On this page:

2.5 Variable References and #%top

Refers to a module-level or local binding, when id is not bound as a transformer (see Expansion (Parsing)). At run-time, the reference evaluates to the value in the location associated with the binding.

When the expander encounters an id that is not bound by a module-level or local binding, it converts the expression to (#%top . id) giving #%top the lexical context of the id; typically, that context refers to #%top. See also Expansion Steps.


  > (define x 10)
  > x


  > (let ([x 5]) x)


  > ((lambda (x) x) 2)


(#%top . id)
Refers to a top-level definition that could bind id, even if id has a local binding in its context. Such references are disallowed anywhere within a module form. See also Expansion Steps for information on how the expander introduces #%top identifiers.


  > (define x 12)
  > (let ([x 5]) (#%top . x))