Elixir

v1.8.1

Exception behaviour View Source

Functions to format throw/catch/exit and exceptions.

Note that stacktraces in Elixir are only available inside catch and rescue by using the __STACKTRACE__/0 variable.

Do not rely on the particular format returned by the format* functions in this module. They may be changed in future releases in order to better suit Elixir's tool chain. In other words, by using the functions in this module it is guaranteed you will format exceptions as in the current Elixir version being used.

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Types

kind()

The kind handled by formatting functions

stacktrace()
stacktrace_entry()
t()

The exception type

Functions

blame(kind, error, stacktrace)

Attaches information to exceptions for extra debugging

blame_mfa(module, function, args)

Blames the invocation of the given module, function and arguments

exception?(term)

Returns true if the given term is an exception

format(kind, payload, stacktrace \\ [])

Normalizes and formats throw/errors/exits and stacktraces

format_banner(kind, exception, stacktrace \\ [])

Normalizes and formats any throw/error/exit

format_exit(reason)

Formats an exit. It returns a string

format_fa(fun, arity)

Receives an anonymous function and arity and formats it as shown in stacktraces. The arity may also be a list of arguments

format_file_line(file, line, suffix \\ "")

Formats the given file and line as shown in stacktraces. If any of the values are nil, they are omitted

format_mfa(module, fun, arity)

Receives a module, fun and arity and formats it as shown in stacktraces. The arity may also be a list of arguments

format_stacktrace(trace \\ nil)

Formats the stacktrace

format_stacktrace_entry(entry)

Receives a stacktrace entry and formats it into a string

message(exception)

Gets the message for an exception

normalize(kind, payload, stacktrace \\ [])

Normalizes an exception, converting Erlang exceptions to Elixir exceptions

Callbacks

blame(t, stacktrace)

Called from Exception.blame/3 to augment the exception struct

exception(term)
message(t)

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kind() View Source 
kind() :: :error | non_error_kind()

The kind handled by formatting functions

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stacktrace() View Source 
stacktrace() :: [stacktrace_entry()]

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stacktrace_entry() View Source 
stacktrace_entry() ::
  {module(), atom(), arity_or_args(), location()}
  | {(... -> any()), arity_or_args(), location()}

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t() View Source 
t() :: %module(){:__exception__ => true, optional(atom()) => any()}

The exception type

Link to this section Functions

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blame(kind, error, stacktrace) View Source (since 1.5.0) 
blame(:error, any(), stacktrace()) :: {t(), stacktrace()}
blame(non_error_kind(), payload, stacktrace()) :: {payload, stacktrace()}
when payload: var

Attaches information to exceptions for extra debugging.

This operation is potentially expensive, as it reads data from the file system, parses beam files, evaluates code and so on.

If the exception module implements the optional blame/2 callback, it will be invoked to perform the computation.

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blame_mfa(module, function, args) View Source (since 1.5.0) 
blame_mfa(module(), function(), args :: [term()]) ::
  {:ok, :def | :defp | :defmacro | :defmacrop,
   [{args :: [term()], guards :: [term()]}]}
  | :error

Blames the invocation of the given module, function and arguments.

This function will retrieve the available clauses from bytecode and evaluate them against the given arguments. The clauses are returned as a list of {args, guards} pairs where each argument and each top-level condition in a guard separated by and/or is wrapped in a tuple with blame metadata.

This function returns either {:ok, definition, clauses} or :error. Where definition is :def, :defp, :defmacro or :defmacrop.

Returns true if the given term is an exception.

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format(kind, payload, stacktrace \\ []) View Source 
format(kind(), any(), stacktrace()) :: String.t()

Normalizes and formats throw/errors/exits and stacktraces.

It relies on format_banner/3 and format_stacktrace/1 to generate the final format.

If kind is {:EXIT, pid}, it does not generate a stacktrace, as such exits are retrieved as messages without stacktraces.

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format_banner(kind, exception, stacktrace \\ []) View Source 
format_banner(kind(), any(), stacktrace()) :: String.t()

Normalizes and formats any throw/error/exit.

The message is formatted and displayed in the same format as used by Elixir's CLI.

The third argument is the stacktrace which is used to enrich a normalized error with more information. It is only used when the kind is an error.

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format_exit(reason) View Source 
format_exit(any()) :: String.t()

Formats an exit. It returns a string.

Often there are errors/exceptions inside exits. Exits are often wrapped by the caller and provide stacktraces too. This function formats exits in a way to nicely show the exit reason, caller and stacktrace.

Receives an anonymous function and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.

Examples 

Exception.format_fa(fn -> nil end, 1)
#=> "#Function<...>/1"
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format_file_line(file, line, suffix \\ "") View Source

Formats the given file and line as shown in stacktraces. If any of the values are nil, they are omitted.

Examples 

iex> Exception.format_file_line("foo", 1)
"foo:1:"

iex> Exception.format_file_line("foo", nil)
"foo:"

iex> Exception.format_file_line(nil, nil)
""
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format_mfa(module, fun, arity) View Source

Receives a module, fun and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.

Examples 

iex> Exception.format_mfa(Foo, :bar, 1)
"Foo.bar/1"

iex> Exception.format_mfa(Foo, :bar, [])
"Foo.bar()"

iex> Exception.format_mfa(nil, :bar, [])
"nil.bar()"

Anonymous functions are reported as -func/arity-anonfn-count-, where func is the name of the enclosing function. Convert to "anonymous fn in func/arity"

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format_stacktrace(trace \\ nil) View Source

Formats the stacktrace.

A stacktrace must be given as an argument. If not, the stacktrace is retrieved from Process.info/2.

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format_stacktrace_entry(entry) View Source 
format_stacktrace_entry(stacktrace_entry()) :: String.t()

Receives a stacktrace entry and formats it into a string.

Gets the message for an exception.

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normalize(kind, payload, stacktrace \\ []) View Source 
normalize(:error, any(), stacktrace()) :: t()
normalize(non_error_kind(), payload, stacktrace()) :: payload when payload: var

Normalizes an exception, converting Erlang exceptions to Elixir exceptions.

It takes the kind spilled by catch as an argument and normalizes only :error, returning the untouched payload for others.

The third argument is the stacktrace which is used to enrich a normalized error with more information. It is only used when the kind is an error.

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blame(t, stacktrace) View Source (optional) 
blame(t(), stacktrace()) :: {t(), stacktrace()}

Called from Exception.blame/3 to augment the exception struct.

Can be used to collect additional information about the exception or do some additional expensive computation.

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exception(term) View Source 
exception(term()) :: t()