Algae.Reader (Algae v1.3.1) View Source
Algae.Reader allows you to pass some readable context around through actions.
This is useful in a number of situations, but the most common case is to weave access to environment variables monadically.
For an illustrated guide to Readers,
see Thee Useful Monads.
Examples
iex> use Witchcraft
...>
iex> correct =
...> monad %Algae.Reader{} do
...> count <- ask &Map.get(&1, :count)
...> bindings <- ask()
...> return (count == map_size(bindings))
...> end
...>
iex> sample_bindings = %{count: 3, a: 1, b: 2}
iex> correct_count = run(correct, sample_bindings)
iex> "Correct count for #{inspect sample_bindings}? #{correct_count}"
"Correct count for %{a: 1, b: 2, count: 3}? true"
...>
iex> bad_bindings = %{count: 100, a: 1, b: 2}
iex> bad_count = run(correct, bad_bindings)
iex> "Correct count for #{inspect bad_bindings}? #{bad_count}"
"Correct count for %{a: 1, b: 2, count: 100}? false"Example adapted from source
Link to this section Summary
Functions
Get the wrapped environment. Especially useful in monadic do-notation.
Similar to new/1 and ask/0. Construct an Algae.Reader,
but apply a function to the constructed envoronment.
Locally composes a function into a Reader.
Default Elixir.Algae.Reader struct
Reader constructor.
Run the reader function with some argument.
Link to this section Types
Specs
t() :: %Algae.Reader{reader: (... -> any())}
Link to this section Functions
Specs
ask() :: t()
Get the wrapped environment. Especially useful in monadic do-notation.
Examples
iex> run(ask(), 42)
42
iex> use Witchcraft
...>
...> example_fun =
...> fn x ->
...> monad %Algae.Reader{} do
...> e <- ask()
...> return {x, e}
...> end
...> end
...>
...> 42
...> |> example_fun.()
...> |> run(7)
{42, 7}Specs
Similar to new/1 and ask/0. Construct an Algae.Reader,
but apply a function to the constructed envoronment.
The pun here is that you're "asking" a function for something.
Examples
iex> fn x -> x * 10 end
...> |> ask()
...> |> run(5)
50
iex> use Witchcraft
...>
...> foo =
...> fn words ->
...> monad %Algae.Reader{} do
...> loud <- ask &(&1 == String.upcase(&1))
...> return(words <> (if loud, do: "!", else: "."))
...> end
...> end
...>
...> "Hello" |> foo.() |> run("WORLD") # "WORLD" is the context being asked for
"Hello!"Specs
Locally composes a function into a Reader.
Often the idea is to temporarily adapt the Reader without continuing this
change in later runs.
Examples
iex> ask()
...> |> local(fn word -> word <> "!" end)
...> |> local(&String.upcase/1)
...> |> run("o hai thar")
"O HAI THAR!"Specs
new() :: t()
Default Elixir.Algae.Reader struct
Specs
Reader constructor.
Examples
iex> newbie = new(fn x -> x * 10 end)
...> newbie.reader.(10)
100Specs
Run the reader function with some argument.
iex> reader = new(fn x -> x + 5 end)
...> run(reader, 42)
47This is the opposite of new/1.
iex> fun = fn x -> x + 5 end
...> fun.(42) == fun |> new() |> run(42)
true