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3.2 Importing and Exporting: require and provide

Imports: require in The Racket Guide introduces require.

(require require-spec ...)

  require-spec   =   module-path     |   (only-in require-spec id-maybe-renamed ...)     |   (except-in require-spec id ...)     |   (prefix-in prefix-id require-spec)     |   (rename-in require-spec [orig-id bind-id] ...)     |   (combine-in require-spec ...)     |   (relative-in module-path require-spec ...)     |   (only-meta-in phase-level require-spec ...)     |   (only-space-in space require-spec ...)     |   (for-syntax require-spec ...)     |   (for-template require-spec ...)     |   (for-label require-spec ...)     |   (for-meta phase-level require-spec ...)     |   (for-space space require-spec ...)     |   derived-require-spec           module-path   =   root-module-path     |   (submod root-module-path submod-path-element ...)     |   (submod "." submod-path-element ...)     |   (submod ".." submod-path-element ...)           root-module-path   =   (quote id)     |   rel-string     |   (lib rel-string ...+)     |   id     |   (file string)     |   (planet id)     |   (planet string)     |   (planet rel-string         (user-string pkg-string vers)         rel-string ...)           submod-path-element   =   id     |   ".."           id-maybe-renamed   =   id     |   [orig-id bind-id]           phase-level   =   exact-integer     |   #f           space   =   id     |   #f           vers   =       |   nat     |   nat minor-vers           minor-vers   =   nat     |   (nat nat)     |   (= nat)     |   (+ nat)     |   (- nat)

A require-spec designates a particular set of identifiers to be bound in the importing context. Each identifier is mapped to a particular export of a particular module; the identifier to bind may be different from the symbolic name of the originally exported identifier. Each identifier also binds at a particular phase level and in a binding space.

No identifier can be bound multiple times in a given combination of phase level and binding space by an import, unless all of the bindings refer to the same original definition in the same module. In a module context, an identifier can be either imported or defined for a given phase level and binding space, but not both.

The syntax of require-spec can be extended via define-require-syntax, and when multiple require-specs are specified in a require, the bindings of each require-spec are visible for expanding later require-specs. The pre-defined forms (as exported by racket/base) are as follows:

Imports all exported bindings from the named module, using the export name for the local identifiers. (See below for information on module-path.) The lexical context of the module-path form determines the context of the introduced identifiers, adding a space scope for exports in a particular binding space, and in each export’s phase level.

If any identifier provided by module-path has a symbol form that is uninterned, the identifier is not imported (i.e., it is impossible to import a binding for an uninterned symbol). This restriction is intended to avoid compilation differences depending on whether a module has been saved to a file or not (see Printing Compiled Code).

(only-in require-spec id-maybe-renamed ...)

Like require-spec, but constrained to those exports for which the identifiers to bind match id-maybe-renamed: as id or as orig-id in [orig-id bind-id]. When a id-maybe-renamed has a bind-id, the lexical context of bind-id is used for the binding. If the id or orig-id of any id-maybe-renamed is not in the set that require-spec describes, a syntax error is reported.

Examples:

> tcp-listen

#<procedure:tcp-listen>

> my-accept

#<procedure:tcp-accept>

> tcp-accept

tcp-accept: undefined;

 cannot reference an identifier before its definition

  in module: top-level

Like require-spec, but omitting those imports for which ids are the identifiers to bind; if any id is not in the set that require-spec describes, a syntax error is reported.

Examples:

> tcp-accept

#<procedure:tcp-accept>

> tcp-listen

tcp-listen: undefined;

 cannot reference an identifier before its definition

  in module: top-level

Like require-spec, but adjusting each identifier to be bound by prefixing it with prefix-id. The lexical context of the prefix-id is ignored, and instead preserved from the identifiers before prefixing.

Examples:

> (require (prefix-in tcp: racket/tcp)) > tcp:tcp-accept

#<procedure:tcp-accept>

> tcp:tcp-listen

#<procedure:tcp-listen>

A syntax property with the key 'import-or-export-prefix-ranges is added to the local identifier in the expanded form of require.

