Algae provides a boilerplate-avoiding DSL for defining algebraic data types (ADTs), plus several common structures
Quickstart
Add Algae to your list of dependencies in mix.exs
:
def deps do
[{:algae, "~> 1.2"}]
end
Table of Contents
NOTE
Pleaseimport Algae
before trying out the examples below. The samples assume that is has already been done to remove the unnecessary clutter.
Product Builder
Build a product type
Includes:
- Struct
- Type definition
- Constructor function (for piping and defaults)
- Implicit defaults for simple values
Definition DSL
For convenience, several variants of the DSL are available.
Standard
defmodule Player do
# =============== #
# Data Definition #
# =============== #
defdata do
name :: String.t()
hit_points :: non_neg_integer()
experience :: non_neg_integer()
end
# =================== #
# Rest of Module #
# (business as usual) #
# =================== #
@spec attack(t(), t()) :: {t(), t()}
def attack(%{experience: xp} = player, %{hit_points: hp} = target) do
{
%{player | experience: xp + 50},
%{target | hit_points: hp - 10}
}
end
end
#=> %Player{name: "Sir Bob", hit_points: 10, experience: 500}
Single Field Shorthand
Without any fields specified, Algae will default to a single field with the same name as the module (essentially a "wrapper type"). You must still provide the type for this field, however.
Embedded in another module:
defmodule Id do
defdata any()
end
%Id{}
#=> %Id{id: nil}
Standalone:
defdata Wrapper :: any()
%Wrapper{}
#=> %Wrapper{wrapper: nil}
Constructor
A helper function, especially useful for piping. The order of arguments is the same as the order that they are defined in.
defmodule Person do
defdata do
name :: String.t()
age :: non_neg_integer()
end
end
Person.new("Rachel Weintraub")
#=> %Person{
# name: "Rachel Weintraub",
# age: 0
# }
Constructor Defaults
Fields will automatically default to a sensible value (a typical "zero" for
that datatype). For example, non_neg_integer()
will default to 0
,
and String.t()
will default to ""
.
You may also overwrite these defaults with the \\
syntax.
defmodule Pet do
defdata do
name :: String.t()
leg_count :: non_neg_integer() \\ 4
end
end
Pet.new("Crookshanks")
#=> %Pet{
# name: "Crookshanks",
# leg_count: 4
# }
Pet.new("Paul the Psychic Octopus", 8)
#=> %Pet{
# name: "Paul the Psychic Octopus",
# leg_count: 8
# }
This overwriting syntax is required for complex types:
defdata Grocery do
item :: {String.t(), integer(), boolean()} \\ {"Orange", 4, false}
end
Grocery.new()
#=> %Grocery{
# item: {"Orange", 4, false}
# }
Overwrite Constructor
The new
constructor function may be overwritten.
defmodule Constant do
defdata :: fun()
def new(value), do: %Constant{constant: fn _ -> value end}
end
fourty_two = Constant.new(42)
fourty_two.constant.(33)
#=> 42
Empty Tag
An empty type (with no fields) is definable using the none
() type
defmodule Nothing do
defdata none()
end
Nothing.new()
#=> %Nothing{}
Sum Builder
Build a sum (coproduct) type from product types
defmodule Light do
# ============== #
# Sum Definition #
# ============== #
defsum do
defdata Red :: none()
defdata Yellow :: none()
defdata Green :: none()
end
# =================== #
# Rest of Module #
# (business as usual) #
# =================== #
def from_number(1), do: %Light.Red{}
def from_number(2), do: %Light.Yellow{}
def from_number(3), do: %Light.Green{}
end
Light.new()
#=> %Light.Red{}
Embedded Products
Data with multiple fields can be defined directly as part of a sum
defmodule Pet do
defsum do
defdata Cat do
name :: String.t()
claw_sharpness :: String.t()
end
defdata Dog do
name :: String.t()
bark_loudness :: non_neg_integer()
end
end
end
Default Constructor
The first defdata
's constructor will be the default constructor for the sum
defmodule Maybe do
defsum do
defdata Nothing :: none()
defdata Just :: any()
end
end
Maybe.new()
#=> %Maybe.Nothing{}
Tagged Unions
Sums join existing types with tags: new types to help distinguish the context that they are in (the sum type)
defdata Book :: String.t() \\ "War and Peace"
defdata Video :: String.t() \\ "2001: A Space Odyssey"
defmodule Media do
defsum do
defdata Paper :: Book.t()
defdata Film :: Video.t() \\ Video.new("A Clockwork Orange")
end
end
media = Media.new()
#=> %Paper{
# paper: %Book{
# book: "War and Peace"
# }
# }
A Sampling of ADTs
See complete docs for more
Algae.Id
The simplest ADT: a simple wrapper for some data
%Algae.Id{id: "hi!"}
Algae.Maybe
Maybe represents the presence or absence of something.
Please note that nil
is actually a value, as it can be passed to functions!
nil
is not bottom!
Algae.Maybe.new()
#=> %Algae.Maybe.Nothing{}
Algae.Maybe.new(42)
#=> %Algae.Maybe.Just{just: 42}
Tree.BinarySearch
alias Algae.Tree.BinarySearch, as: BTree
# 42
# / \
# 77 1234
# / \
# 98 32
BTree.Branch.new(
42,
BTree.Branch.new(77),
BTree.Branch.new(
1234,
BTree.Branch.new(98),
BTree.Branch.new(32)
)
)
#=> %Algae.Tree.BinarySearch.Branch{
# value: 42,
# left: %Algae.Tree.BinarySearch.Branch{
# value: 77,
# left: %Algae.Tree.BinarySearch.Empty{},
# right: %Algae.Tree.BinarySearch.Empty{}
# },
# right: %Algae.Tree.BinarySearch.Branch{
# value: 1234,
# left: %Algae.Tree.BinarySearch.Branch{
# value: 98,
# left: %Algae.Tree.BinarySearch.Empty{},
# right: %Algae.Tree.BinarySearch.Empty{}
# },
# right: %Algae.Tree.BinarySearch.Branch{
# value: 32,
# left: %Algae.Tree.BinarySearch.Empty{},
# right: %Algae.Tree.BinarySearch.Empty{}
# }
# }
# }