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Concepts

Core Concepts

FHIRPath is a path-based navigation and extraction language designed for use with FHIR® resources. Before diving into advanced usage, it is important to understand the core concepts that govern how expressions are evaluated.

This section covers:

  • Type System – The eight primitive types (Boolean, Integer, Decimal, String, Date, DateTime, Time, Quantity), their Go representations, and the Value, Comparable, and Numeric interfaces.

  • Collections – How FHIRPath represents all results as ordered collections, the rules for empty propagation (three-valued logic), singleton evaluation, and the full set of collection operations.

  • Operators – Arithmetic, comparison, equality, equivalence, Boolean, collection, and type operators, including precedence rules and three-valued truth tables.

  • Environment Variables – Built-in variables (%resource, %context, %ucum) and how to define custom variables with WithVariable().

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