/
stream.ex
1585 lines (1236 loc) · 46.1 KB
/
stream.ex
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defmodule Stream do
@moduledoc """
Functions for creating and composing streams.
Streams are composable, lazy enumerables (for an introduction on
enumerables, see the `Enum` module). 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 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(fun, entry, acc) do
quote(do: unquote(fun).(unquote(entry), unquote(acc)))
end
defmacrop acc(head, state, tail) do
quote(do: [unquote(head), unquote(state) | unquote(tail)])
end
defmacrop next_with_acc(fun, entry, head, state, tail) do
quote do
{reason, [head | tail]} = unquote(fun).(unquote(entry), [unquote(head) | unquote(tail)])
{reason, [head, unquote(state) | tail]}
end
end
## Transformers
# TODO: Remove by 2.0
@doc false
@deprecated "Use Stream.chunk_every/2 instead"
def chunk(enum, n), do: chunk(enum, n, n, nil)
# TODO: Remove by 2.0
@doc false
@deprecated "Use Stream.chunk_every/3 instead"
def chunk(enum, n, step) do
chunk_every(enum, n, step, nil)
end
# TODO: Remove by 2.0
@doc false
@deprecated "Use Stream.chunk_every/4 instead"
def chunk(enum, n, step, leftover)
when is_integer(n) and n > 0 and is_integer(step) and step > 0 do
chunk_every(enum, n, step, leftover || :discard)
end
@doc """
Shortcut to `chunk_every(enum, count, count)`.
"""
@doc since: "1.5.0"
@spec chunk_every(Enumerable.t(), pos_integer) :: Enumerable.t()
def chunk_every(enum, count), do: chunk_every(enum, count, count, [])
@doc """
Streams the enumerable in chunks, containing `count` items each,
where each new chunk starts `step` elements into the enumerable.
`step` is optional and, if not passed, defaults to `count`, i.e.
chunks do not overlap.
If the last chunk does not have `count` elements to fill the chunk,
elements are taken from `leftover` to fill in the chunk. If `leftover`
does not have enough elements to fill the chunk, then a partial chunk
is returned with less than `count` elements.
If `:discard` is given in `leftover`, the last chunk is discarded
unless it has exactly `count` elements.
## Examples
iex> Stream.chunk_every([1, 2, 3, 4, 5, 6], 2) |> Enum.to_list()
[[1, 2], [3, 4], [5, 6]]
iex> Stream.chunk_every([1, 2, 3, 4, 5, 6], 3, 2, :discard) |> Enum.to_list()
[[1, 2, 3], [3, 4, 5]]
iex> Stream.chunk_every([1, 2, 3, 4, 5, 6], 3, 2, [7]) |> Enum.to_list()
[[1, 2, 3], [3, 4, 5], [5, 6, 7]]
iex> Stream.chunk_every([1, 2, 3, 4, 5, 6], 3, 3, []) |> Enum.to_list()
[[1, 2, 3], [4, 5, 6]]
"""
@doc since: "1.5.0"
@spec chunk_every(Enumerable.t(), pos_integer, pos_integer, Enumerable.t() | :discard) ::
Enumerable.t()
def chunk_every(enum, count, step, leftover \\ [])
when is_integer(count) and count > 0 and is_integer(step) and step > 0 do
R.chunk_every(&chunk_while/4, enum, count, step, leftover)
end
@doc """
Chunks the `enum` by buffering elements for which `fun` returns the same value.
Elements are only emitted 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
R.chunk_by(&chunk_while/4, enum, fun)
end
@doc """
Chunks the `enum` with fine grained control when every chunk is emitted.
`chunk_fun` receives the current element and the accumulator and
must return `{:cont, element, acc}` to emit the given chunk and
continue with accumulator or `{:cont, acc}` to not emit any chunk
and continue with the return accumulator.
`after_fun` is invoked when iteration is done and must also return
`{:cont, element, acc}` or `{:cont, acc}`.
