Support for parsing union types and custom parsing functions

Support for parsing union types and custom parsing functions: a task in LegoFlow-SWE (Harbor dataset). Currently, the participle parser does not support interface type productions. When a grammar field is an interface type (e.g., Expr ), the parser cannot automatically determine which concrete…

The task

Currently, the participle parser does not support interface type productions. When a grammar field is an interface type (e.g., `Expr`), the parser cannot automatically determine which concrete type to instantiate, leading to parse failures or the need for brittle workarounds. This makes it impossible to handle union…

Part of Lego-X/LegoFlow-SWE.