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.

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

top← prev up next →

1	Language Model
2	Syntactic Forms
3	Datatypes
4	Structures
5	Classes and Objects
6	Units
7	Contracts
8	Pattern Matching
9	Control Flow
10	Concurrency and Parallelism
11	Macros
12	Input and Output
13	Reflection and Security
14	Operating System
15	Memory Management
16	Unsafe Operations
17	Running Racket
	Bibliography
	Index

2.1	Modules: module, ...
2.2	Importing and Exporting: require and provide
2.3	Literals: quote and #%datum
2.4	Expression Wrapper: #%expression
2.5	Variable References and #%top
2.6	Locations: #%variable-reference
2.7	Procedure Applications and #%app
2.8	Procedure Expressions: lambda and case-lambda
2.9	Local Binding: let, let*, letrec, ...
2.10	Local Definitions: local
2.11	Constructing Graphs: shared
2.12	Conditionals: if, cond, and, and or
2.13	Dispatch: case
2.14	Definitions: define, define-syntax, ...
2.15	Sequencing: begin, begin0, and begin-for-syntax
2.16	Guarded Evaluation: when and unless
2.17	Assignment: set! and set!-values
2.18	Iterations and Comprehensions: for, for/ list, ...
2.19	Continuation Marks: with-continuation-mark
2.20	Quasiquoting: quasiquote, unquote, and unquote-splicing
2.21	Syntax Quoting: quote-syntax
2.22	Interaction Wrapper: #%top-interaction
2.23	Limiting Scope: define-package, open-package, ...
2.24	Blocks: block
2.25	Internal-Definition Limiting: #%stratified-body