Changed in version 8.9.0.5 of package base: Added the 'import-or-export-prefix-ranges syntax property.

(rename-in require-spec [orig-id bind-id] ...)

Like require-spec, but replacing the identifier to bind orig-id with bind-id. The lexical context of bind-id is used for the binding. If any orig-id is not in the set that require-spec describes, a syntax error is reported.

Examples:

> accept

#<procedure:tcp-accept>

> listen

#<procedure:tcp-listen>

The union of the require-specs. If two or more imports from the require-specs have the same identifier name but they do not refer to the same original binding, a syntax error is reported.

Examples:

Like the union of the require-specs, but each relative module path in a require-spec is treated as relative to module-path instead of the enclosing context.

The require transformer that implements relative-in sets current-require-module-path to adjust module paths in the require-specs.

Like the combination of

require-spec

s, but removing any binding that is not for

phase-level

, where

#f

for

phase-level

corresponds to the

label phase level

.

The following example imports bindings only at phase level 1, the transform phase:

> (require (only-meta-in 1 'nest)) > (desc)

2 3

> num-eggs

num-eggs: undefined;

 cannot reference an identifier before its definition

  in module: top-level

The following example imports only bindings at phase level 0, the normal phase.

Like the combination of

require-spec

s, but removing any binding that is not provided for the

binding space

identifier by

space

—

which is normally an identifier, but

#f

for

space

corresponds to the

default binding space

.

Added in version 8.2.0.3 of package base.

Like the combination of require-specs, but the bindings specified by each require-spec are shifted by phase-level. The label phase level corresponds to #f, and a shifting combination that involves #f produces #f.

Examples:

Same as (for-meta 1 require-spec ...).

Same as (for-meta -1 require-spec ...).

Same as (for-meta #f require-spec ...). If an identifier in any of the require-specs is bound at more than one phase level, a syntax error is reported.

Like the combination of require-specs, but the bindings specified by each require-spec are moved to the binding space specified by space—which is normally an identifier, but #f for space corresponds to the default binding space.

A binding is moved to the new space by removing the scope for the space originally implied by require-spec, if any, and adding the scope for space, if any.

Added in version 8.2.0.3 of package base.

See define-require-syntax for information on expanding the set of require-spec forms.

Module Paths in The Racket Guide introduces module paths.

A module-path identifies a module, either a root module or a submodule that is declared lexically within another module. A root module is identified either through a concrete name in the form of an identifier, or through an indirect name that can trigger automatic loading of the module declaration. Except for the (quote id) case below, the actual resolution of a root module path is up to the current module name resolver (see current-module-name-resolver), and the description below corresponds to the default module name resolver.

Refers to a submodule previously declared with the name id or a module previously declared interactively with the name id. When id refers to a submodule, (quote id) is equivalent to (submod "." id).

Examples:

; a module declared interactively as test: > (require 'test)

A path relative to the containing source (as determined by current-load-relative-directory or current-directory). Regardless of the current platform, rel-string is always parsed as a Unix-format relative path: / is the path delimiter (multiple adjacent /s are not allowed), .. accesses the parent directory, and . accesses the current directory. The path cannot be empty or contain a leading or trailing slash, path elements before than the last one cannot include a file suffix (i.e., a . in an element other than . or ..), and the only allowed characters are ASCII letters, ASCII digits, -, +, _, ., /, and %. Furthermore, a % is allowed only when followed by two lowercase hexadecimal digits, and the digits must form a number that is not the ASCII value of a letter, digit, -, +, or _.

The % provision is intended to support a one-to-one encoding of arbitrary strings as path elements (after UTF-8 encoding). Such encodings are not decoded to arrive at a filename, but instead preserved in the file access.

If rel-string ends with a ".ss" suffix, it is converted to a ".rkt" suffix. The compiled-load handler may reverse that conversion if a ".rkt" file does not exist and a ".ss" exists.

