Prism (focus v0.4.0)

Prisms are like lenses, but used when the view focused on may not exist.

This includes sum types; although not backed by an explicit Maybe type, the [{:ok, any} | {:error}] convention is explicitly supported as a value that a prism can focus on.

Link to this section Summary

Types

t()

Functions

error()

A prism that matches an {:error, } tuple. Note that on a successful match, view/set/over will return {:ok, }

ok()

A prism that matches an {:ok, _} tuple.

Link to this section Types

t()

Specs

t() :: %Prism{get: (any() -> any()), put: ((any() -> any()) -> any())}

Link to this section Functions

error()

Specs

error() :: t()

A prism that matches an {:error, } tuple. Note that on a successful match, view/set/over will return {:ok, }

Examples

iex> error = Prism.error
iex> error |> Focus.view({:error, 5})
{:ok, 5}
iex> error |> Focus.set({:error, 5}, "Banana")
{:ok, "Banana"}
iex> error |> Focus.view({:ok, :oops})
{:error, {:prism, :bad_path}}

ok()

Specs

ok() :: t()

A prism that matches an {:ok, _} tuple.

Examples

iex> ok = Prism.ok
iex> ok |> Focus.view({:ok, 5})
{:ok, 5}
iex> ok |> Focus.set({:ok, 5}, "Banana")
{:ok, "Banana"}
iex> ok |> Focus.view({:error, :oops})
{:error, {:prism, :bad_path}}