MonadEx v1.1.3 Monad.Reader View Source

The reader monad is great for situations when you need to share some environment or state between several operations.

Reader monads are great for dependency injection. The environment is specified separately from the operations.

Example

iex> import Curry
iex> use Monad.Operators
iex> env = %{dev: %{url: "http://www.example.com/dev"}, prod: %{url: "https://www.example.com/prod"}}
iex> r = reader(& env[&1])
...> ~>> (& return(&1[:url]))
...> ~>> (& return(&1 <> "/index.html"))
iex> fun = runReader r
iex> fun.(:dev)
"http://www.example.com/dev/index.html"
iex> fun.(:prod)
"https://www.example.com/prod/index.html"

iex> reader = curry(& &1 + &2) <|> reader(& &1 * 2) <~> reader(& &1 * &1)
iex> fun = runReader reader
iex> fun.(2)
8
iex> fun.(-12)
120

Link to this section Summary

Types

t()

Functions

bind(reader, fun)

Callback implementation of Monad.Behaviour.bind/2

reader(fun)

Wraps fun in a reader monad

return(value)

Callback implementation of Monad.Behaviour.return/1

runReader(reader)

Unwraps the function from the reader

Link to this section Types

t() (opaque)

t()

Link to this section Functions

bind(reader, fun)

bind(t(), (term() -> t())) :: t()

Callback implementation of Monad.Behaviour.bind/2.

iex> r = reader &(&1 * 2)
iex> bind r, &(&1 + 3)
iex> f = runReader r
iex> f.(10)
20

reader(fun)

reader((term() -> term())) :: t()

Wraps fun in a reader monad.

iex> r = reader &(&1)
iex> r.fun.(4)
4

return(value)

return(term()) :: t()

Callback implementation of Monad.Behaviour.return/1.

Converts value into a function that always returns value. Then wraps that function into a reader monad.

iex> r = return 42
iex> r.fun.(:unused)
42

runReader(reader)

runReader(t()) :: (term() -> term())

Unwraps the function from the reader.

iex> r = reader &(&1 * 2) iex> f = runReader r iex> f.(3) 6