Examples:

; a module named "x.rkt" in the same ; directory as the enclosing module's file: > (require "x.rkt") ; a module named "x.rkt" in the parent directory ; of the enclosing module file's directory: > (require "../x.rkt")

A path to a module installed into a

collection

(see

Libraries and Collections

). The

rel-string

s in

lib

are constrained similar to the plain

rel-string

case, with the additional constraint that a

rel-string

cannot contain

.

or

..

directory indicators.

The specific interpretation of the path depends on the number and shape of the rel-strings:

• If a single rel-string is provided, and if it consists of a single element (i.e., no /) with no file suffix (i.e., no .), then rel-string names a collection, and "main.rkt" is the library file name.

  Examples:

• If a single rel-string is provided, and if it consists of multiple /-separated elements, then each element up to the last names a collection, subcollection, etc., and the last element names a file. If the last element has no file suffix, ".rkt" is added, while a ".ss" suffix is converted to ".rkt".

  Examples:

  ; "turbo.rkt" from the "swindle" collection: > (require (lib "swindle/turbo")) ; the same: > (require (lib "swindle/turbo.rkt")) ; the same: > (require (lib "swindle/turbo.ss"))

• If a single rel-string is provided, and if it consists of a single element with a file suffix (i.e, with a .), then rel-string names a file within the "mzlib" collection. A ".ss" suffix is converted to ".rkt". (This convention is for compatibility with older version of Racket.)

  Examples:

  ; "tar.rkt" module from the "mzlib" collection: > (require (lib "tar.ss"))

• Otherwise, when multiple rel-strings are provided, the first rel-string is effectively moved after the others, and all rel-strings are appended with / separators. The resulting path names a collection, then subcollection, etc., ending with a file name. No suffix is added automatically, but a ".ss" suffix is converted to ".rkt". (This convention is for compatibility with older version of Racket.)

  Examples:

  ; "tar.rkt" module from the "mzlib" collection: > (require (lib "tar.ss" "mzlib"))

A shorthand for a lib form with a single rel-string whose characters are the same as in the symbolic form of id. In addition to the constraints of a lib rel-string, id must not contain ..

Example:

Similar to the plain

rel-string

case, but

string

is a path—

possibly absolute—

using the current platform’s path conventions and

expand-user-path

. A

".ss"

suffix is converted to

".rkt"

.

Example:

(planet id)

(planet string) (planet rel-string (user-string pkg-string vers)         rel-string ...)

Specifies a library available via the PLaneT server.

The first form is a shorthand for the last one, where the id’s character sequence must match the following ‹spec› grammar:

‹spec›

 ::= 

‹owner› / ‹pkg› ‹lib›

‹owner›

 ::= 

‹elem›

‹pkg›

 ::= 

‹elem›  |  ‹elem› : ‹version›

‹version›

 ::= 

‹int›  |  ‹int› : ‹minor›

‹minor›

 ::= 

‹int›  |  <= ‹int›  |  >= ‹int›  |  = ‹int›

  |  

‹int› - ‹int›

‹lib›

 ::= 

‹empty›  |  / ‹path›

‹path›

 ::= 

‹elem›  |  ‹elem› / ‹path›

and where an ‹elem› is a non-empty sequence of characters that are ASCII letters, ASCII digits, -, +, _, or % followed by lowercase hexadecimal digits (that do not encode one of the other allowed characters), and an ‹int› is a non-empty sequence of ASCII digits. As this shorthand is expended, a ".plt" extension is added to ‹pkg›, and a ".rkt" extension is added to ‹path›; if no ‹path› is included, "main.rkt" is used in the expansion.

A (planet string) form is like a (planet id) form with the identifier converted to a string, except that the string can optionally end with a file extension (i.e., a .) for a ‹path›. A ".ss" file extension is converted to ".rkt".

In the more general last form of a planet module path, the rel-strings are similar to the lib form, except that the (user-string pkg-string vers) names a PLaneT-based package instead of a collection. A version specification can include an optional major and minor version, where the minor version can be a specific number or a constraint: (nat nat) specifies an inclusive range, (= nat) specifies an exact match, (+ nat) specifies a minimum version and is equivalent to just nat, and (- nat) specifies a maximum version. The =, +, and - identifiers in a minor-version constraint are recognized symbolically.

