View Source Witchcraft.Traversable (Witchcraft v1.0.6-doma)
Walk through a data structure from left to right, running some action on each element in turn.
Similar to applicatives, it can be used to do things like collecting some effect while performing other actions.
type-class
Type Class
An instance of Witchcraft.Traversable
must also implement Witchcraft.Foldable
and Witchcraft.Functor
, and define Witchcraft.Foldable.right_fold/3
.
[right_fold/3] Foldable Functor [map/2]
↓ ↓
Traversable
[right_fold/3]
Link to this section Summary
Functions
Run each action/effect in sequence (from left to right), and accumulate values along the way.
traverse/2
with arguments reversed.
Convert elements to actions, and then evaluate the actions from left-to-right, and accumulate the results.
Link to this section Types
@type t() :: any()
Link to this section Functions
@spec sequence(t()) :: Witchcraft.Foldable.t()
Run each action/effect in sequence (from left to right), and accumulate values along the way.
examples
Examples
iex> sequence([{1, 2, 3}, {4, 5, 6}])
{5, 7, [3, 6]}
iex> [
...> [1, 2, 3],
...> [4, 5, 6]
...> ]
...> |> sequence()
[
[1, 4],
[1, 5],
[1, 6],
[2, 4],
[2, 5],
[2, 6],
[3, 4],
[3, 5],
[3, 6]
]
traverse/2
with arguments reversed.
examples
Examples
iex> fn x -> {x, x * 2, x * 10} end |> through([1, 2, 3])
{6, 12, [10, 20, 30]}
iex> fn x -> [x] end |> through({1, 2, 3})
[{1, 2, 3}]
iex> fn x -> [x, x * 5, x * 10] end |> through({1, 2, 3})
[
{1, 2, 3},
{1, 2, 15},
{1, 2, 30}
]
iex> fn x -> [x, x * 5, x * 10] end |> through([1, 2, 3])
[
#
[1, 2, 3], [1, 2, 15], [1, 2, 30],
[1, 10, 3], [1, 10, 15], [1, 10, 30],
[1, 20, 3], [1, 20, 15], [1, 20, 30],
#
[5, 2, 3], [5, 2, 15], [5, 2, 30],
[5, 10, 3], [5, 10, 15], [5, 10, 30],
[5, 20, 3], [5, 20, 15], [5, 20, 30],
#
[10, 2, 3], [10, 2, 15], [10, 2, 30],
[10, 10, 3], [10, 10, 15], [10, 10, 30],
[10, 20, 3], [10, 20, 15], [10, 20, 30]
]
Convert elements to actions, and then evaluate the actions from left-to-right, and accumulate the results.
For a version without accumulation, see then_traverse/2
.
examples
Examples
iex> traverse([1, 2, 3], fn x -> {x, x * 2, x * 10} end)
{6, 12, [10, 20, 30]}
iex> traverse({1, 2, 3}, fn x -> [x] end)
[{1, 2, 3}]
iex> traverse({1, 2, 3}, fn x -> [x, x * 5, x * 10] end)
[
{1, 2, 3},
{1, 2, 15},
{1, 2, 30}
]
iex> traverse([1, 2, 3], fn x -> [x, x * 5, x * 10] end)
[
#
[1, 2, 3], [1, 2, 15], [1, 2, 30],
[1, 10, 3], [1, 10, 15], [1, 10, 30],
[1, 20, 3], [1, 20, 15], [1, 20, 30],
#
[5, 2, 3], [5, 2, 15], [5, 2, 30],
[5, 10, 3], [5, 10, 15], [5, 10, 30],
[5, 20, 3], [5, 20, 15], [5, 20, 30],
#
[10, 2, 3], [10, 2, 15], [10, 2, 30],
[10, 10, 3], [10, 10, 15], [10, 10, 30],
[10, 20, 3], [10, 20, 15], [10, 20, 30]
]
traverse([1, 2, 3], fn x -> %Algae.Maybe.Just{just: x} end)
#=> %Algae.Maybe.Just{just: [1, 2, 3]}
traverse(%Algae.Maybe.Just{just: 4}, fn x -> [x, x * 10] end)
#=> [
# %Algae.Maybe.Just{just: 4},
# %Algae.Maybe.Just{just: 40}
# ]
traverse([1, 2, 3], fn x ->
if is_even(x) do
%Algae.Maybe.Just{just: x}
else
%Algae.Maybe.Nothing{}
end
end)
#=> %Algae.Maybe.Nothing{}