yapyon (やぴょん)

「YAMLちゃうで。やぴょんやぴょん」 It's not YAML. It's yapyon.

Python-style typed literals with YAML-like block structure. Quoted strings, True/False/None, indentation blocks, - sequences, + multimaps, # comments — and parse-time splicing that replaces YAML's anchors.

name: "api-gateway"
version: 3.10
port: 8080
debug: False

paths:
  root: "/srv/gateway"
  logs: y"{root}/logs"          # -> "/srv/gateway/logs"
  banner: y"{name} v{version}"  # -> "api-gateway v3.10"   (lexeme, not 3.1)

changes:                        # multimap: keys may repeat, order is data
  + registry: {set: ["Bypass"]}
  + file: {delete: ["Edge"]}
  + registry: {remove: ["Edge Update"]}

The pitch: the same bytes mean the same data, to every parser, on every machine, always. No implicit typing (no is not False; there are no unquoted scalars at all), no anchors, no tags, no evaluation, one null spelling, one document per file. A repeated key is an error unless the block says + , so it can never be mistaken for a typo — or silently collapsed, the way Python and YAML both drop {"a": 1, "a": 2} down to one entry.

Status

Pre-alpha, and the a in the version means it. Lexer, parser, resolver, loader and emitter are done and tested — 592 tests, including a conformance suite that turns the splice matrix and the Python divergence table into executable cases.

The normative specification is published, in two documents under docs/:

docs/GRAMMAR.md	are these bytes well-formed yapyon? — self-contained, normative for syntax
docs/SPEC.md	what do well-formed bytes mean? — normative for meaning

References run one way: the spec cites the grammar, the grammar cites nothing. A parser can be written from the grammar alone, which is the point of separating them. This README summarises the format; those documents define it.

Identifiers are UAX #31, pinned to Unicode 14.0.0, with invisible characters excluded. yapyon ships its own table rather than asking the interpreter, so a key means the same thing on every install and every Python. Width variants and canonically equivalent spellings are the same name — ｎａｍｅ is name, and é is é however it was composed — while fi and fi stay distinct. yapyon.UNICODE_VERSION names the pinned version.

$ pip install --pre yapyon

>>> import yapyon
>>> yapyon.loads('name: "gw"\nport: 8080\naddr: y"{name}:{port}"\n')
{'name': 'gw', 'port': 8080, 'addr': 'gw:8080'}

loads and load return plain Python. Eight of the ten types are builtins; a + block comes back as an OrderedMultimap, and a yt literal as a Template.

Templates

yt is a y-string that is not joined. Its holes resolve against the document exactly as y's do; the consumer receives the literal text and the resolved values separately, and renders them itself.

>>> d = yapyon.loads('user: "; rm -rf /"\ncmd: y"echo {user}"\ntmpl: yt"echo {user}"\n')
>>> d["cmd"]
'echo ; rm -rf /'
>>> list(d["tmpl"])
['echo ', Hole('user', '; rm -rf /'), '']

y : yt :: f-string : t-string. A joined string has lost which bytes the author wrote and which came from the data, and nothing downstream can recover it; parts keep them apart until a consumer that knows the destination — shell, SQL, HTML, a registry — decides how each value is made safe.

A hole carries .value (typed), .lexeme (the document's spelling, so 3.10 renders back as 3.10 rather than 3.1) and .ref (the reference as written). Carrying is unconstrained — a hole may hold a list or raw bytes, because yapyon is not the one rendering. render() joins canonically and reproduces exactly what the equivalent y produces; it is an explicit call, never an implicit str(), because an easy implicit join would undo the point.

Records

A yapyon record is the restricted form in which every leaf element has a literal value — no splicing, no templates, nothing deferred. It is a strict subset: every record is a valid yapyon document meaning the same thing.

>>> yapyon.loads_record('name: "gw"\nport: 8080\n')
{'name': 'gw', 'port': 8080}
>>> yapyon.is_record('addr: "{name}:80"\n')   # braces in a plain string are inert
True
>>> yapyon.loads_record('name: "gw"\naddr: y"{name}:80"\n')
Traceback (most recent call last):
yapyon.lexer.AkanError: akan: line 2, col 6: a record's leaves must all be
literals; a y-string defers its value (load with yapyon.loads for the full form)

loads_record / load_record are the whole pipeline minus the resolver, and a separate function rather than a keyword argument — the safe path should not be one typo away from the unsafe one. is_record answers the question by lexing, without loading.

This is why an implementation with no resolver can still be a conforming one: the safe subset is declared up front rather than carved out afterwards — and why the spec asks every implementation to say which of the two it provides. yapyon implements the full form, and so also loads records. (New in 0.1.0a2.)

A record also prints back out as yapyon, normalized:

$ python -m yapyon record examples/registry.ypy

Spelling becomes canonical — double quotes, minimal escapes, block containers — while every value survives exactly: 3.10 stays 3.10 rather than becoming 3.1, and b"..." is not respelled as base64. It works from the parse tree for that reason; the source spelling is gone once a value is a Python float. Comments do not survive, so this is a normalizer rather than a round-tripper. yapyon.emit is the same thing as a function. A non-record is refused at the offending prefix, with the record rule as the reason.

