format 2.0: abstraction as library, in D and Gleam

2026-09-26T13:47:07+00:00
The object-centric document abstraction that sisudoc-spine builds from
SiSU markup, read as a library: the model, and a loader for each form
it is written in - the .ssp (text), the .ocda.db (sqlite), and a pod
archive carrying a .ssp (.sisupod, .zip). Begun 2026-09-25; this is
the library as it stood at format 2.0.

The readers (sisudoc-ssp-reader, sisudoc-ocda-db-reader) each read one
form and print. A writer needs neither: it needs the document. So the
model and the loaders live here, ocda.model imports nothing, and a
program built on the library cannot tell which form it was handed.
ocda.load is the one place that decides what a path is, so a new
input form is added once and every program gains it. The model and
the .ssp loader began as the .ssp reader's code, moved and renamed to
the level they belong to; the .ocda.db loader is new.

The Gleam library is a deliberate field-for-field mirror of the D one,
including where that is not the most idiomatic Gleam: a difference in
one language and not the other would show in every comparison and
mean nothing.

The claim holds only if the loaders agree, so the library asks:

  ocda-agree  .ssp .ocda.db [lang]   ten fields, per object
  ocda-dump    [lang]                    the whole model,
                                               canonically

The dump is an oracle, not an output format, and the D and Gleam
dumps are byte identical, so four questions are a diff: D and Gleam,
each from the .ssp and from the .ocda.db. Over the markup document
samples all four hold, every document-language; a .sisupod gives the
same model as the .ssp beside it.

None of that held at first, and what the checks found is the record
of how the specification became enough:

- an object whose first text line is blank lost it (the loader asked
  whether the text was empty, not whether a line had been seen);
  seven sample documents open verse that way. Found by agree; fixed
  here and in the .ssp reader, which carried the same code.
- found by the dump: the identifier and the anchor are omitted by the
  text form when they can be derived and stored by the database
  always, so the loaders derive them, and the rule went into the
  specification (derived values); make and doc_has share one table in
  the database under a key prefix, which the loaders strip; the JSON
  columns were scanned, not parsed, and Phobos writes "/" as "\/";
  and translation.ocn_aligned is a fact about the file, not the
  document, so neither loader puts it in the model.
- in Gleam, a JSON element decoder fell through to a fallback giving
  "", so a float column read as empty strings: a value that could not
  be read turned into one that looked read.
- found by the writers: anchor_tags, heading_lev_anchor, segment_epub
  and segment_epub_is were in the specification and read by nothing.

ocda.images gives an image's bytes from whichever form the document
came from (the database's files table, the archive entry, or beside
a .ssp at media/image/), and says beforehand whether it can.

The Gleam library reads a .zip pod but not a .sisupod: the zstd frame
around it has no implementation on the BEAM that builds sandboxed. It
says so, and says zstd -d, rather than calling the file malformed.

gleam/ builds with nix-gleam's builder, kept in gleam/nix-gleam/ (MIT)

Use:

  dlang/  nix build        ocda-dump, ocda-agree; or a dub path
                           dependency on dlang/
  gleam/  nix build        ocda-lib dump | agree

See README.md, and dlang/README.md and gleam/README.md.

(assisted by Claude-Code)
sisudoc-ocda-lib/.gitignore, branch main

format 2.0: abstraction as library, in D and Gleam
