uses the same result as the accumulator
for the next computation. Uses the given `acc` as the starting value.
## Examples
iex> stream = Stream.scan(1..5, 0, &(&1 + &2))
iex> Enum.to_list(stream)
[1, 3, 6, 10, 15]
"""
@spec scan(Enumerable.t, acc, (element, acc -> any)) :: Enumerable.t
def scan(enum, acc, fun) do
lazy enum, acc, fn(f1) -> R.scan_3(fun, f1) end
end
@doc """
Lazily takes the next `count` items from the enumerable and stops
enumeration.
If a negative `count` is given, the last `count` values will be taken.
For such, the collection is fully enumerated keeping up to `2 * count`
elements in memory. Once the end of the collection is reached,
the last `count` elements will be executed. Therefore, using
a negative `count` on an infinite collection will never return.
## Examples
iex> stream = Stream.take(1..100, 5)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]
iex> stream = Stream.take(1..100, -5)
iex> Enum.to_list(stream)
[96, 97, 98, 99, 100]
iex> stream = Stream.cycle([1, 2, 3]) |> Stream.take(5)
iex> Enum.to_list(stream)
[1, 2, 3, 1, 2]
"""
@spec take(Enumerable.t, integer) :: Enumerable.t
def take(_enum, 0), do: %Stream{enum: []}
def take([], _count), do: %Stream{enum: []}
def take(enum, count) when is_integer(count) and count > 0 do
lazy enum, count, fn(f1) -> R.take(f1) end
end
def take(enum, count) when is_integer(count) and count < 0 do
&Enumerable.reduce(Enum.take(enum, count), &1, &2)
end
@doc """
Creates a stream that takes every `nth` item from the enumerable.
The first item is always included, unless `nth` is 0.
`nth` must be a non-negative integer, or `FunctionClauseError` will be thrown.
## Examples
iex> stream = Stream.take_every(1..10, 2)
iex> Enum.to_list(stream)
[1, 3, 5, 7, 9]
iex> stream = Stream.take_every([1, 2, 3, 4, 5], 1)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]
iex> stream = Stream.take_every(1..1000, 0)
iex> Enum.to_list(stream)
[]
"""
@spec take_every(Enumerable.t, non_neg_integer) :: Enumerable.t
def take_every(_enum, 0), do: %Stream{enum: []}
def take_every([], _nth), do: %Stream{enum: []}
def take_every(enum, nth) when is_integer(nth) and nth > 0 do
lazy enum, nth, fn(f1) -> R.take_every(nth, f1) end
end
@doc """
Lazily takes elements of the enumerable while the given
function returns `true`.
## Examples
iex> stream = Stream.take_while(1..100, &(&1 <= 5))
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]
"""
@spec take_while(Enumerable.t, (element -> as_boolean(term))) :: Enumerable.t
def take_while(enum, fun) do
lazy enum, fn(f1) -> R.take_while(fun, f1) end
end
@doc """
Creates a stream that emits a single value after `n` milliseconds.
The value emitted is `0`. This operation will block the caller by
the given time until the item is streamed.
## Examples
iex> Stream.timer(10) |> Enum.to_list
[0]
"""
@spec timer(non_neg_integer) :: Enumerable.t
def timer(n) do
take(interval(n), 1)
end
@doc """
Transforms an existing stream.
It expects an accumulator and a function that receives each stream item
and an accumulator, and must return a tuple containing a new stream
(often a list) with the new accumulator or a tuple with `:halt` as first
element and the accumulator as second.
Note: this function is similar to `Enum.flat_map_reduce/3` except the
latter returns both the flat list and accumulator, while this one returns
only the stream.
## Examples
`Stream.transform/3` is useful as it can be used as the basis to implement
many of the functions defined in this module. For example, we can implement
`Stream.take(enum, n)` as follows:
iex> enum = 1..100
iex> n = 3
iex> stream = Stream.transform(enum, 0, fn i, acc ->
...> if acc < n, do: {[i], acc + 1}, else: {:halt, acc}
...> end)
iex> Enum.to_list(stream)
[1, 2, 3]
"""
@spec transform(Enumerable.t, acc, fun) :: Enumerable.t when
fun: (element, acc -> {Enumerable.t, acc} | {:halt, acc}),
acc: any
def transform(enum, acc, reducer) when is_function(reducer, 2) do
&do_transform(enum, fn -> acc end, reducer, &1, &2, nil)
end
@doc """
Transforms an existing stream with function-based start and finish.
