@spec ask() :: Funx.Monad.Effect.Right.t()

Returns a Funx.Monad.Effect.Right that yields the environment passed to Funx.Monad.Effect.run/2.

This is the Reader-style ask, used to access the full environment inside an effectful computation.

Example

iex> Funx.Monad.Effect.ask()
...> |> Funx.Monad.map(& &1[:region])
...> |> Funx.Monad.Effect.run(%{region: "us-west"})
%Funx.Monad.Either.Right{right: "us-west"}

@spec asks((term() -> term())) :: Funx.Monad.Effect.Right.t()

Returns a Funx.Monad.Effect.Right that applies the given function to the environment passed to Funx.Monad.Effect.run/2.

This allows extracting a value from the environment and using it in an effectful computation, following the Reader pattern.

Example

iex> Funx.Monad.Effect.asks(fn env -> env[:user] end)
...> |> Funx.Monad.bind(fn user -> Funx.Monad.Effect.right(user) end)
...> |> Funx.Monad.Effect.run(%{user: "alice"})
%Funx.Monad.Either.Right{right: "alice"}

@spec fail() :: Funx.Monad.Effect.Left.t()

Returns a Funx.Monad.Effect.Left that fails with the entire environment passed to Funx.Monad.Effect.run/2.

This is the Reader-style equivalent of ask/0, but marks the environment as a failure. Useful when the presence of certain runtime data should short-circuit execution.

Example

iex> Funx.Monad.Effect.fail()
...> |> Funx.Monad.Effect.run(%{error: :invalid_token})
%Funx.Monad.Either.Left{left: %{error: :invalid_token}}

@spec fails((term() -> term())) :: Funx.Monad.Effect.Left.t()

Returns a Funx.Monad.Effect.Left that applies the given function to the environment passed to Funx.Monad.Effect.run/2.

This is the failure-side equivalent of asks/1, used to produce an error effect based on runtime context.

Example

iex> Funx.Monad.Effect.fails(fn env -> {:missing_key, env} end)
...> |> Funx.Monad.Effect.run(%{input: nil})
%Funx.Monad.Either.Left{left: {:missing_key, %{input: nil}}}

@spec flip_either(t(error, value)) :: t(value, error)
when error: term(), value: term()

Inverts the success and failure branches of an Effect.

For a Right, this reverses the result: a successful value becomes a failure, and a failure becomes a success. For a Left, only failure is expected; if the Left produces a success, it is ignored.

This is useful when you want to reverse the semantics of a computation—treating an expected error as success, or vice versa.

Examples

iex> effect = Funx.Monad.Effect.pure(42)
iex> flipped = Funx.Monad.Effect.flip_either(effect)
iex> Funx.Monad.Effect.run(flipped)
%Funx.Monad.Either.Left{left: 42}
iex> effect = Funx.Monad.Effect.left("fail")
iex> flipped = Funx.Monad.Effect.flip_either(effect)
iex> Funx.Monad.Effect.run(flipped)
%Funx.Monad.Either.Right{right: "fail"}

@spec from_result(
  {:ok, right} | {:error, left},
  Funx.Monad.Effect.Context.opts_or_context()
) ::
  t(left, right)
when left: term(), right: term()

Converts an Elixir {:ok, value} or {:error, reason} tuple into an Effect.

Accepts an optional context context which includes telemetry tracking.

Examples

iex> result = Funx.Monad.Effect.from_result({:ok, 42})
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> result = Funx.Monad.Effect.from_result({:error, "error"})
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "error"}

@spec from_try((-> right), Funx.Monad.Effect.Context.opts_or_context()) ::
  t(Exception.t(), right)
when right: term()

Wraps a function in an Effect, catching exceptions and wrapping them in a Left.

You can optionally provide a Effect.Context for telemetry and span propagation.

Examples

iex> result = Funx.Monad.Effect.from_try(fn -> 42 end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> result = Funx.Monad.Effect.from_try(fn -> raise "error" end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: %RuntimeError{message: "error"}}

@spec left(left, Funx.Monad.Effect.Context.opts_or_context()) :: t(left, term())
when left: term()

Wraps a value in the Left variant of the Effect monad, representing a failed asynchronous computation.

