It is fine to question the legitimacy, as long as it is accurate and constructive. Calling it a toy problem is neither. You could instead have asked: “can you provide more context about the problem statement?”. Also, it is not hard for us to try to find where we can apply this to.
I grepped Livebook and I found this:
{sections, {_branching_ids, warnings}} =
notebook.sections
|> Enum.with_index()
|> Enum.map_reduce({MapSet.new(), []}, fn {section, section_idx},
{branching_ids, warnings} ->
# Set parent_id based on the persisted branch_parent_index if present
case section.parent_id do
nil ->
{section, {branching_ids, warnings}}
{:idx, parent_idx} ->
parent = Enum.at(notebook.sections, parent_idx)
cond do
section_idx <= parent_idx ->
{%{section | parent_id: nil},
{
branching_ids,
[
~s{ignoring the parent section of "#{section.name}", because it comes later in the notebook}
| warnings
]
}}
!is_nil(parent) && MapSet.member?(branching_ids, parent.id) ->
{%{section | parent_id: nil},
{
branching_ids,
[
~s{ignoring the parent section of "#{section.name}", because it is itself a branching section}
| warnings
]
}}
true ->
{%{section | parent_id: parent.id},
{MapSet.put(branching_ids, section.id), warnings}}
end
end
end)
and with this proposal that could be rewritten to:
@@warnings = []
@@branching_ids = MapSet.new()
for {section, section_idx} <- Enum.with_index(notebook.sections) do
case section.parent_id do
nil ->
section
{:idx, parent_idx} ->
parent = Enum.at(notebook.sections, parent_idx)
cond do
section_idx <= parent_idx ->
@@warnings = [
~s{ignoring the parent section of "#{section.name}", because it comes later in the notebook}
| @@warnings
]
%{section | parent_id: nil}
!is_nil(parent) and MapSet.member?(@@branching_ids, parent.id) ->
@@warnings = [
~s{ignoring the parent section of "#{section.name}", because it is itself a branching section}
| @@warnings
]
%{section | parent_id: nil}
true ->
@@branching_ids = MapSet.put(@@branching_ids, section.id)
%{section | parent_id: parent.id}
end
end
end)
Is it better? Worse? You decide.
So if we want to question the problem statement, let’s put the work into it. 
I would immediately break this code in smaller chunks.
I just don’t want problems to be dismissed for the wrong reasons.