Examples:

; "main.rkt" in package "farm" by "mcdonald": > (require (planet mcdonald/farm)) ; "main.rkt" in version >= 2.0 of "farm" by "mcdonald": > (require (planet mcdonald/farm:2)) ; "main.rkt" in version >= 2.5 of "farm" by "mcdonald": > (require (planet mcdonald/farm:2:5)) ; "duck.rkt" in version >= 2.5 of "farm" by "mcdonald": > (require (planet mcdonald/farm:2:5/duck))

(submod root-module-path submod-path-element ...)

(submod "." submod-path-element ...) (submod ".." submod-path-element ...)

Identifies a

submodule

within the module specified by

root-module-path

or relative to the current module in the case of

(submod "." ....)

, where

(submod ".." submod-path-element ...)

is equivalent to

(submod "." ".." submod-path-element ...)

. Submodules have symbolic names, and a sequence of identifiers as

submod-path-element

s determine a path of successively nested submodules with the given names. A

".."

as a

submod-path-element

names the enclosing module of a submodule, and it’s intended for use in

(submod "." ....)

and

(submod ".." ....)

forms.

As require prepares to handle a sequence of require-specs, it logs a “prefetch” message to the current logger at the 'info level, using the name 'module-prefetch, and including message data that is a list of two elements: a list of module paths that appear to be imported, and a directory path to use for relative module paths. The logged list of module paths may be incomplete, but a compilation manager can use approximate prefetch information to start on compilations in parallel.

Changed in version 6.0.1.10 of package base: Added prefetch logging.

Examples:

#<procedure:fcontrol>

> fcontrol

fcontrol: undefined;

 cannot reference an identifier before its definition

  in module: top-level

Exports: provide in The Racket Guide introduces provide.

A provide-spec indicates one or more bindings to provide. For each exported binding, the external name is a symbol that can be different from the symbolic form of the identifier that is bound within the module. Also, each export is drawn from a particular phase level and exported at the same phase level; by default, the relevant phase level is the number of begin-for-syntax forms that enclose the provide form. Finally, each export is drawn from a binding space and exported at the same binding space.

The syntax of provide-spec can be extended by bindings to provide transformers or provide pre-transformers, such as via define-provide-syntax, but the pre-defined forms are as follows.

Exports id, which must be bound within the module (i.e., either defined or imported) at the relevant phase level and binding space. The symbolic form of id is used as the external name, and the symbolic form of the defined or imported identifier must match (otherwise, the external name could be ambiguous).

Examples:

If id has a transformer binding to a rename transformer, then the transformer affects the exported binding. See make-rename-transformer for more information.

Exports all identifiers that are defined at the relevant

phase level

within the exporting module, and that have the same lexical context as the

(all-defined-out)

form, excluding bindings to

rename transformers

where the target identifier has the

'not-provide-all-defined syntax property

. The external name for each identifier is the symbolic form of the identifier. Only identifiers accessible from the lexical context of the

(all-defined-out)

form are included; that is, macro-introduced imports are not re-exported, unless the

(all-defined-out)

form was introduced at the same time.

Examples:

Exports all identifiers that are imported into the exporting module using a

require-spec

built on each

module-path

(see

Importing and Exporting: require and provide

) with no

phase-level

shift. The symbolic name for export is derived from the name that is bound within the module, as opposed to the symbolic name of the export from each

module-path

. Only identifiers accessible from the lexical context of the

module-path

are included; that is, macro-introduced imports are not re-exported, unless the

module-path

was introduced at the same time.

Examples:

> (require 'hen-house) > num-eggs

2

Exports each

orig-id

, which must be

bound

within the module at the relevant

phase level

and

binding space

. The symbolic name for each export is

export-id

instead of

orig-id

.