## Examples
iex> chunk_fun = fn item, acc ->
...> if rem(item, 2) == 0 do
...> {:cont, Enum.reverse([item | acc]), []}
...> else
...> {:cont, [item | acc]}
...> end
...> end
iex> after_fun = fn
...> [] -> {:cont, []}
...> acc -> {:cont, Enum.reverse(acc), []}
...> end
iex> stream = Stream.chunk_while(1..10, [], chunk_fun, after_fun)
iex> Enum.to_list(stream)
[[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]
"""
@doc since: "1.5.0"
@spec chunk_while(
Enumerable.t(),
acc,
(element, acc -> {:cont, chunk, acc} | {:cont, acc} | {:halt, acc}),
(acc -> {:cont, chunk, acc} | {:cont, acc})
) :: Enumerable.t()
when chunk: any
def chunk_while(enum, acc, chunk_fun, after_fun) do
lazy(
enum,
[acc | after_fun],
fn f1 -> chunk_while_fun(chunk_fun, f1) end,
&after_chunk_while/2
)
end
defp chunk_while_fun(callback, fun) do
fn entry, acc(head, [acc | after_fun], tail) ->
case callback.(entry, acc) do
{:cont, emit, acc} ->
# If we emit an item and then we have to halt,
# we need to disable the after_fun callback to
# avoid emitting even more items.
case next(fun, emit, [head | tail]) do
{:halt, [head | tail]} -> {:halt, acc(head, [acc | &{:cont, &1}], tail)}
{command, [head | tail]} -> {command, acc(head, [acc | after_fun], tail)}
end
{:cont, acc} ->
skip(acc(head, [acc | after_fun], tail))
{:halt, acc} ->
{:halt, acc(head, [acc | after_fun], tail)}
end
end
end
defp after_chunk_while(acc(h, [acc | after_fun], t), f1) do
case after_fun.(acc) do
{:cont, emit, acc} -> next_with_acc(f1, emit, h, [acc | after_fun], t)
{:cont, acc} -> {:cont, acc(h, [acc | after_fun], t)}
end
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 `===/2`.
## 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) 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 is_integer(n) and n >= 0 do
lazy(enum, n, fn f1 -> R.drop(f1) end)
end
def drop(enum, n) when is_integer(n) and 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.
## 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, nth)
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 a truthy value.
## 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 """
Maps the given `fun` over `enumerable` and flattens the result.
This function returns a new stream built by appending the result of invoking `fun`
on each element of `enumerable` together.
## 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 false
# TODO: Remove on 2.0
@deprecated "Use Stream.filter/2 + Stream.map/2 instead"
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.
Do not use this function to generate a sequence of numbers.
If blocking the caller process is not necessary, use
`Stream.iterate(0, & &1 + 1)` instead.
## 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 ->
Process.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 ->
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 apply the given function on
every `nth` item from the enumerable.
The first item is always passed to the given function.
`nth` must be a non-negative integer.
## Examples
iex> stream = Stream.map_every(1..10, 2, fn x -> x * 2 end)
iex> Enum.to_list(stream)
[2, 2, 6, 4, 10, 6, 14, 8, 18, 10]
iex> stream = Stream.map_every([1, 2, 3, 4, 5], 1, fn x -> x * 2 end)
iex> Enum.to_list(stream)
[2, 4, 6, 8, 10]
iex> stream = Stream.map_every(1..5, 0, fn x -> x * 2 end)
iex> Enum.to_list(stream)
[1, 2, 3, 4, 5]
"""
@doc since: "1.4.0"
@spec map_every(Enumerable.t(), non_neg_integer, (element -> any)) :: Enumerable.t()
def map_every(enum, nth, fun)
def map_every(enum, 1, fun), do: map(enum, fun)
def map_every(enum, 0, _fun), do: %Stream{enum: enum}
def map_every([], _nth, _fun), do: %Stream{enum: []}
def map_every(enum, nth, fun) when is_integer(nth) and nth > 0 do
lazy(enum, nth, fn f1 -> R.map_every(nth, 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:
File.stream!("/path/to/file")
|> Stream.map(&String.replace(&1, "#", "%"))
|> Stream.into(File.stream!("/path/to/other/file"))
|> Stream.run()
No computation will be done until we call one of the `Enum` functions
or `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. Uses the first element in the enumerable
as the starting value.
## 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.scan2(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.scan3(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.
## 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, nth)
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 a truthy value.
