Overview

Module passage_transform

• Description
• Data Types
• Function Index
• Function Details

Copyright © 2017 Takeru Ohta <phjgt308@gmail.com>

Description

A parse_transform module for passage

This module handles passage_trace attribute.

If the attribute is appeared, the next function will be traced automatically.

See following example:

  -module(example).
 
  -compile({parse_transform, passage_transform}). % Enables `passage_transform'
 
  -passage_trace([{tags, #{foo => bar}}, {eval_tags, #{size => "byte_size(Bin)"}}]).
  -spec foo(binary()) -> binary().
  foo(Bin) ->
    <<"foo", Bin/binary>>.

The above foo function will be transformed as follows:

  foo(Bin) ->
    try
      passage_pd:start_span(
        'example:foo/1',
        [{tags, #{application => example, module => example, line => 7, foo => bar}}]),
      passage_pd:set_tags(#{process => self(), size => byte_size(Bin)}),
      <<"foo", Bin/binary>>
    after
      passage_pd:finish_span()
    end.

References

• The Abstract Format

Data Types

expr_string()

expr_string() = string()

The textual representation of an expression.

When used, it will be converted to an AST representation as follows:

  {ok, Tokens, _} = erl_scan:string(ExprString ++ "."),
  {ok, [Expr]} = erl_parse:parse_exprs(Tokens).

passage_trace_option()

passage_trace_option() = {tracer, passage:tracer_id()} | {tags, passage:tags()} | {eval_tags, #{passage:tag_name() => expr_string()}} | {child_of, expr_string()} | {follows_from, expr_string()} | {error_if, expr_string()} | error_if_exception

• tracer: See passage:start_span/2
• tags: See passage:start_span/2
• eval_tags: This is the same as tags except the values are dynamically evaluated in the transforming phase.
• child_of: See passage:start_span/2
• follows_from: See passage:start_span/2
• error_if

    %% {error_if, ErrorPattern}
    case Body of
      ErrorPattern = Error ->
        passage_pd:log(#{message, Result}, [error]),
        Error;
      Ok -> Ok
    end.

• error_if_exception:

    try
      Body
    catch
      Class:Error ->
        passage_pd:log(#{'error.kind' => class,
                         'message' => Error,
                         'stack' => erlang:get_stacktrace()},
                       [error]),
        erlang:raise(Class, Error, erlang:get_stacktrace())
    end.

Function Index

Function Details

parse_transform/2

Performs transformations for passage

Overview

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