Normative Rules: Unbound-Variable Reference

Evaluating a symbol with no active dynamic binding and no namespace binding yields nil rather than signalling an error. Referencing a never-set name is therefore not directly observable; the typical surface symptom is a downstream type error when nil is passed to an arithmetic or other type-checking primitive.

This contrasts with both Common Lisp (unbound-variable is a condition) and R7RS Scheme (the result is an error). The silent-NIL behaviour is strict across every supported AutoLISP host: there is no language-level way for portable AutoLISP source to distinguish "bound to nil" from "never bound" at reference time, and boundp — the only predicate exposed for that question — additionally creates the symbol and binds it to nil as a side effect of being asked (chapter 7, BOUNDP entry). Programmer-visible state therefore collapses every never-set name into a nil-bound name on first observation.

The consequence: there is no compliant AutoLISP dialect in which a bare reference to an unset symbol can signal an error without breaking deployed code. Strict mode in this specification means common to every conforming AutoLISP runtime, not the most pedantic; silent-NIL is therefore the strict rule.

• (setq y (+ never-set-symbol 1)) does not signal unbound variable; it signals bad argument type <NIL>; expected <NUMBER> at [+].
• (boundp 'never-set) returns nil but additionally creates the symbol and binds it to nil (chapter 7, BOUNDP). After this call never-set is observably nil-bound.
• A program cannot reliably detect "never assigned" once any code path has either referenced or boundp-tested the name.

BricsCAD V26 / macOS direct probe section C — every closure test that referenced an out-of-extent local surfaced its error at the consuming primitive (+), not at the variable reference. The error message wrapped the value <NIL>, which is the expected payload after the silent-NIL evaluation.

Silent-NIL on unbound reference is strict across the strict, autocad-2026, and bricscad-v26 dialects. clautolisp exposes a non-conforming diagnostic knob, unbound-variable-mode :strict-error, that programs can opt into through a custom-built dialect descriptor; doing so produces source code that does not run on any real AutoLISP host and is intended only for static-analysis tooling and unit tests.

• Function Entry: BOUNDP (chapter 7) — the only language-level distinction between bound-to-nil and unbound, with its documented binding side effect.

• Phase-6 BricsCAD V26 / macOS semantics probe section C (indirect evidence; explicit probe pending due to launch-flake on this run).