Teckel Parser (teckel-rs)

teckel-rs is the Rust implementation of the Teckel Specification v3.0 parser. It takes YAML pipeline definitions and produces a fully validated, typed domain model ready for execution by a downstream engine.

The project is split into two crates:

Crate	Purpose
teckel-model	Pure domain types — Source, Asset, Pipeline, TeckelDataType, error codes. Minimal dependencies (serde, thiserror).
teckel-parser	YAML deserialization, variable substitution, secret resolution, config merging, rewrite to domain model, and semantic validation (V-001 through V-008).

Quick start

Add the parser crate to your project:

cargo add teckel-parser

Parse a Teckel YAML document:

use std::collections::BTreeMap;
use teckel_parser::parse;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let yaml = r#"
version: "3.0"
input:
  - name: employees
    format: csv
    path: "data/employees.csv"
    options:
      header: true

transformation:
  - name: filtered
    where:
      from: employees
      filter: "salary > 50000"

output:
  - name: filtered
    format: parquet
    path: "output/employees"
    mode: overwrite
"#;

    let variables = BTreeMap::new();
    let pipeline = parse(yaml, &variables)?;

    println!("Parsed {} assets", pipeline.context.len());
    for (name, asset) in &pipeline.context {
        println!("  {} -> {:?} deps", name, asset.source.dependencies().len());
    }

    Ok(())
}

What the parser does

The parse() function runs an 8-step pipeline:

1. Variable substitution -- resolves ${VAR:default} placeholders
2. Secret resolution -- resolves {{secrets.alias}} via the SecretsProvider trait
3. YAML parsing -- deserializes into serde structs
4. Version validation -- ensures version is "2.0" or "3.0"
5. Rewrite -- converts the YAML model into the domain model (Pipeline)
6. Semantic validation -- runs V-001 through V-008 checks
7. Expression validation -- optionally parses all expression strings
8. Tag propagation -- inherits tags through the DAG

The result is a Pipeline containing a Context (a BTreeMap<AssetRef, Asset>) with every input, transformation, and output as a typed node in the pipeline DAG.

Specification

This parser implements the Teckel Specification v3.0. The spec defines the YAML schema, all 45 transformation types, the expression language, data quality suites, metadata, and error codes.

Source code

The full source is available on GitHub.