lfe_error.erl - Error Formatting

Purpose: Format exceptions and errors for user-friendly display.

Location: src/lfe_error.erl Size: 171 LOC, 5.7KB

Module Classification: Utilities, error handling

Public API

format_exception(Class, Reason, StackTrace) -> Chars
format_exception(Class, Reason, StackTrace, SkipFun, FormatFun, Indentation) -> Chars

Format exception with stack trace. Located at lfe_error.erl:39-52.

Parameters:

• Class - error, throw, or exit
• Reason - Exception reason
• StackTrace - List of stack frames
• SkipFun - Function to filter stack frames
• FormatFun - Function to format terms
• Indentation - Initial indentation level

Exception Formatting

Output Format:

exception error: badarg
  in (lfe_eval:eval_expr/2 line 345)
  in (lfe_shell:eval_form/2 line 502)

Stack Trace Filtering (filter_stack/2 at lines 87-112):

Allows skipping internal frames:

SkipFun = fun(Module, _Function, _Arity) ->
    Module == lfe_eval orelse Module == lfe_shell
end

Term Formatting (format_term/3 at lines 134-156):

Custom formatting for exception data:

FormatFun = fun(Term, Indent) ->
    lfe_io:prettyprint1(Term, 15, Indent, 80)
end

Exception Classes

Error (runtime errors):

exception error: badarg

Throw (user throws):

exception throw: my_exception

Exit (process exits):

exception exit: normal

Stack Frame Format

Erlang Stack Frame:

{Module, Function, Arity, [{file, File}, {line, Line}]}

Formatted:

in (Module:Function/Arity line Line)
in (Module:Function/Arity File:Line)

Dependencies

LFE modules:

• lfe_io - Term formatting

Erlang stdlib:

• lists, string

Used By

• lfe_shell - Exception reporting
• lfe_init - Script error reporting
• lfescript - Script errors

Special Considerations

User-Friendly: Formats for human readability, not machine parsing.

Filtering: Can hide internal implementation details from users.

Customizable: Format function allows LFE-style or Erlang-style output.