Examples:

> (require 'nest) > num-eggs

2

> count

count: undefined;

 cannot reference an identifier before its definition

  in module: top-level

Like the first provide-spec, but omitting the bindings listed in each subsequent provide-spec. If one of the latter bindings is not included in the initial provide-spec, a syntax error is reported. The symbolic export name information in the latter provide-specs is ignored; only the bindings are used.

Examples:

> (require 'nest) > num-eggs

2

> num-chicks

num-chicks: undefined;

 cannot reference an identifier before its definition

  in module: top-level

Like provide-spec, but with each symbolic export name from provide-spec prefixed with prefix-id.

Examples:

> (require 'nest) > chicken:num-eggs

2

A syntax property with the key 'import-or-export-prefix-ranges is added to the exported identifier in the expanded form of provide.

Changed in version 8.9.0.5 of package base: Added the 'import-or-export-prefix-ranges syntax property.

Exports the bindings associated with a structure type

id

. Typically,

id

is bound with

(struct id ....)

; more generally,

id

must have a

transformer

binding of structure-type information at the relevant

phase level

; see

Structure Type Transformer Binding

. Furthermore, for each identifier mentioned in the structure-type information, the enclosing module must define or import one identifier that is

free-identifier=?

. If the structure-type information includes a super-type identifier, and if the identifier has a

transformer

binding of structure-type information, the accessor and mutator bindings of the super-type are

not

included by

struct-out

for export.

Examples:

> (require 'nest) > (egg-color (egg 'blue 10))

'blue

The union of the provide-specs.

Examples:

> (require 'nest) > num-eggs

2

> num-chicks

1

Like the union of the

provide-spec

s, except that the exports are

protected

: requiring modules may refer to these bindings, but may not extract these bindings from macro expansions or access them via

eval

without access privileges. For more details, see

Code Inspectors

. The

provide-spec

must specify only bindings that are defined within the exporting module.

Examples:

> (define weak-inspector (make-inspector (current-code-inspector))) > (require 'nest) > (list num-eggs num-chicks)

'(2 3)

> (weak-eval 'num-eggs)

2

> (weak-eval 'num-chicks)

?: access disallowed by code inspector to protected variable

  from module: 'nest

  at: num-chicks

See also Code Inspectors for Trusted and Untrusted Code.

Like the union of the provide-specs, but adjusted to apply to the phase level specified by phase-level relative to the current phase level (where #f corresponds to the label phase level). In particular, an id or rename-out form as a provide-spec refers to a binding at phase-level relative to the current level, an all-defined-out exports only definitions at phase-level relative to the current phase level, and an all-from-out exports bindings imported with a shift by phase-level.

Examples:

> (require 'nest) > (test-eggs)

Eggs are 2

0

> chickens

3

eval:7:0: provide: provided identifier is not defined or

required

  at: eggs

  in: (provide (for-syntax eggs) chickens)

Eggs are 2

> (test)

0

Same as (for-meta 1 provide-spec ...).

Same as (for-meta -1 provide-spec ...).

Same as (for-meta #f provide-spec ...).

Like the union of the provide-specs, but adjusted to apply to the binding space specified by space—where space is either an identifier or #f for the default binding space. In particular, an id or rename-out form as a provide-spec refers to a binding in space, an all-defined-out exports only definitions in space, and an all-from-out exports bindings imported into space.

When providing a binding for a non-default binding space, normally a module should also provide a binding for the default binding space, where the default-space binding represents the intended meaning of the identifier. When a module later imports the same name in different spaces from modules that adhere to this convention, then if the two modules also (re)export the same binding for the name in the default space, the imports are likely consistent. If the two modules export different bindings for the name in the default space, then attempting to import both modules will trigger an error about conflicting imports, and a programmer can explicitly resolve the mismatch.

Added in version 8.2.0.3 of package base.

See define-provide-syntax for information on expanding the set of provide-spec forms.

Each export specified within a module must have a distinct symbolic export name, though the same binding can be specified with the multiple symbolic names.

