# A lens for the key :name
Focus.Lens.make_lens(:name)

# A lens for the key "name"
Focus.Lens.make_lens("name")

# A lens for the second item in a list/tuple:
Focus.Lens.make_lens(1)

# Extract a value from a simple map:

person = %{name: "Homer"}
nameLens = Focus.Lens.make_lens(:name)

Focus.Lens.view!(nameLens, person) == "Homer"
# true

Focus.Lens.set(nameLens, person, "Bart")
# %{name: "Bart"}

Focus.Lens.over(nameLens, person, &String.upcase/1)
# %{name: "HOMER"}

person = %{
  name: "Homer",
  address: %{
    locale: %{
      number: 742,
      street: "Evergreen Terrace",
      city: "Springfield",
    },
    state: "???"
  }
}

# To access the street, we can compose the lenses that lead there from the top level.
# Lenses can be composed with Focus.Lens.compose/2, or the infix (~>) operator.

address = Focus.Lens.make_lens(:address)
locale =  Focus.Lens.make_lens(:locale)
street =  Focus.Lens.make_lens(:street)

address
~> locale
~> street
|> Focus.Lens.view!(person)
# "Evergreen Terrace"

address
~> locale
~> street
|> Focus.Lens.set(person, "Fake Street")
# person = %{
#   name: "Homer",
#   address: %{
#     locale: %{
#       number: 742,
#       street: "Fake Street",
#       city: "Springfield",
#     },
#     state: "???"
#   }
# }