The accumulator is only calculated when transformation starts. It also
allows an after function to be given which is invoked when the stream
halts or completes.
This function can be seen as a combination of `Stream.resource/3` with
`Stream.transform/3`.
"""
@spec transform(Enumerable.t, (() -> acc), fun, (acc -> term)) :: Enumerable.t when
fun: (element, acc -> {Enumerable.t, acc} | {:halt, acc}),
acc: any
def transform(enum, start_fun, reducer, after_fun)
when is_function(start_fun, 0) and is_function(reducer, 2) and is_function(after_fun, 1) do
&do_transform(enum, start_fun, reducer, &1, &2, after_fun)
end
defp do_transform(enumerables, user_acc, user, inner_acc, fun, after_fun) do
inner = &do_transform_each(&1, &2, fun)
step = &do_transform_step(&1, &2)
next = &Enumerable.reduce(enumerables, &1, step)
do_transform(user_acc.(), user, fun, [], next, inner_acc, inner, after_fun)
end
defp do_transform(user_acc, _user, _fun, _next_acc, _next, {:halt, inner_acc}, _inner, after_fun) do
do_after(after_fun, user_acc)
{:halted, inner_acc}
end
defp do_transform(user_acc, user, fun, next_acc, next, {:suspend, inner_acc}, inner, after_fun) do
{:suspended, inner_acc, &do_transform(user_acc, user, fun, next_acc, next, &1, inner, after_fun)}
end
defp do_transform(user_acc, user, fun, next_acc, next, inner_acc, inner, after_fun) do
case next.({:cont, next_acc}) do
{:suspended, [val | next_acc], next} ->
try do
user.(val, user_acc)
catch
kind, reason ->
stacktrace = System.stacktrace
next.({:halt, next_acc})
do_after(after_fun, user_acc)
:erlang.raise(kind, reason, stacktrace)
else
{[], user_acc} ->
do_transform(user_acc, user, fun, next_acc, next, inner_acc, inner, after_fun)
{list, user_acc} when is_list(list) ->
do_list_transform(user_acc, user, fun, next_acc, next, inner_acc, inner,
&Enumerable.List.reduce(list, &1, fun), after_fun)
{:halt, user_acc} ->
next.({:halt, next_acc})
do_after(after_fun, user_acc)
{:halted, elem(inner_acc, 1)}
{other, user_acc} ->
do_enum_transform(user_acc, user, fun, next_acc, next, inner_acc, inner,
&Enumerable.reduce(other, &1, inner), after_fun)
end
{reason, _} ->
do_after(after_fun, user_acc)
{reason, elem(inner_acc, 1)}
end
end
defp do_list_transform(user_acc, user, fun, next_acc, next, inner_acc, inner, reduce, after_fun) do
try do
reduce.(inner_acc)
catch
kind, reason ->
stacktrace = System.stacktrace
next.({:halt, next_acc})
do_after(after_fun, user_acc)
:erlang.raise(kind, reason, stacktrace)
else
{:done, acc} ->
do_transform(user_acc, user, fun, next_acc, next, {:cont, acc}, inner, after_fun)
{:halted, acc} ->
next.({:halt, next_acc})
do_after(after_fun, user_acc)
{:halted, acc}
{:suspended, acc, c} ->
{:suspended, acc, &do_list_transform(user_acc, user, fun, next_acc, next, &1, inner, c, after_fun)}
end
end
defp do_enum_transform(user_acc, user, fun, next_acc, next, {op, inner_acc}, inner, reduce, after_fun) do
try do
reduce.({op, [:outer | inner_acc]})
catch
kind, reason ->
stacktrace = System.stacktrace
next.({:halt, next_acc})
do_after(after_fun, user_acc)
:erlang.raise(kind, reason, stacktrace)
