@spec new() :: t()

Creates a new Extep struct with an empty context.

Examples

iex> Extep.new()
%Extep{status: :ok, context: %{}, message: nil}

@spec new(map()) :: t()

Creates a new Extep struct with an initial context map.

Examples

iex> Extep.new(%{foo: "bar"})
%Extep{status: :ok, context: %{foo: "bar"}, message: nil}

@spec return(t(), context_mutator_fun() | context_key(), opts()) :: any()

Returns a final result from your pipeline with optional configuration.

This function extracts the final result from your pipeline based on the pipeline's status:

• :ok status: Executes the given function or returns the context value for the given key
• :halted status: Returns the halt message (ignores all options)
• :error status: Returns an error tuple, optionally with or without context labels

Parameters

• extep - The Extep struct containing your pipeline state
• fun_or_key - Either a function (context -> result) or an atom key to extract from context
• opts - Keyword list of options (defaults to [])

Options

• label_error (boolean, default: false):
  • When false: Returns clean error messages like {:error, "message"}
  • When true: Returns labeled errors like {:error, %{fun_name_or_step_name: "message"}}

Examples

Successful Pipeline with Function

When the pipeline succeeds, the function is executed with the context:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.return(fn ctx -> {:ok, ctx.bar + 2} end)
{:ok, 4}

Successful Pipeline with Context Key

When the pipeline succeeds, the value for the given key is returned:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.run(:baz, fn ctx -> {:ok, ctx.bar + 2} end)
...> |> Extep.return(:bar)
{:ok, 2}

Error Pipeline with Default Behavior (Clean Errors)

When the pipeline errors and no options are provided, returns clean error messages:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn _ctx -> {:error, "error message"} end)
...> |> Extep.return(:foo)
{:error, "error message"}

Error Pipeline with Function and Labeled Errors

When label_error: true is set and a named function causes the error, the error is labeled with the function name:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.return(&return_error_tuple/1, label_error: true)
{:error, %{return_error_tuple: "error message"}}

Error Pipeline with Anonymous Function and Labeled Errors

When label_error: true is set and an anonymous function causes the error, the error is labeled with :no_label:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.return(fn _ctx -> {:error, "error message"} end, label_error: true)
{:error, %{no_label: "error message"}}

Error Pipeline with Context Key and Labeled Errors

When label_error: true is set and a step with a context key caused the error, the error is labeled with that step's name:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn _ctx -> {:error, "error message"} end)
...> |> Extep.return(:foo, label_error: true)
{:error, %{bar: "error message"}}

Halted Pipeline Returning Function Result

When a function in the pipeline halts with a result, that result is returned directly:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.return(fn _ctx -> {:halt, {:ok, "halt message"}} end)
{:ok, "halt message"}

Halted Pipeline Returning Custom Tuple

Halt messages can be any term, not just ok tuples:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.return(fn _ctx -> {:halt, {:cancel, "cancel message"}} end)
{:cancel, "cancel message"}

Previously Halted Pipeline

When the pipeline was already halted in a previous step, the halt message is returned regardless of what you're trying to return:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.run(:baz, fn _ctx -> {:halt, {:ok, "halt message"}} end)
...> |> Extep.return(:bar)
{:ok, "halt message"}

@spec run(t(), context_checker_fun()) :: t()

Runs a checker function on the context without modifying it.

This function is useful for validation, checking conditions, or performing side effects without changing the pipeline context. The context remains unchanged regardless of the function's return value.

Function Return Values

The checker function must return one of these values:

• :ok - Pipeline continues with unchanged context
• {:ok, value} - Pipeline continues with unchanged context (value is ignored)
• {:halt, reason} - Pipeline stops with :halted status, reason stored in message
• {:error, reason} - Pipeline stops with :error status, reason stored in message

Error Message Labeling

When errors occur, the message is stored differently based on the function type:

• Named functions: Error labeled with function name (e.g., %{validate_user: "error"})
• Anonymous functions: Error labeled with :no_label (e.g., %{no_label: "error"})

Examples

Successful Validation - Simple OK

Basic validation that passes without returning a value:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(fn _ctx -> :ok end)
%Extep{status: :ok, context: %{foo: 1}, message: nil}

Successful Validation - OK tuple

Validation that passes and returns an ok tuple (value is ignored, context unchanged):

iex> Extep.new(%{foo: 1})
...> |> Extep.run(fn _ctx -> {:ok, "is valid"} end)
%Extep{status: :ok, context: %{foo: 1}, message: nil}