Limits

Resolution has two tiers (SPEC §5.3), and they are different numbers.

	Threshold	Exceeding it
Warn tier — fixed by the spec	depth 32, rendered size 1 MiB	shiran, and resolution continues
Refusal ceiling — this implementation's	depth 128, rendered size 4 MiB	akan

>>> deep = 'a0: "x"\n' + "".join(f'a{i}: y"{{a{i-1}}}"\n' for i in range(1, 41))
>>> yapyon.loads(deep, warn=print)["a40"]
shiran: line 41, col 5: a dependency chain 40 deep passes §5.3's warn threshold
(32); this document is costly to resolve and an implementation may refuse it
-- shorten the chain, or raise max_depth where it is loaded
'x'

Move the ceiling with loads(..., max_depth=…, max_size=…). The warn tier is not an argument: a consumer chooses what it will refuse, not what the format calls suspicious.

The ceiling is not optional and is deliberately finite — chained doubling is exponential, so a document of a few dozen lines can demand unbounded memory, and a resolver with no ceiling is a denial-of-service in anything that parses configuration it did not write. The spec declines to fix one ceiling for every implementation; it does not suggest having none.

Both tiers are about cost alone. A cycle or a missing target is always an akan at any depth, because it can never resolve.

From a checkout, the stages will also dump what they see:

$ pip install -e ".[dev]" && pytest -q
$ python -m yapyon lexer  examples/gateway.ypy   # token dump
$ python -m yapyon parser examples/gateway.ypy   # AST dump

Every stage writes its output to stdout and its diagnostics to stderr, and shows shirans by default — the library hides them behind warn=, but a person at a terminal asked. A shiran does not change the exit status; an akan exits 1.

References

A hole names a value. a.b is sugar for a["b"] — the bracket is the general form, and its content yields a key.

protocol: "claude"
mind:
  endpoint: "https://api"
  dialects:
    claude:
      api_uri: y"{endpoint}/v1"        # reaches its uncle by §5.2 scope
    codex:
      api_uri: y"{endpoint}/responses"
  chosen: y"{dialects[protocol].api_uri}"   # -> "https://api/v1"

Spelling	Means
{a.b}	the key b — canonical for identifiers
{a["b.c"]}	a key a dot cannot reach
{xs[0]}	a list position; brackets only, since 0 is no identifier
{d[p]}	the key stored in p, resolved in the y-string's own scope
{mm.k}	every value filed under k in a multimap, in order, as a list

{a["bar"]} where a dot would do is a shiran — legal, but say {a.bar}. Because the enclosing string's delimiter ends it, quote a key with the other mark: y"{a['b']}".

Relative references

__ROOT__ names an absolute position; __PARENT__ and __KEY__ name relative ones, so a block can refer to where it is:

store: "/cfg"
personas:
  kimi:
    id:     y"{__PARENT__.__KEY__}"              # -> "kimi"
    prompt: y"{__ROOT__.store}/{__PARENT__.__PARENT__.__KEY__}/{__PARENT__.__KEY__}.md"

The same text in every block, each resolving to its own name — without them a block cannot be renamed or moved without editing its contents. __PARENT__ repeats ({__PARENT__.__PARENT__.x}) and leads a reference; __KEY__ ends one. Bare {__KEY__} is the pair's own key, which is rarely what you want.

Serializers

A container cannot be spliced into text — there is no one text form and picking one would be guessing. Naming the encoding is how it crosses:

store:
  model: "m1"
  host: "https://api.example.com/v1"
body: y"{store.__AS_TOML__()}"

model = "m1"
host = "https://api.example.com/v1"

__AS_JSON__(), __AS_TOML__() and __AS_YAML__(), all written without a runtime dependency. Keys stay in document order, nothing is pruned, and where a format cannot carry a value faithfully the encoding is an error rather than an approximation — None in TOML, bytes anywhere, a multimap's repeated keys. YAML scalars are quoted unless nothing could misread them, so "no" and "3" survive as strings.

A serializer names the value it encodes, so it cannot name a bare anchor: {__PARENT__.__AS_JSON__()} would have to encode the string it is computing, and is akan. Reach past the anchor — {__ROOT__.blk.__AS_JSON__()} — which is the shape you want anyway.

Prefixes

Spelling	Name	Spoken	Result
b, b64	bytes literals	—	bytes
r, rb	raw	—	str, bytes
y	yapyon string	y-string	str, spliced at parse
yb	yapyon byte string	yeeb-string	bytes, spliced at parse
yt	yapyon template string	yeet-string	Template, unjoined
ry	raw yapyon string	ree-string	str, backslash literal

f"...", t"...", u"..." are errors with hints — their meaning depends on an enclosing scope, and a data file has none.

Diagnostics

shiran: (warning) → akan: (error) → yakamashiwa: (internal bug). Verbose success prints ええやん.