Base behaviour and helpers for typed HL7v2 segments.

Provides a __using__ macro that generates struct, parse/2, and encode/1 from a declarative field definition list — zero boilerplate per segment.

Defining a Segment

defmodule HL7v2.Segment.MSA do
  use HL7v2.Segment,
    id: "MSA",
    fields: [
      {1, :acknowledgment_code, HL7v2.Type.ID, :r, 1},
      {2, :message_control_id, HL7v2.Type.ST, :r, 1},
      {3, :text_message, HL7v2.Type.ST, :o, 1},
      ...
    ]
end

Field Definitions

Each field is a tuple {sequence, name, type, optionality, max_reps}:

• sequence — 1-based field position per HL7 spec
• name — atom used as struct key
• type — type module (e.g. HL7v2.Type.ST) or :raw for pass-through
• optionality — :r (required), :o (optional), :c (conditional), :b (backwards-compat/withdrawn)
• max_reps — 1 for non-repeating, :unbounded or integer for repeating