Semantic Prefix Oracles for LLM Decoding: Contracts and Differential Validation
Constrained decoding can enforce regular or context-free output formats, but many program-generation failures are semantic: scope, typing, and declaration effects depend on context. We present semantic grammar specifications, a declarative formalism that attaches such constraints to a context-free surface and executes them during Earley descent. Our implementation enforces \emph{safe pruning}: it rejects only prefixes whose semantic contradictions cannot be repaired by any continuation. A separate, grammar-dependent, \emph{dead-end freedom} property guarantees the existence of a realizable witness for each remaining branch. We give simple sufficient conditions based on surface productivit...
| Authors | Paul Kronlund-Drouault |
|---|---|
| Primary category | cs.PL |
| Published | 28 September 2026 |
| Last updated at source | 28 September 2026 |
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