► |  | Guide: PLT Scheme

1 | Welcome to PLT Scheme
2 | Scheme Essentials
3 | Built-In Datatypes
4 | Expressions and Definitions
5 | Programmer-Defined Datatypes
6 | Modules
7 | Contracts
8 | Input and Output
9 | Regular Expressions
10 | Exceptions and Control
11 | Iterations and Comprehensions
12 | Pattern Matching
13 | Classes and Objects
14 | Units (Components)
15 | Reflection and Dynamic Evaluation
16 | Macros
17 | Performance
18 | Running and Creating Executables
19 | Compilation and Configuration
20 | More Libraries
21 | Dialects of Scheme
| Bibliography
| Index

▼ | 6 | Modules

6.1 | Module Basics
6.2 | Module Syntax
6.3 | Module Paths
6.4 | Imports: require
6.5 | Exports: provide
6.6 | Assignment and Redefinition

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#### 6.5`` Exports: provide

By default, all of a module’s definitions are private to the module. The provide form specifies definitions to be made available where the module is required.

> (provide provide-spec ...)

A provide form can only appear at module level (i.e., in the immediate body of a module). Specifying multiple provide-specs in a single provide is exactly the same as using multiple provides each with a single provide-spec.

Each identifier can be exported at most once from a module across all provides within the module. More precisely, the external name for each export must be distinct; the same internal binding can be exported multiple times with different external names.

The allowed shape of a provide-spec is defined recursively:

> > identifier

> > In its simplest form, a provide-spec indicates a binding within its module to be exported. The binding can be from either a local definition, or from an import.

> > (rename-out [orig-id export-id] ...)

> > A rename-out form is similar to just specifying an identifier, but the exported binding orig-id is given a different name, export-id, to importing modules.

> > (struct-out struct-id)

> > A struct-out form exports the bindings created by (define-struct struct-id ....).

> > > > > See Programmer-Defined Datatypes for information on define-struct.

> > (all-defined-out)

> > The all-defined-out shorthand exports all bindings that are defined within the exporting module (as opposed to imported).

> > Use of the all-defined-out shorthand is generally discouraged, because it makes less clear the actual exports for a module, and because PLT Scheme programmers get into the habit of thinking that definitions can be added freely to a module without affecting its public interface (which is not the case when all-defined-out is used).

> > (all-from-out module-path)

> > The all-from-out shorthand exports all bindings in the module that were imported using a require-spec that is based on module-path.

> > Although different module-paths could refer to the same file-based module, re-exporting with all-from-out is based specifically on the module-path reference, and not the module that is actually referenced.

> > (except-out provide-spec id ...)

> > Like provide-spec, but omitting the export of each id, where id is the external name of the binding to omit.

> > (prefix-out prefix-id provide-spec)

> > Like provide-spec, but adding prefix-id to the beginning of the external name for each exported binding.

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