[erlang-questions] Trace erlang BIFs with dbg

Lukas Larsson <>
Mon Sep 12 10:20:50 CEST 2016


It is not possible to trace on what is called "guard bifs", i.e. functions
in the erlang module that can be used in guards. For a full list of which
those function are see:


On Fri, Sep 9, 2016 at 11:56 PM, nato <> wrote:

> Are BIFs such as `length/1` part of the erlang module, or do BIFs live
> somewhere else then get masqueraded ...
> I am trying to trace functions like these with dbg, and nothing is yielded.
> For example, I am trying the following with no success...
> 1> dbg:tracer(), dbg:p(all, c).
> 2> dbg:tpl(erlang, length, x).
> 3> erlang:length( [] ). %% or simply `length([]).`
> Or, are my above dbg flags leaving the erlang module out... or... confused.
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