3.5 Variable References and #%top

syntax
id

Refers to a top-level, module-level, or local binding, when id is not bound as a transformer (see Expansion). 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

syntax
(#%top . id)

Equivalent to id when id is bound to a module-level or top-level variable. In a top-level context, (#%top . id) always refers to a top-level variable, even if id is unbound or bound to syntax, as long as id does not have a local binding. In all contexts, (#%top . id) is a syntax error if id has a local binding.

Within a module form, (#%top . id) expands to just id as long as id is defined within the module and has no local binding in its context. At phase level 0, (#%top . id) is an immediate syntax error if id is not bound. At phase level 1 and higher, a syntax error is reported if id is not defined at the corresponding phase by the end of module-body partial expansion.

See also Expansion Steps for information on how the expander introduces #%top identifiers.

Examples:

> (define x 12)
> (#%top . x)
12

Changed in version 6.3 of package base: Changed the introduction of #%top in a top-level context to unbound identifiers only.
Changed in version 8.2.0.7: Changed treatment of locally bound id to always report a syntax error, even outside of a module.

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

3.1	Modules: module, module*, ...
3.2	Importing and Exporting: require and provide
3.3	Literals: quote and #%datum
3.4	Expression Wrapper: #%expression
3.5	Variable References and #%top
3.6	Locations: #%variable-reference
3.7	Procedure Applications and #%app
3.8	Procedure Expressions: lambda and case-lambda
3.9	Local Binding: let, let*, letrec, ...
3.10	Local Definitions: local
3.11	Constructing Graphs: shared
3.12	Conditionals: if, cond, and, and or
3.13	Dispatch: case
3.14	Definitions: define, define-syntax, ...
3.15	Sequencing: begin, begin0, and begin-for-syntax
3.16	Guarded Evaluation: when and unless
3.17	Assignment: set! and set!-values
3.18	Iterations and Comprehensions: for, for/ list, ...
3.19	Continuation Marks: with-continuation-mark
3.20	Quasiquoting: quasiquote, unquote, and unquote-splicing
3.21	Syntax Quoting: quote-syntax
3.22	Interaction Wrapper: #%top-interaction
3.23	Blocks: block
3.24	Internal-Definition Limiting: #%stratified-body
3.25	Performance Hints: begin-encourage-inline
3.26	Importing Modules Lazily: lazy-require