## 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) 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) 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)
funs = {user, fun, inner, after_fun}
do_transform(user_acc.(), :cont, next, inner_acc, funs)
end
defp do_transform(user_acc, _next_op, next, {:halt, inner_acc}, funs) do
{_, _, _, after_fun} = funs
next.({:halt, []})
do_after(after_fun, user_acc)
{:halted, inner_acc}
end
defp do_transform(user_acc, next_op, next, {:suspend, inner_acc}, funs) do
{:suspended, inner_acc, &do_transform(user_acc, next_op, next, &1, funs)}
end
defp do_transform(user_acc, :halt, _next, {_, inner_acc}, funs) do
{_, _, _, after_fun} = funs
do_after(after_fun, user_acc)
{:halted, inner_acc}
end
defp do_transform(user_acc, :cont, next, inner_acc, funs) do
{_, _, _, after_fun} = funs
try do
next.({:cont, []})
catch
kind, reason ->
do_after(after_fun, user_acc)
:erlang.raise(kind, reason, __STACKTRACE__)
else
{:suspended, vals, next} ->
do_transform_user(:lists.reverse(vals), user_acc, :cont, next, inner_acc, funs)
{_, vals} ->
do_transform_user(:lists.reverse(vals), user_acc, :halt, next, inner_acc, funs)
end
end
defp do_transform_user([], user_acc, next_op, next, inner_acc, funs) do
do_transform(user_acc, next_op, next, inner_acc, funs)
end
defp do_transform_user([val | vals], user_acc, next_op, next, inner_acc, funs) do
{user, fun, inner, after_fun} = funs
try do
user.(val, user_acc)
catch
kind, reason ->
next.({:halt, []})
do_after(after_fun, user_acc)
:erlang.raise(kind, reason, __STACKTRACE__)
else
{[], user_acc} ->
do_transform_user(vals, user_acc, next_op, next, inner_acc, funs)
{list, user_acc} when is_list(list) ->
reduce = &Enumerable.List.reduce(list, &1, fun)
do_list_transform(vals, user_acc, next_op, next, inner_acc, reduce, funs)
{:halt, user_acc} ->
next.({:halt, []})
do_after(after_fun, user_acc)
{:halted, elem(inner_acc, 1)}
{other, user_acc} ->
reduce = &Enumerable.reduce(other, &1, inner)
do_enum_transform(vals, user_acc, next_op, next, inner_acc, reduce, funs)
end
end
defp do_list_transform(vals, user_acc, next_op, next, inner_acc, reduce, funs) do
{_, _, _, after_fun} = funs
try do
reduce.(inner_acc)
catch
kind, reason ->
next.({:halt, []})
do_after(after_fun, user_acc)
:erlang.raise(kind, reason, __STACKTRACE__)
else
{:done, acc} ->
do_transform_user(vals, user_acc, next_op, next, {:cont, acc}, funs)
{:halted, acc} ->
next.({:halt, []})
do_after(after_fun, user_acc)
{:halted, acc}
{:suspended, acc, continuation} ->
resume = &do_list_transform(vals, user_acc, next_op, next, &1, continuation, funs)
{:suspended, acc, resume}
end
end
defp do_enum_transform(vals, user_acc, next_op, next, {op, inner_acc}, reduce, funs) do
{_, _, _, after_fun} = funs
try do
reduce.({op, [:outer | inner_acc]})
catch
kind, reason ->
next.({:halt, []})
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(vals, user_acc, next_op, next, {:cont, acc}, funs)
{:halted, [_ | acc]} ->
next.({:halt, []})
do_after(after_fun, user_acc)
{:halted, acc}
{:done, [_ | acc]} ->
do_transform_user(vals, user_acc, next_op, next, {:cont, acc}, funs)
{:suspended, [_ | acc], continuation} ->
resume = &do_enum_transform(vals, user_acc, next_op, next, &1, continuation, funs)
{:suspended, acc, resume}
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
# TODO: Remove on 2.0
@deprecated "Use Stream.uniq_by/2 instead"
def uniq(enum, fun) do
uniq_by(enum, fun)
end
@doc """
Creates a stream that only emits elements if they are unique, by removing the