else
# Only take into account outer halts when the op is not halt itself.
# Otherwise, we were the ones wishing to halt, so we should just stop.
{:halted, [:outer | acc]} when op != :halt ->
do_transform(user_acc, user, fun, next_acc, next, {:cont, acc}, inner, after_fun)
{:halted, [_ | acc]} ->
next.({:halt, next_acc})
do_after(after_fun, user_acc)
{:halted, acc}
{:done, [_ | acc]} ->
do_transform(user_acc, user, fun, next_acc, next, {:cont, acc}, inner, after_fun)
{:suspended, [_ | acc], c} ->
{:suspended, acc, &do_enum_transform(user_acc, user, fun, next_acc, next, &1, inner, c, after_fun)}
end
end
defp do_after(nil, _user_acc), do: :ok
defp do_after(fun, user_acc), do: fun.(user_acc)
defp do_transform_each(x, [:outer | acc], f) do
case f.(x, acc) do
{:halt, res} -> {:halt, [:inner | res]}
{op, res} -> {op, [:outer | res]}
end
end
defp do_transform_step(x, acc) do
{:suspend, [x | acc]}
end
@doc """
Creates a stream that only emits elements if they are unique.
Keep in mind that, in order to know if an element is unique
or not, this function needs to store all unique values emitted
by the stream. Therefore, if the stream is infinite, the number
of items stored will grow infinitely, never being garbage collected.
## Examples
iex> Stream.uniq([1, 2, 3, 3, 2, 1]) |> Enum.to_list
[1, 2, 3]
"""
@spec uniq(Enumerable.t) :: Enumerable.t
def uniq(enum) do
uniq_by(enum, fn x -> x end)
end
@doc false
def uniq(enum, fun) do
IO.warn "Stream.uniq/2 is deprecated, use Stream.uniq_by/2 instead"
uniq_by(enum, fun)
end
@doc """
Creates a stream that only emits elements if they are unique, by removing the
elements for which function `fun` returned duplicate items.
The function `fun` maps every element to a term which is used to
determine if two elements are duplicates.
Keep in mind that, in order to know if an element is unique
or not, this function needs to store all unique values emitted
by the stream. Therefore, if the stream is infinite, the number
of items stored will grow infinitely, never being garbage collected.
## Example
iex> Stream.uniq_by([{1, :x}, {2, :y}, {1, :z}], fn {x, _} -> x end) |> Enum.to_list
[{1, :x}, {2, :y}]
iex> Stream.uniq_by([a: {:tea, 2}, b: {:tea, 2}, c: {:coffee, 1}], fn {_, y} -> y end) |> Enum.to_list
[a: {:tea, 2}, c: {:coffee, 1}]
"""
@spec uniq_by(Enumerable.t, (element -> term)) :: Enumerable.t
def uniq_by(enum, fun) do
lazy enum, %{}, fn f1 -> R.uniq_by(fun, f1) end
end
@doc """
Creates a stream where each item in the enumerable will
be wrapped in a tuple alongside its index.
If an `offset` is given, we will index from the given offset instead of from zero.
## Examples
iex> stream = Stream.with_index([1, 2, 3])
iex> Enum.to_list(stream)
[{1, 0}, {2, 1}, {3, 2}]
iex> stream = Stream.with_index([1, 2, 3], 3)
iex> Enum.to_list(stream)
[{1, 3}, {2, 4}, {3, 5}]
"""
@spec with_index(Enumerable.t) :: Enumerable.t
@spec with_index(Enumerable.t, integer) :: Enumerable.t
def with_index(enum, offset \\ 0) do
lazy enum, offset, fn(f1) -> R.with_index(f1) end
end
## Combiners
@doc """
Creates a stream that enumerates each enumerable in an enumerable.
## Examples
iex> stream = Stream.concat([1..3, 4..6, 7..9])
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5, 6, 7, 8, 9]
"""
@spec concat(Enumerable.t) :: Enumerable.t
def concat(enumerables) do
flat_map(enumerables, &(&1))
end
@doc """
Creates a stream that enumerates the first argument, followed by the second.
## Examples
iex> stream = Stream.concat(1..3, 4..6)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5, 6]
iex> stream1 = Stream.cycle([1, 2, 3])
iex> stream2 = Stream.cycle([4, 5, 6])
iex> stream = Stream.concat(stream1, stream2)
iex> Enum.take(stream, 6)
[1, 2, 3, 1, 2, 3]
"""
@spec concat(Enumerable.t, Enumerable.t) :: Enumerable.t
def concat(first, second) do
flat_map([first, second], &(&1))
end
@doc """
Zips two collections together, lazily.
The zipping finishes as soon as any enumerable completes.
