mudasobwa
LazyFor → `Kernel.SpecialForms.for/1` but returning stream
The stream-based implementation of Kernel.SpecialForms.for/1. Allows the same syntax as for and acts the same way. This is an initial release. It does not yet support :into , :uniq, and :reduce options and bitstring comprehensions.
Everything else is supported.
Examples:
iex> import LazyFor
iex> # A list generator:
iex> result = stream n <- [1, 2, 3, 4], do: n * 2
iex> Enum.to_list(result)
[2, 4, 6, 8]
iex> # A comprehension with two generators
iex> result = stream x <- [1, 2], y <- [2, 3], do: x * y
iex> Enum.to_list(result)
[2, 3, 4, 6]
iex> # A comprehension with a generator and a filter
iex> result = stream n <- [1, 2, 3, 4, 5, 6], rem(n, 2) == 0, do: n
iex> Enum.to_list(result)
[2, 4, 6]
iex> users = [user: "john", admin: "meg", guest: "barbara"]
iex> result = stream {type, name} when type != :guest <- users do
...> String.upcase(name)
...> end
iex> Enum.to_list(result)
["JOHN", "MEG"]
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mudasobwa
Slightly moving forward. Simple binary comprehension and options (all but :reduce) do work.
iex|1 ▶ Enum.to_list(stream <<x <- "abcabca">>, do: x)
'abcabca'
iex|2 ▶ Enum.to_list(stream <<x <- "abcabca">>, uniq: true, do: x)
'abc'
iex|3 ▶ stream <<x <- "abcabca">>, take: 2, do: x
'ab'
Also :into works as a side effect (as described here)
I am not sure I am into implementing full bitstring support, but :reduce will come soon.
mudasobwa
Well, the latest hot discussion about semi-mutable not actually mutable syntactic sugar reminded me of my tech debt and I implemented reduce:.
test "binary for comprehensions with reduce, generators and filters" do
bin = "abc"
acc =
stream <<x <- bin>>, Integer.is_odd(x), <<y <- "hello">>, reduce: %{} do
inner_acc -> Map.update(inner_acc, x, [y], &[y | &1])
end
assert acc == %{97 => ~c"olleh", 99 => ~c"olleh"}
end
Under the hood, the slightly modified inner clause is applied to terminate the stream. Enjoy.
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