Accepts either a keyword list of context options or a Effect.Context struct.

Examples

iex> result = Funx.Monad.Effect.left("error")
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "error"}

iex> context = Funx.Monad.Effect.Context.new(trace_id: "err-id", span_name: "failure")
iex> result = Funx.Monad.Effect.left("error", context)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "error"}

@spec lift_either(
  (-> Funx.Monad.Either.t(left, right)),
  Funx.Monad.Effect.Context.opts_or_context()
) ::
  t(left, right)
when left: term(), right: term()

Lifts a thunk that returns an Either into the Effect monad.

Instead of passing an Either value directly, you provide a zero-arity function (thunk) that returns one. This defers execution until the effect is run, allowing integration with tracing and composable pipelines.

You may also pass a context or options (opts) to configure telemetry or span metadata.

If the thunk raises an exception, it is caught and returned as a Left containing an EffectError tagged with :lift.

Examples

iex> result = Funx.Monad.Effect.lift_either(fn -> %Funx.Monad.Either.Right{right: 42} end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> result = Funx.Monad.Effect.lift_either(fn -> %Funx.Monad.Either.Left{left: "error"} end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "error"}

@spec lift_func((-> right), Funx.Monad.Effect.Context.opts_or_context()) ::
  t(left, right)
when left: term(), right: term()

Lifts a thunk into the Effect monad, wrapping its result in a Right.

This function defers execution of the given zero-arity function (thunk) until the effect is run. The result is automatically wrapped as Either.Right.

You may also pass a context or options (opts) to configure telemetry or span metadata.

If the thunk raises an exception, it is caught and returned as a Left containing an EffectError tagged with :lift.

Examples

iex> result = Funx.Monad.Effect.lift_func(fn -> 42 end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> result = Funx.Monad.Effect.lift_func(fn -> raise "boom" end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{
  left: %Funx.Errors.EffectError{stage: :lift_func, reason: %RuntimeError{message: "boom"}}
}

@spec lift_maybe(
  Funx.Monad.Maybe.t(right),
  (-> left),
  Funx.Monad.Effect.Context.opts_or_context()
) ::
  t(left, right)
when left: term(), right: term()

Converts a Maybe value into the Effect monad. If the Maybe is Just, the value is wrapped in Right. If it is Nothing, the result of on_none is wrapped in Left.

You can optionally provide context metadata via opts.

Examples

iex> maybe = Funx.Monad.Maybe.just(42)
iex> result = Funx.Monad.Effect.lift_maybe(maybe, fn -> "No value" end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> maybe = Funx.Monad.Maybe.nothing()
iex> result = Funx.Monad.Effect.lift_maybe(maybe, fn -> "No value" end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "No value"}

@spec lift_predicate(
  term(),
  (term() -> boolean()),
  (term() -> left),
  Funx.Monad.Effect.Context.opts_or_context()
) :: t(left, term())
when left: term()

Lifts a value into the Effect monad based on a predicate. If the predicate returns true, the value is wrapped in Right. Otherwise, the result of calling on_false with the value is wrapped in Left.

Optional context metadata (e.g. :span_name, :trace_id) can be passed via opts.

Examples

iex> result = Funx.Monad.Effect.lift_predicate(10, &(&1 > 5), fn x -> "#{x} is too small" end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 10}

iex> result = Funx.Monad.Effect.lift_predicate(3, &(&1 > 5), fn x -> "#{x} is too small" end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "3 is too small"}

@spec map_left(t(error, value), (error -> new_error)) :: t(new_error, value)
when error: term(), new_error: term(), value: term()

Transforms the Left branch of an Effect.

If the Effect resolves to a Left, the provided function is applied to the error. If the Effect resolves to a Right, the value is returned unchanged.

This function is useful when you want to rewrite or wrap errors without affecting successful computations.

