3.23 Blocks: block

3.23 Blocks: block🔗ℹ

package: base

The bindings documented in this section are provided by the racket/block library, not racket/base or racket.

syntax
(block defn-or-expr ...)

Supports a mixture of expressions and mutually recursive definitions, as in a module body. Unlike an internal-definition context, the last defn-or-expr need not be an expression.

The result of the block form is the result of the last defn-or-expr if it is an expression, #<void> otherwise. If no defn-or-expr is provided (after flattening begin forms), the result is #<void>.

The final defn-or-expr is executed in tail position, if it is an expression.

Examples:

> (define (f x)
    (block
      (define y (add1 x))
      (displayln y)
      (define z (* 2 y))
      (+ 3 z)))
> (f 12)
13
29

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