## Examples
iex> concat = Stream.concat(1..3, 4..6)
iex> cycle = Stream.cycle([:a, :b, :c])
iex> Stream.zip(concat, cycle) |> Enum.to_list
[{1, :a}, {2, :b}, {3, :c}, {4, :a}, {5, :b}, {6, :c}]
"""
@spec zip(Enumerable.t, Enumerable.t) :: Enumerable.t
def zip(left, right) do
step = &do_zip_step(&1, &2)
left_fun = &Enumerable.reduce(left, &1, step)
right_fun = &Enumerable.reduce(right, &1, step)
# Return a function as a lazy enumerator.
&do_zip([{left_fun, []}, {right_fun, []}], &1, &2)
end
defp do_zip(zips, {:halt, acc}, _fun) do
do_zip_close(zips)
{:halted, acc}
end
defp do_zip(zips, {:suspend, acc}, fun) do
{:suspended, acc, &do_zip(zips, &1, fun)}
end
defp do_zip(zips, {:cont, acc}, callback) do
try do
do_zip(zips, acc, callback, [], [])
catch
kind, reason ->
stacktrace = System.stacktrace
do_zip_close(zips)
:erlang.raise(kind, reason, stacktrace)
else
{:next, buffer, acc} ->
do_zip(buffer, acc, callback)
{:done, _} = o ->
o
end
end
defp do_zip([{fun, fun_acc} | t], acc, callback, list, buffer) do
case fun.({:cont, fun_acc}) do
{:suspended, [i | fun_acc], fun} ->
do_zip(t, acc, callback, [i | list], [{fun, fun_acc} | buffer])
{_, _} ->
do_zip_close(:lists.reverse(buffer, t))
{:done, acc}
end
end
defp do_zip([], acc, callback, list, buffer) do
zipped = List.to_tuple(:lists.reverse(list))
{:next, :lists.reverse(buffer), callback.(zipped, acc)}
end
defp do_zip_close([]), do: :ok
defp do_zip_close([{fun, acc} | t]) do
fun.({:halt, acc})
do_zip_close(t)
end
defp do_zip_step(x, acc) do
{:suspend, [x | acc]}
end
## Sources
@doc """
Creates a stream that cycles through the given enumerable,
infinitely.
## Examples
iex> stream = Stream.cycle([1, 2, 3])
iex> Enum.take(stream, 5)
[1, 2, 3, 1, 2]
"""
@spec cycle(Enumerable.t) :: Enumerable.t
def cycle(enumerable)
def cycle(enumerable) when is_list(enumerable) do
unfold {enumerable, enumerable}, fn
{source, [h | t]} -> {h, {source, t}}
{source = [h | t], []} -> {h, {source, t}}
end
end
def cycle(enumerable) do
fn acc, fun ->
inner = &do_cycle_each(&1, &2, fun)
outer = &Enumerable.reduce(enumerable, &1, inner)
do_cycle(outer, outer, acc)
end
end
defp do_cycle(_reduce, _cycle, {:halt, acc}) do
{:halted, acc}
end
defp do_cycle(reduce, cycle, {:suspend, acc}) do
{:suspended, acc, &do_cycle(reduce, cycle, &1)}
end
defp do_cycle(reduce, cycle, acc) do
try do
reduce.(acc)
catch
{:stream_cycle, acc} ->
{:halted, acc}
else
{state, acc} when state in [:done, :halted] ->
do_cycle(cycle, cycle, {:cont, acc})
{:suspended, acc, continuation} ->
{:suspended, acc, &do_cycle(continuation, cycle, &1)}
end
end
defp do_cycle_each(x, acc, f) do
case f.(x, acc) do
{:halt, h} -> throw({:stream_cycle, h})
{_, _} = o -> o
end
end
@doc """
Emits a sequence of values, starting with `start_value`. Successive
values are generated by calling `next_fun` on the previous value.
## Examples
iex> Stream.iterate(0, &(&1+1)) |> Enum.take(5)
[0, 1, 2, 3, 4]
"""
@spec iterate(element, (element -> element)) :: Enumerable.t
def iterate(start_value, next_fun) do
unfold({:ok, start_value}, fn
{:ok, value} ->
{value, {:next, value}}
{:next, value} ->
next = next_fun.(value)
{next, {:next, next}}
end)
end
@doc """
Returns a stream generated by calling `generator_fun` repeatedly.