(#%require raw-require-spec ...)

  raw-require-spec   =   phaseless-spec     |   (for-meta phase-level raw-require-spec ...)     |   (for-syntax raw-require-spec ...)     |   (for-template raw-require-spec ...)     |   (for-label raw-require-spec ...)     |   (just-meta phase-level raw-require-spec ...)     |   (portal portal-id content)           phase-level   =   exact-integer     |   #f           phaseless-spec   =   spaceless-spec     |   (for-space space phaseless-spec ...)     |   (just-space space spaceless-spec ...)           space   =   id     |   #f           spaceless-spec   =   raw-module-path     |   (only raw-module-path id ...)     |   (prefix prefix-id raw-module-path)     |   (all-except raw-module-path id ...)     |   (prefix-all-except prefix-id                    raw-module-path id ...)     |   (rename raw-module-path local-id exported-id)           raw-module-path   =   raw-root-module-path     |   (submod raw-root-module-path id ...+)     |   (submod "." id ...+)           raw-root-module-path   =   (quote id)     |   rel-string     |   (lib rel-string ...)     |   id     |   (file string)     |   (planet rel-string         (user-string pkg-string vers ...))     |   literal-path

The primitive import form, to which

expands. A

is similar to a

in a

form, except that the syntax is more constrained, not composable, and not extensible. Also, sub-form names like

and

are recognized symbolically, instead of via bindings. Some nested constraints are not formalized in the grammar above:

• a just-meta form cannot appear within a just-meta form;

• a for-meta, for-syntax, for-template, or for-label form cannot appear within a for-meta, for-syntax, for-template, or for-label form; and

• a for-space form cannot appear within a for-space form.

• a portal form cannot appear within a just-meta form.

Except for the portal form, each raw-require-spec corresponds to the obvious require-spec, but the rename sub-form has the identifiers in reverse order compared to rename-in.

For most raw-require-specs, the lexical context of the raw-require-spec determines the context of introduced identifiers. The exception is the rename sub-form, where the lexical context of the local-id is preserved.

A literal-path as a raw-root-module-path corresponds to a path in the sense of path?. Since path values are never produced by read-syntax, they appear only in programmatically constructed expressions. They also appear naturally as arguments to functions such as namespace-require, with otherwise take a quoted raw-module-spec.

The portal form provides a way to define portal syntax at any phase level. A (portal portal-id content), defines portal-id to portal syntax with content effectively quoted to serve as its content.

Changed in version 8.2.0.3 of package base: Added for-space and just-space.
Changed in version 8.3.0.8: Added portal.

(#%provide raw-provide-spec ...)

  raw-provide-spec   =   phaseless-spec     |   (for-meta phase-level phaseless-spec ...)     |   (for-syntax phaseless-spec ...)     |   (for-label phaseless-spec ...)     |   (protect raw-provide-spec ...)           phase-level   =   exact-integer     |   #f           phaseless-spec   =   spaceless-spec     |   (for-space space spaceless-spec ...)     |   (protect phaseless-spec ...)           space   =   id     |   #f           spaceless-spec   =   id     |   (rename local-id export-id)     |   (struct struct-id (field-id ...))     |   (all-from raw-module-path)     |   (all-from-except raw-module-path id ...)     |   (all-defined)     |   (all-defined-except id ...)     |   (prefix-all-defined prefix-id)     |   (prefix-all-defined-except prefix-id id ...)     |   (protect spaceless-spec ...)     |   (expand (id . datum))     |   (expand (id . datum) orig-form)

The primitive export form, to which

expands. A

is as for

. A

sub-form cannot appear within a

sub-form.

Like #%require, the sub-form keywords for #%provide are recognized symbolically, and nearly every raw-provide-spec has an obvious equivalent provide-spec via provide, with the exception of the struct and expand sub-forms.

A (struct struct-id (field-id ...)) sub-form expands to struct-id, make-struct-id, struct:struct-id, struct-id?, struct-id-field-id for each field-id, and set-struct-id-field-id! for each field-id. The lexical context of the struct-id is used for all generated identifiers.

