Dr. Christian Geuer-Pollmann

@christian.geuer-pollmann.de

Principal Engineer working on @Azure, security & cloud architect, Apache Committer, DG5EAW, http://genserver.social/chgeuer. Private account. #ElixirLang. Archive https://bsky.app/profile/chgeuer.bsky.social

Screenshot of https://github.com/chgeuer/copilot_lv

Screenshot from https://github.com/chgeuer/copilot_lv that allows me to see what https://github.com/chgeuer/jido_symphony does on the LLM side, including all tool calls

Phoenix liveview UI of Symphony running a "recreate x.com in Phoenix LiveView" loop

Screenshot of bash sessions of the LLM using the BEAM introspection skill to figure out which Erlang processes have most reductions.

The Technology Choice That Haunted My Exit

Let me tell you a story that really drove this home for me. I had this technology choice problem with my previous business that I sold, Feedback Panda, which was built on top of a rather rarely seen web server called Phoenix in the Elixir programming language. And that, in many ways, quite limited who would be able to buy our company or buy our product, because they would have to have an Elixir engineer.

Whereas everybody has access to many, many PHP and Ruby and JavaScript engineers, Elixir engineers are still in high demand, and the engineers that can work with this technology have spent many years figuring it out—they are more expensive than others. So in a way, that choice probably precluded us from several buyers, potential buyers, just by the mere tech choice that we made.

Even though we had this wonderful application that we thought we owned, when somebody asked, “Well, can I buy it from you? What tech do you use?”—your ownership, not just in terms of the software, the code itself, but also the decision of which code to write, matters tremendously.

$C:\Users\chgeuer λ dir fun_test.* Volume in drive C is C Volume Serial Number is 72BC-3429 Directory of C:\Users\chgeuer 21.09.2025 10:35 50 fun_test.erl 1 File(s) 50 bytes 0 Dir(s) 1.044.067.782.656 bytes free C:\Users\chgeuer λ which erlc.exe /c/Users/chgeuer/.elixir-install/installs/otp/28.0.1/bin/erlc.exe C:\Users\chgeuer λ erlc.exe fun_test.erl C:\Users\chgeuer λ dir fun_test.* Volume in drive C is C Volume Serial Number is 72BC-3429 Directory of C:\Users\chgeuer 21.09.2025 10:37 588 fun_test.beam 21.09.2025 10:35 50 fun_test.erl 2 File(s) 638 bytes 0 Dir(s) 1.043.897.606.144 bytes free C:\Users\chgeuer λ type fun_test.erl -module(fun_test). -export([t1/0]). t1() -> 1. C:\Users\chgeuer$

$defmodule Calculator do use ReactiveStruct, allow_updating_computed_fields: false defstruct ~w(a0 a b sum product)a computed(:a, fn %{a0: a0} -> a0 + 1 end) computed :sum, fn %{a: a, b: b} -> a + b end computed :product, fn %{a: a, b: b} -> a * b end end$

Elixir code:

defmodule Chain do
use ReactiveStruct
defstruct ~w[base step1 step2 final]a

computed(:final, deps: [:step2], do: step2 * step2)
computed(:step1, deps: [:base], do: base * 2)
computed(:step2, deps: [:step1], do: step1 + 10)
end

chain = %{final: 256} = Chain.new(base: 3)
chain = %{final: 400} = Chain.update(chain, base: 5)

Elixir code

defmodule SomeStruct do
use ReactiveStruct

defstruct ~w{x2 x3 x ya yb y sum}a

computed(:y, deps: [:ya, :yb], do: ya - yb)
computed(:x, deps: [:x2, :x3], do: x2 + x3)
computed(:sum, deps: [:x, :y], do: x * y)
end

SomeStruct.new(x2: 2, x3: 3, ya: 4, yb: 5)
|> IO.inspect(label: :a)
|> SomeStruct.update(x2: 10)
|> IO.inspect(label: :b)

Kino.Mermaid.new(SomeStruct.mermaid())

and a Mermaid diagram

$defmodule Claude do def sample_function do # You can call this from bash using the command # # $ mix run -e "IO.inspect(Claude.sample_function())" # # It should output # {"Yeah", :stuff} {"Yeah", :stuff} end$

SCOPE:
Vulnerabilities in active packages hosted on Hex.pm, and in active projects hosted under the GitHub organizations @elixir-lang, @erlang, @erlef-cna, @erlef, @gleam-lang, and @hexpm, unless covered by the scope of another CNA.
CNA ID:
CNA-2025-0023

$A LiveBook calling into DNSimple to fetch records. DNSimple.Ash.Domain.list_zone_records_for_zone!( "geuer-pollmann.de", query: [ filter: [type: "A", name_like: "shel"], sort: [name: :asc], #limit: 5 ] ) |> Enum.map(&{&1.name, &1.content})$