thunk v0.3.1 Thunk View Source

Laziness in Elixir. Thunks are computations that have not yet happened. This module provides the thunk type and functions for manipulating and creating thunks.

Thunks allow for setting up a computation and transforming it without evaluating it. A thunk can be used by other thunks and evaluation is shared.

Example

defmodule Infinity do
  require Thunk  

  @doc """
  An infinite list that just repeats its argument.

  ## Example

      iex> xs = Infinity.repeatedly(1)
      #Thunk<...>
      iex> [h | t] = Thunk.force(xs)
      [1 | #Thunk<...>]
  """
  def repeatedly(x) do
    Thunk.suspend([x | repeatedly(x)])
  end
end

Link to this section Summary

Types

element()

Alias for any

t()

Thunk type

Functions

apply(thunk_f, thunk_x)

Given a thunk with a function and a thunk with it’s argument, returns a thunk with the result of their application

copy(thunk)

Copies a thunk. When a thunk is forced it ceases to exist, so this function is useful for holding onto a result should it be forced

delete(thunk)

Deletes a thunk, to be used if the thunk does not need to ever be evaluated

exists?(thunk)

Is thunk still around?

force(thunk)

Forces a thunk. Raises a ThunkError if already forced or deleted

map(thunk, f)

Applies a function to a thunk

suspend(x)

Suspends a value in a thunk. Doesn’t evaluate it’s argument. Can be used as a do block as well

thunk?(arg1)

Is value a thunk?

Link to this section Types

element()

element() :: any()

Alias for any.

t() (opaque)

t()

Thunk type.

Link to this section Functions

apply(thunk_f, thunk_x)

apply(t(), t()) :: t()

Given a thunk with a function and a thunk with it’s argument, returns a thunk with the result of their application.

Example

iex> defmodule ThunkyMath do
...>   require Thunk   
...>
...>   # Add two thunks
...>   def add(x, y) do
...>    addr = fn n1 -> fn n2 -> n1 + n2 end end
...>     Thunk.map(x, addr)
...>     |> Thunk.apply(y)
...>   end
...> end
iex> x = Thunk.suspend(12)
iex> y = Thunk.suspend(13)
iex> z = ThunkyMath.add(x, y)
#Thunk<...>
iex> Thunk.force(z)
25

copy(thunk)

copy(t()) :: t()

Copies a thunk. When a thunk is forced it ceases to exist, so this function is useful for holding onto a result should it be forced.

Example

iex> thunk = Thunk.suspend(:some_computation)
iex> thunk_copy = Thunk.copy(thunk)
iex> Thunk.force(thunk)
iex> Thunk.exists?(thunk)
false
iex> Thunk.force(thunk_copy)
:some_computation

delete(thunk)

delete(t()) :: true

Deletes a thunk, to be used if the thunk does not need to ever be evaluated.

Example

iex> thunk = Thunk.suspend(:some_computation)
iex> Thunk.delete(thunk)
iex> Thunk.exists?(thunk)
false

exists?(thunk)

exists?(t()) :: boolean()

Is thunk still around?

force(thunk)

force(t()) :: any()

Forces a thunk. Raises a ThunkError if already forced or deleted.

Example

iex> thunk = Thunk.suspend(:value)
iex> Thunk.force(thunk)
:value

map(thunk, f)

map(t(), (element() -> any())) :: t()

Applies a function to a thunk.

Example

iex> thunk_x = Thunk.suspend(1)
iex> thunk_y = Thunk.map(thunk_x, fn x -> x + 1 end)
iex> Thunk.force(thunk_y)
2

suspend(x) (macro)

suspend(any()) :: t()

Suspends a value in a thunk. Doesn’t evaluate it’s argument. Can be used as a do block as well.

Example

iex> Thunk.suspend(raise("Oops you evaluated me!"))
#Thunk<...>
iex> Thunk.suspend do
...>   x = 5
...>   y = 6
...>   x + y
...> end
#Thunk<...>

thunk?(arg1)

thunk?(any()) :: boolean()

Is value a thunk?