Normalize Elixir temporal structs (DateTime, NaiveDateTime, Date, Time) to ISO 8601 strings before they cross any boundary into LLM-visible territory.

Why this exists

Elixir's Inspect protocol renders temporal structs with sigil syntax:

iex> inspect(~U[2026-05-03 09:14:00Z])
"~U[2026-05-03 09:14:00Z]"

That's idiomatic Elixir, but every downstream consumer that expects a parseable date string (the LLM, JSON Schema validators, (java.util.Date. ...) in PTC-Lisp) breaks when it sees the sigil. ISO 8601 is the universal lingua franca for temporal data.

This module is the central seam: any code that exposes Elixir data to an LLM or to PTC-Lisp should normalize through iso8601/1 (for known scalar position) or walk/1 (for arbitrary nested data like tool results).

Functions

• iso8601/1 — convert a single value. Pass-through for non-temporal terms.
• walk/1 — recursively normalize temporal structs inside maps and lists, leaving everything else alone.

Examples

iex> PtcRunner.Temporal.iso8601(~U[2026-05-03 09:14:00Z])
"2026-05-03T09:14:00Z"

iex> PtcRunner.Temporal.iso8601(~D[2026-05-03])
"2026-05-03"

iex> PtcRunner.Temporal.iso8601(~N[2026-05-03 09:14:00])
"2026-05-03T09:14:00"

iex> PtcRunner.Temporal.iso8601(~T[09:14:00])
"09:14:00"

iex> PtcRunner.Temporal.iso8601("hello")
"hello"

iex> PtcRunner.Temporal.iso8601(nil)
nil

iex> PtcRunner.Temporal.walk(%{at: ~D[2026-05-03], items: [~T[09:14:00]]})
%{at: "2026-05-03", items: ["09:14:00"]}