Achieving healthcare interoperability requires robust data querying standards like FHIR and FHIRPath. This article details the creation of 'gofhir', a complete FHIRPath query engine implementation in Golang. It explains how to parse complex medical data expressions using ANTLR, manage a strict type system for clinical resources, and evaluate queries using the visitor pattern.

The library addresses critical challenges such as precise decimal arithmetic, collection-based logic, and concurrency safety. Understanding this implementation is vital for developers building high-performance health integration platforms that require precise extraction and validation of patient data from FHIR JSON resources.