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Mountainash Core

An intelligent textbook for the mountainash cross-backend data expression and relational pipeline library.

Transitional publishing: This manual remains on the central site until its per-repository cutover.

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Chapters

  1. Foundation Concepts
  2. Core Infrastructure
  3. Expression API Basics
  4. Expression Namespaces and Functions
  5. Expression Operations
  6. Expression AST and Function Keys
  7. Expression Function Registry and Compilation
  8. Expression Backends
  9. Type System and Schema
  10. Relation API Core Operations
  11. Relation API Advanced Features
  12. Pipeline Framework
  13. DAG and DataPackage
  14. Relation AST and System Architecture
  15. Relation Backends

Key Topics

  • Expression system -- fluent expression API with AST nodes, function key registry, and visitor pattern compilation across Polars, Narwhals, and Ibis backends
  • Relation system -- relational AST with Substrait-aligned node types, a fluent relation builder, and unified visitor for backend-portable query construction
  • Type system (TypeSpec) -- universal type metadata aligned with Frictionless Table Schema for schema extraction, validation, and cross-backend conformance
  • Pipeline framework -- declarative multi-step pipelines with typed parameter binding, caching, and DAG orchestration via RelationDAG and Frictionless DataPackage
  • Ternary logic -- three-valued semantics (TRUE/FALSE/UNKNOWN) with sentinel integers and auto-booleanization for null-safe expression evaluation