► |  | The Racket Reference

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

▼ | 6 | Units

6.1 | Creating Units
6.2 | Invoking Units
6.3 | Linking Units and Creating Compound Units
6.4 | Inferred Linking
6.5 | Generating A Unit from Context
6.6 | Structural Matching
6.7 | Extending the Syntax of Signatures
6.8 | Unit Utilities
6.9 | Unit Contracts
6.10 | Single-Unit Modules
6.11 | Single-Signature Modules
6.12 | Transformer Helpers

On this page:

invoke-unit
define-values/ invoke-unit

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#### 6.2`` Invoking Units

> syntax (invoke-unit unit-expr)
> (invoke-unit unit-expr (import tagged-sig-spec ...))

Invokes the unit produced by unit-expr. For each of the unit’s imports, the invoke-unit expression must contain a tagged-sig-spec in the import clause; see unit for the grammar of tagged-sig-spec. If the unit has no imports, the import clause can be omitted.

When no tagged-sig-specs are provided, unit-expr must produce a unit that expects no imports. To invoke the unit, all bindings are first initialized to the #<undefined> value. Next, the unit’s body definitions and expressions are evaluated in order; in the case of a definition, evaluation sets the value of the corresponding variable(s). Finally, the result of the last expression in the unit is the result of the invoke-unit expression.

Each supplied tagged-sig-spec takes bindings from the surrounding context and turns them into imports for the invoked unit. The unit need not declare an import for every provided tagged-sig-spec, but one tagged-sig-spec must be provided for each declared import of the unit. For each variable identifier in each provided tagged-sig-spec, the value of the identifier’s binding in the surrounding context is used for the corresponding import in the invoked unit.

> > syntax
> > (define-values/invoke-unit unit-expr
> > (import tagged-sig-spec ...)
> > (export tagged-sig-spec ...))

Like invoke-unit, but the values of the unit’s exports are copied to new bindings.

The unit produced by unit-expr is linked and invoked as for invoke-unit. In addition, the export clause is treated as a kind of import into the local definition context. That is, for every binding that would be available in a unit that used the export clause’s tagged-sig-spec as an import, a definition is generated for the context of the define-values/invoke-unit form.

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