2.5 Variable References and #%top
| id |
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.
Examples: |
| > (define x 10) |
| > x |
10 |
| > (let ([x 5]) x) |
5 |
| > ((lambda (x) x) 2) |
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.
Examples: |
| > (define x 12) |
| > (let ([x 5]) (#%top . x)) |
12 |