3.23 Blocks: block

The Racket Reference

3 Syntactic Forms

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

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3.23Blocks: block 🔗 i

(require racket/block ) 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 (fx)
(block
(define y(add1 x))
(displayln y)
(define z(* 2y))
(+ 3z)))
> (f12)

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