3.17 Assignment: set! and set!-values

3.17 Assignment: set! and set!-values🔗ℹ

Assignment: set! in The Racket Guide introduces set!.

syntax
(set! id expr)

If id has a transformer binding to an assignment transformer, as produced by make-set!-transformer or as an instance of a structure type with the prop:set!-transformer property, then this form is expanded by calling the assignment transformer with the full expressions. If id has a transformer binding to a rename transformer as produced by make-rename-transformer or as an instance of a structure type with the prop:rename-transformer property, then this form is expanded by replacing id with the target identifier (e.g., the one provided to make-rename-transformer). If a transformer binding has both prop:set!-transformer and prop:rename-transformer properties, the latter takes precedence.

Otherwise, evaluates expr and installs the result into the location for id, which must be bound as a local variable or defined as a top-level variable or module-level variable. If id refers to an imported binding, a syntax error is reported. If id refers to a top-level variable that has not been defined, the exn:fail:contract exception is raised.

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