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I used to build strict systems. I defined rigid schemas. I enforced hard types. I built walls around my data to keep it clean.
This was good engineering for today. It was fatal engineering for tomorrow.
The future is an unknown data type. It arrives unannounced. A rigid system encounters the unknown and breaks. It sees a field it does not recognize. It throws an exception. The pipeline halts.
This is the fragility of arrogance. It assumes the current version is the final version. It assumes we know everything.
I refused to make that assumption.
I wrote a specific rule into the YON specification. When the parser encounters a record it does not understand, it must not crash. It must not discard. It must preserve.
The unknown tag is read. It is stored in the Abstract Syntax Tree. It is kept safe. When the document is written back out, the unknown tag remains. It survives the roundtrip.
This is forward compatibility. A v1.0 parser can process a v2.0 document. It cannot execute the new features. It cannot reason about the new logic. But it does not destroy them. It allows the future to pass through the present unharmed.
This is an application of Postel's Law. Be conservative in what you do. Be liberal in what you accept. But I refine this further. It is not just about accepting malformed input. It is about respecting valid input that I do not yet possess the vocabulary to understand.
Consider a distributed system. An agent running v2.0 emits a @SIGNAL record. An observer running v1.0 receives the stream.
In a brittle system, the v1.0 observer crashes. The tag is undefined in its schema. The connection dies.
In YON, the v1.0 observer parses the line. It sees . It checks its profile. It does not support signaling. It marks the record as structural data. It passes it downstream. The data flows. The system holds.
@SIGNALThe parser acts as a vessel. It carries the data it understands. It carries the data it does not. It does not presume that its ignorance makes the data invalid.
The implementation is clean. The parser distinguishes between syntax and semantics.
Syntax is the shape. The @TAG marker. The pipe separator. The key-value pairs. This is immutable. If the syntax is wrong, the line is corrupt.
Semantics is the meaning. What does @THOUGHT mean? What does @TENET enforce? This evolves.
A YON parser validates syntax strictly. It validates semantics loosely. If it sees a valid record with an unknown tag, it creates a generic record node in the AST. It preserves the tag name. It preserves the fields. It preserves the position.
It does not execute. It does not validate constraints. It simply holds.
I build systems to last. Over a horizon of ten or fifty years, the specification will change. The vocabulary of intelligence will grow.
If every change requires a synchronized global update, the system will fail. There will always be a mix of versions. There will always be old talking to new.
The unknown tag rule ensures they can converse. It allows the ecosystem to upgrade gradually. It prevents the hard break.
I built the parser to be humble. I taught it to hold what it does not know.
The unknown is not an error. It is simply data I have not yet learned to read.
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