Examples

iex> effect = Funx.Monad.Effect.left("error")
iex> transformed = Funx.Monad.Effect.map_left(effect, fn e -> "wrapped: " <> e end)
iex> Funx.Monad.Effect.run(transformed)
%Funx.Monad.Either.Left{left: "wrapped: error"}

iex> effect = Funx.Monad.Effect.pure(42)
iex> transformed = Funx.Monad.Effect.map_left(effect, fn _ -> "should not be called" end)
iex> Funx.Monad.Effect.run(transformed)
%Funx.Monad.Either.Right{right: 42}

@spec pure(right, Funx.Monad.Effect.Context.opts_or_context()) :: t(term(), right)
when right: term()

Alias for right/2.

Wraps a value in the Right variant of the Effect monad, representing a successful asynchronous computation.

Accepts either a keyword list of context options or a Effect.Context struct.

Examples

iex> result = Funx.Monad.Effect.pure(42)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> context = Funx.Monad.Effect.Context.new(trace_id: "custom-id", span_name: "pure example")
iex> result = Funx.Monad.Effect.pure(42, context)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

@spec right(right, Funx.Monad.Effect.Context.opts_or_context()) :: t(term(), right)
when right: term()

Wraps a value in the Right variant of the Effect monad, representing a successful asynchronous computation.

This is an alias for pure/2. You may optionally provide execution context, either as a keyword list or a %Funx.Monad.Effect.Context{} struct. The context is attached to the effect and propagated during execution.

Examples

iex> result = Funx.Monad.Effect.right(42)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> context = Funx.Monad.Effect.Context.new(trace_id: "custom-id", span_name: "from right")
iex> result = Funx.Monad.Effect.right(42, context)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

@spec run(t(left, right)) :: Funx.Monad.Either.t(left, right)
when left: term(), right: term()

Runs the Effect and returns the result, awaiting the task if necessary.

You may provide optional telemetry metadata using opts, such as :span_name to promote the current context with a new label.

Options

• :span_name – (optional) promotes the trace to a new span with the given name.

Examples

iex> result = Funx.Monad.Effect.right(42)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 42}

iex> result = Funx.Monad.Effect.right(42, span_name: "initial")
iex> Funx.Monad.Effect.run(result, span_name: "promoted")
%Funx.Monad.Either.Right{right: 42}

@spec sequence([t(left, right)], Funx.Monad.Effect.Context.opts_or_context()) ::
  t(left, [right])
when left: term(), right: term()

Sequences a list of Effect computations, running each in order.

If all effects resolve to Right, the result is a Right containing a list of values. If any effect resolves to Left, the sequencing stops early and that Left is returned.

Each effect is executed with its own context context, and telemetry spans are emitted for observability.

Examples

iex> effects = [Funx.Monad.Effect.right(1), Funx.Monad.Effect.right(2)]
iex> result = Funx.Monad.Effect.sequence(effects)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: [1, 2]}

iex> effects = [Funx.Monad.Effect.right(1), Funx.Monad.Effect.left("error")]
iex> result = Funx.Monad.Effect.sequence(effects)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "error"}

@spec sequence_a([t(error, value)], Funx.Monad.Effect.Context.opts_or_context()) ::
  t([error], [value])
when error: term(), value: term()

Sequences a list of Effect computations, collecting all Right results or accumulating all Left errors if present.

Unlike sequence/1, which stops at the first Left, this version continues processing all effects, returning a list of errors if any failures occur.

Each effect emits its own telemetry span, and error contexts are preserved through tracing.

Examples

iex> effects = [
...>   Funx.Monad.Effect.right(1),
...>   Funx.Monad.Effect.left("Error 1"),
...>   Funx.Monad.Effect.left("Error 2")
...> ]
iex> result = Funx.Monad.Effect.sequence_a(effects)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: ["Error 1", "Error 2"]}

@spec to_result(
  t(left, right),
  keyword()
) :: {:ok, right} | {:error, left}
when left: term(), right: term()

Converts an Effect into an Elixir {:ok, _} or {:error, _} tuple by running the effect.

If the effect completes successfully (Right), the result is wrapped in {:ok, value}. If the effect fails (Left), the error is returned as {:error, reason}.

This function also emits telemetry via run/2 and supports optional context metadata through keyword options.

Options

• :span_name – sets a custom span name for tracing and telemetry.