Unlike #%require, the #%provide form is macro-extensible via an explicit expand sub-form; the (id . datum) part is locally expanded as an expression (even though it is not actually an expression), stopping when a begin form is produced; if the expansion result is (begin raw-provide-spec ...), it is spliced in place of the expand form, otherwise a syntax error is reported. If an orig-form part is provided, then it is used instead of the #%provide form when raising syntax errors, such as a “provide identifier is not defined” error. The expand sub-form is not normally used directly; it provides a hook for implementing provide and provide transformers.

The all-from and all-from-except forms re-export only identifiers that are accessible in lexical context of the all-from or all-from-except form itself. That is, macro-introduced imports are not re-exported, unless the all-from or all-from-except form was introduced at the same time. Similarly, all-defined and its variants export only definitions accessible from the lexical context of the spaceless-spec form.

Changed in version 8.2.0.3 of package base: Added for-space.
Changed in version 8.2.0.5: Added orig-form support to expand.

The following forms support more complex selection and manipulation of sets of imported identifiers.

Like

, but including only imports whose names match

. The

must be a literal regular expression (see

).

Examples:

> (require racket/require) > (require (matching-identifiers-in #rx"\\w*fish" 'zoo)) > tunafish

1

> swordfish

2

> blowfish

3

> monkey

monkey: undefined;

 cannot reference an identifier before its definition

  in module: top-level

Like require-spec, but omitting those imports that would be imported by one of the subtracted-specs.

Examples:

> (require racket/require) > (require (subtract-in 'solar-system 'earth)) > land

land: undefined;

 cannot reference an identifier before its definition

  in module: top-level

> aliens

4

Applies an arbitrary transformation on the import names (as strings) of require-spec. The proc-expr must evaluate at expansion time to a single-argument procedure, which is applied on each of the names from require-spec. For each name, the procedure must return either a string for the import’s new name or #f to exclude the import.

The second part of filtered-in is expand-time code evaluated in the scope of the enclosing module. Accordingly, most uses need (require (for-syntax racket/base)) if racket/base is not already imported for-syntax. For example, #lang racket establishes this import automatically, while #lang racket/base does not.

For example,

imports only bindings from

that match the pattern

, and it converts the names to “camel case.”

Specifies paths to modules named by the rel-strings similar to using the rel-strings directly, except that if a required module file is not found relative to the enclosing source, it is searched for in the parent directory, and then in the grand-parent directory, etc., all the way to the root directory. The discovered path relative to the enclosing source becomes part of the expanded form.

This form is useful in setting up a “project environment.” For example, using the following "config.rkt" file in the root directory of your project:

and using "utils/in-here.rkt" under the same root directory:

then

works for any other module under the project directory to find

:

Note that the order of requires in the example is important, as each of the first two bind the identifier used in the following.

An alternative in this scenario is to use

directly to find the utility module:

but then sub-directories that are called "utils" override the one in the project’s root. In other words, the previous method requires only a single unique name.

(multi-in subs ...+)

  subs   =   sub-path     |   (sub-path ...)           sub-path   =   rel-string     |   id

Specifies multiple files to be required from a hierarchy of directories or collections. The set of required module paths is computed as the Cartesian product of the

groups, where each

is combined with other

s in order using a

separator. A

as a

is equivalent to

. All

s in a given

form must be either strings or identifiers.

Examples:

(require (multi-in racket (dict list)))

   is equivalent to 

(require (multi-in "math" "matrix" "utils.rkt"))

   is equivalent to 

(require (multi-in "utils" ("math.rkt" "matrix.rkt")))

   is equivalent to 

(require (multi-in ("math" "matrix") "utils.rkt"))

   is equivalent to 

(require (multi-in ("math" "matrix") ("utils.rkt" "helpers.rkt")))

   is equivalent to 

Like

, but including only exports of bindings with an external name that matches

. The

must be a literal regular expression (see

).

Analogous to

, but for filtering and renaming exports.

See the documentation of filtered-in for use with #lang racket/base.

For example,

exports only bindings that match the pattern #rx"^[a-z-]+$", and it converts the names to “camel case.”

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