## Examples
# Although not necessary, let's seed the random algorithm
iex> :rand.seed(:exsplus, {1, 2, 3})
iex> Stream.repeatedly(&:rand.uniform/0) |> Enum.take(3)
[0.40502929729990744, 0.45336720247823126, 0.04094511692041057]
"""
@spec repeatedly((() -> element)) :: Enumerable.t
def repeatedly(generator_fun) when is_function(generator_fun, 0) do
&do_repeatedly(generator_fun, &1, &2)
end
defp do_repeatedly(generator_fun, {:suspend, acc}, fun) do
{:suspended, acc, &do_repeatedly(generator_fun, &1, fun)}
end
defp do_repeatedly(_generator_fun, {:halt, acc}, _fun) do
{:halted, acc}
end
defp do_repeatedly(generator_fun, {:cont, acc}, fun) do
do_repeatedly(generator_fun, fun.(generator_fun.(), acc), fun)
end
@doc """
Emits a sequence of values for the given resource.
Similar to `transform/3` but the initial accumulated value is
computed lazily via `start_fun` and executes an `after_fun` at
the end of enumeration (both in cases of success and failure).
Successive values are generated by calling `next_fun` with the
previous accumulator (the initial value being the result returned
by `start_fun`) and it must return a tuple containing a list
of items to be emitted and the next accumulator. The enumeration
finishes if it returns `{:halt, acc}`.
As the name says, this function is useful to stream values from
resources.
## Examples
Stream.resource(fn -> File.open!("sample") end,
fn file ->
case IO.read(file, :line) do
data when is_binary(data) -> {[data], file}
_ -> {:halt, file}
end
end,
fn file -> File.close(file) end)
"""
@spec resource((() -> acc), (acc -> {[element], acc} | {:halt, acc}), (acc -> term)) :: Enumerable.t
def resource(start_fun, next_fun, after_fun) do
&do_resource(start_fun.(), next_fun, &1, &2, after_fun)
end
defp do_resource(next_acc, next_fun, {:suspend, acc}, fun, after_fun) do
{:suspended, acc, &do_resource(next_acc, next_fun, &1, fun, after_fun)}
end
defp do_resource(next_acc, _next_fun, {:halt, acc}, _fun, after_fun) do
after_fun.(next_acc)
{:halted, acc}
end
defp do_resource(next_acc, next_fun, {:cont, acc}, fun, after_fun) do
try do
# Optimize the most common cases
case next_fun.(next_acc) do
{[], next_acc} -> {:opt, {:cont, acc}, next_acc}
{[v], next_acc} -> {:opt, fun.(v, acc), next_acc}
{_, _} = other -> other
end
catch
kind, reason ->
stacktrace = System.stacktrace
after_fun.(next_acc)
:erlang.raise(kind, reason, stacktrace)
else
{:opt, acc, next_acc} ->
do_resource(next_acc, next_fun, acc, fun, after_fun)
{:halt, next_acc} ->
do_resource(next_acc, next_fun, {:halt, acc}, fun, after_fun)
{list, next_acc} when is_list(list) ->
do_list_resource(next_acc, next_fun, {:cont, acc}, fun, after_fun,
&Enumerable.List.reduce(list, &1, fun))
{enum, next_acc} ->
inner = &do_resource_each(&1, &2, fun)
do_enum_resource(next_acc, next_fun, {:cont, acc}, fun, after_fun,
&Enumerable.reduce(enum, &1, inner))
end
end
defp do_list_resource(next_acc, next_fun, acc, fun, after_fun, reduce) do
try do
reduce.(acc)
catch
kind, reason ->
stacktrace = System.stacktrace
after_fun.(next_acc)
:erlang.raise(kind, reason, stacktrace)
else
{:done, acc} ->
do_resource(next_acc, next_fun, {:cont, acc}, fun, after_fun)
{:halted, acc} ->
do_resource(next_acc, next_fun, {:halt, acc}, fun, after_fun)
{:suspended, acc, c} ->
{:suspended, acc, &do_list_resource(next_acc, next_fun, &1, fun, after_fun, c)}
end
end
defp do_enum_resource(next_acc, next_fun, {op, acc}, fun, after_fun, reduce) do
try do
reduce.({op, [:outer | acc]})
catch
kind, reason ->
stacktrace = System.stacktrace
after_fun.(next_acc)
:erlang.raise(kind, reason, stacktrace)
else
{:halted, [:outer | acc]} ->
do_resource(next_acc, next_fun, {:cont, acc}, fun, after_fun)
{:halted, [:inner | acc]} ->
do_resource(next_acc, next_fun, {:halt, acc}, fun, after_fun)
{:done, [_ | acc]} ->
do_resource(next_acc, next_fun, {:cont, acc}, fun, after_fun)
{:suspended, [_ | acc], c} ->
{:suspended, acc, &do_enum_resource(next_acc, next_fun, &1, fun, after_fun, c)}
end
end
defp do_resource_each(x, [:outer | acc], f) do
case f.(x, acc) do
{:halt, res} -> {:halt, [:inner | res]}
{op, res} -> {op, [:outer | res]}
end
end
@doc """
Emits a sequence of values for the given accumulator.