Examples

iex> effect = Funx.Monad.Effect.right(42, span_name: "convert-ok")
iex> Funx.Monad.Effect.to_result(effect, span_name: "to_result")
{:ok, 42}

iex> error = Funx.Monad.Effect.left("fail", span_name: "convert-error")
iex> Funx.Monad.Effect.to_result(error, span_name: "to_result")
{:error, "fail"}

Telemetry will include the promoted span name ("to_result -> convert-ok") and context metadata.

@spec to_try!(
  t(left, right),
  keyword()
) :: right | no_return()
when left: term(), right: term()

Executes an Effect and returns the result if it is a Right. If the result is a Left, this function raises the contained error.

This is useful when you want to interoperate with code that expects regular exceptions, such as within test assertions or imperative pipelines.

Runs the effect with full telemetry tracing.

Examples

iex> effect = Funx.Monad.Effect.right(42, span_name: "return")
iex> Funx.Monad.Effect.to_try!(effect)
42

iex> error = Funx.Monad.Effect.left(%RuntimeError{message: "failure"}, span_name: "error")
iex> Funx.Monad.Effect.to_try!(error)
** (RuntimeError) failure

Telemetry will emit a :stop event with :status set to :ok or :error, depending on the outcome.

Traverses a list with a function that returns Effect computations, running each in sequence and collecting the Right results.

If all effects resolve to Right, returns a single Effect with a list of results. If any effect resolves to Left, the traversal stops early and returns that Left.

Each step preserves context context and emits telemetry spans, including nested spans when bound.

Examples

iex> is_positive = fn num ->
...>   Funx.Monad.Effect.lift_predicate(num, fn x -> x > 0 end, fn x -> Integer.to_string(x) <> " is not positive" end)
...> end
iex> result = Funx.Monad.Effect.traverse([1, 2, 3], fn num -> is_positive.(num) end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: [1, 2, 3]}
iex> result = Funx.Monad.Effect.traverse([1, -2, 3], fn num -> is_positive.(num) end)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: "-2 is not positive"}

Traverses a list with a function that returns Effect values, combining results into a single Effect. Unlike traverse/2, this version accumulates all errors rather than stopping at the first Left.

Each successful computation contributes to the final list of results. If any computations fail, all errors are collected and returned as a single Left.

This function also manages telemetry trace context across all nested effects, ensuring that span relationships and trace IDs are preserved through the traversal.

Examples

iex> validate = fn n ->
...>   Funx.Monad.Effect.lift_predicate(n, fn x -> x > 0 end, fn x -> Integer.to_string(x) <> " is not positive" end)
...> end
iex> result = Funx.Monad.Effect.traverse_a([1, -2, 3], validate)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: ["-2 is not positive"]}
iex> result = Funx.Monad.Effect.traverse_a([1, 2, 3], validate)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: [1, 2, 3]}

@spec validate(
  value,
  (value -> t(error, any())) | [(value -> t(error, any()))],
  Funx.Monad.Effect.Context.opts_or_context()
) :: t([error], value)
when error: term(), value: term()

Validates a value using one or more validator functions, each returning an Effect.

If all validators succeed (Right), the original value is returned in a Right. If any validator fails (Left), all errors are accumulated and returned as a single Left.

This function also manages telemetry trace context across all nested validations, ensuring that span relationships and trace IDs are preserved throughout.

Supports optional opts for span metadata (e.g. :span_name).

Examples

iex> validate_positive = fn x ->
...>   Funx.Monad.Effect.lift_predicate(x, fn n -> n > 0 end, fn n -> "Value " <> Integer.to_string(n) <> " must be positive" end)
...> end
iex> validate_even = fn x ->
...>   Funx.Monad.Effect.lift_predicate(x, fn n -> rem(n, 2) == 0 end, fn n -> "Value " <> Integer.to_string(n) <> " must be even" end)
...> end
iex> validators = [validate_positive, validate_even]
iex> result = Funx.Monad.Effect.validate(4, validators)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Right{right: 4}
iex> result = Funx.Monad.Effect.validate(3, validators)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: ["Value 3 must be even"]}
iex> result = Funx.Monad.Effect.validate(-3, validators)
iex> Funx.Monad.Effect.run(result)
%Funx.Monad.Either.Left{left: ["Value -3 must be positive", "Value -3 must be even"]}