Error with Named Function

When a named function returns an error tuple, the error is labeled with the function name:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(&return_error_tuple/1)
%Extep{status: :error, context: %{foo: 1}, message: %{return_error_tuple: "error message"}}

Error with Anonymous Function

When an anonymous function returns an error tuple, the error is labeled with :no_label:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(fn _ctx -> {:error, "error message"} end)
%Extep{status: :error, context: %{foo: 1}, message: %{no_label: "error message"}}

Halt Example

When a function returns a halt tuple, the pipeline stops and the halt reason is stored:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(fn _ctx -> {:halt, {:ok, "halt message"}} end)
%Extep{status: :halted, context: %{foo: 1}, message: {:ok, "halt message"}}

It's useful when you want to stop the pipeline and return a specific message, like a cancel tuple for an Oban job, for example:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(fn _ctx -> {:halt, {:cancel, "cancel message"}} end)
...> |> Extep.return(fn ctx -> {:ok, ctx.bar + 2} end)
{:cancel, "cancel message"}

Pipeline Behavior

• If the Extep struct already has :halted or :error status, this function does nothing
• Only processes when the current status is :ok
• The context is never modified by this function

@spec run(t(), context_key(), context_mutator_fun()) :: t()

Runs a mutator function that updates the context with the result under the given key.

This function executes a mutator function and stores its result in the context under the specified key. Unlike run/2, this function is designed to modify the context by adding or updating values.

Parameters

• extep - The current Extep struct
• context_key - An atom representing the key where the result will be stored
• fun - A function that takes the context and returns a result

Function Return Values

The mutator function must return one of these values:

• {:ok, value} - Pipeline continues, value is stored under context_key
• {:halt, reason} - Pipeline stops with :halted status, reason stored in message
• {:error, reason} - Pipeline stops with :error status, reason stored in message

Note: Unlike run/2, this function does NOT accept plain :ok returns. It requires a tuple with a value to store in the context.

Error Message Labeling

When errors occur, the message is stored differently based on the function type:

• Named functions: Error labeled with function name (e.g., %{fetch_user: "error"})
• Anonymous functions: Error labeled with the context key (e.g., %{user: "error"})

Examples

Successful Context Updates

This example shows how values are stored and can be used by subsequent steps:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:foo, fn ctx -> {:ok, ctx.foo + 1} end)
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 2} end)
%Extep{status: :ok, context: %{foo: 2, bar: 4}, message: nil}

Explanation:

• First run/3 updates :foo from 1 to 2
• Second run/3 adds :bar with value 4 (using the updated foo value: 2 + 2)
• Both operations succeed, context now contains both updated values

Error with Named Function - Pipeline Stops

When a named function returns an error, the pipeline stops and subsequent steps are skipped:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:foo, &return_error_tuple/1)
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 2} end)
%Extep{status: :error, context: %{foo: 1}, message: %{return_error_tuple: "error message"}}

Explanation:

• First run/3 calls return_error_tuple/1 which returns {:error, "error message"}
• Pipeline status becomes :error, original context is preserved
• Error message is labeled with function name (return_error_tuple)
• Second run/3 is skipped because pipeline is already in error state

Error with Anonymous Function - Pipeline Stops

When an anonymous function returns an error, the error is labeled with the context key:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:foo, fn _ctx -> {:error, "error message"} end)
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 2} end)
%Extep{status: :error, context: %{foo: 1}, message: %{foo: "error message"}}

Explanation:

• First run/3 tries to update :foo but returns an error
• Pipeline status becomes :error, original context is preserved
• Error message is labeled with the context key (:foo)
• Second run/3 is skipped because pipeline is already in error state

Halt with Custom Message - Pipeline Stops

When a function returns halt, the pipeline stops gracefully with the halt message:

iex> Extep.new(%{foo: 1})
...> |> Extep.run(:foo, fn _ctx -> {:halt, {:ok, "halt message"}} end)
...> |> Extep.run(:bar, fn ctx -> {:ok, ctx.foo + 2} end)
%Extep{status: :halted, context: %{foo: 1}, message: {:ok, "halt message"}}

Explanation:

• First run/3 returns a halt tuple with {:ok, "halt message"}
• Pipeline status becomes :halted, original context is preserved
• Halt message can be any term (here it's {:ok, "halt message"})
• Second run/3 is skipped because pipeline is already halted

Pipeline Behavior

• If the Extep struct already has :halted or :error status, this function does nothing
• Only processes when the current status is :ok
• On success, the context is updated with the new value under the specified key
• On failure or halt, the context remains unchanged
• Context keys can be new (adding) or existing (updating)