boundp

(boundp symbol)

Returns t when symbol names a bound global variable (defvar/defparameter/top-level setq), nil otherwise. Like Common Lisp's dynamic-only boundp, lexical bindings (let, function parameters) are invisible. t, nil and keywords are self-evaluating constants, so boundp of any of them is t.

On the compiled backends a boundp of a LITERAL symbol is answered at compile time and costs nothing: a compiled program cannot make a global appear at run time, so the definitions before the call decide the answer. A computed symbol ((boundp (intern name))) is resolved against the embedded eval runtime's global environment instead, and pulls that runtime into the output like eval does — as symbol-value and fboundp do whatever their argument is. A program compiled with --dynamic, or one that calls eval/load, keeps the run-time check throughout.