Successive values are generated by calling `next_fun` with the previous
accumulator and it must return a tuple with the current value and next
accumulator. The enumeration finishes if it returns `nil`.
## Examples
iex> Stream.unfold(5, fn 0 -> nil; n -> {n, n-1} end) |> Enum.to_list()
[5, 4, 3, 2, 1]
"""
@spec unfold(acc, (acc -> {element, acc} | nil)) :: Enumerable.t
def unfold(next_acc, next_fun) do
&do_unfold(next_acc, next_fun, &1, &2)
end
defp do_unfold(next_acc, next_fun, {:suspend, acc}, fun) do
{:suspended, acc, &do_unfold(next_acc, next_fun, &1, fun)}
end
defp do_unfold(_next_acc, _next_fun, {:halt, acc}, _fun) do
{:halted, acc}
end
defp do_unfold(next_acc, next_fun, {:cont, acc}, fun) do
case next_fun.(next_acc) do
nil -> {:done, acc}
{v, next_acc} -> do_unfold(next_acc, next_fun, fun.(v, acc), fun)
end
end
## Helpers
@compile {:inline, lazy: 2, lazy: 3, lazy: 4}
defp lazy(%Stream{done: nil, funs: funs} = lazy, fun),
do: %{lazy | funs: [fun | funs] }
defp lazy(enum, fun),
do: %Stream{enum: enum, funs: [fun]}
defp lazy(%Stream{done: nil, funs: funs, accs: accs} = lazy, acc, fun),
do: %{lazy | funs: [fun | funs], accs: [acc | accs] }
defp lazy(enum, acc, fun),
do: %Stream{enum: enum, funs: [fun], accs: [acc]}
defp lazy(%Stream{done: nil, funs: funs, accs: accs} = lazy, acc, fun, done),
do: %{lazy | funs: [fun | funs], accs: [acc | accs], done: done}
defp lazy(enum, acc, fun, done),
do: %Stream{enum: enum, funs: [fun], accs: [acc], done: done}
end
defimpl Enumerable, for: Stream do
@compile :inline_list_funs
def reduce(lazy, acc, fun) do
do_reduce(lazy, acc, fn x, [acc] ->
{reason, acc} = fun.(x, acc)
{reason, [acc]}
end)
end
def count(_lazy) do
{:error, __MODULE__}
end
def member?(_lazy, _value) do
{:error, __MODULE__}
end
defp do_reduce(%Stream{enum: enum, funs: funs, accs: accs, done: done}, acc, fun) do
composed = :lists.foldl(fn fun, acc -> fun.(acc) end, fun, funs)
do_each(&Enumerable.reduce(enum, &1, composed),
done && {done, fun}, :lists.reverse(accs), acc)
end
defp do_each(reduce, done, accs, {command, acc}) do
case reduce.({command, [acc | accs]}) do
{:suspended, [acc | accs], continuation} ->
{:suspended, acc, &do_each(continuation, done, accs, &1)}
{:halted, accs} ->
do_done {:halted, accs}, done
{:done, accs} ->
do_done {:done, accs}, done
end
end
defp do_done({reason, [acc | _]}, nil), do: {reason, acc}
defp do_done({reason, [acc | t]}, {done, fun}) do
[h | _] = Enum.reverse(t)
case done.([acc, h], fun) do
{:cont, [acc | _]} -> {reason, acc}
{:halt, [acc | _]} -> {:halted, acc}
{:suspend, [acc | _]} -> {:suspended, acc, &({:done, elem(&1, 1)})}
end
end
end
defimpl Inspect, for: Stream do
import Inspect.Algebra
def inspect(%{enum: enum, funs: funs}, opts) do
inner = [enum: enum, funs: Enum.reverse(funs)]
concat ["#Stream<", to_doc(inner, opts), ">"]
end
end
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