11.5 Syntax Parameters

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

Binds id as syntax to a syntax parameter. The expr is an expression in the transformer environment that serves as the default value for the syntax parameter. The value is typically obtained by a transformer using syntax-parameter-value.

The id can be used with syntax-parameterize or syntax-parameter-value (in a transformer). If expr produces a procedure of one argument or a make-set!-transformer result, then id can be used as a macro. If expr produces a rename-transformer result, then id can be used as a macro that expands to a use of the target identifier, but syntax-local-value of id does not produce the target’s value.

(syntax-parameterize ((id expr) ...) body-expr ...+)

See also splicing-syntax-parameterize.

Each id must be bound to a syntax parameter using define-syntax-parameter. Each expr is an expression in the transformer environment. During the expansion of the body-exprs, the value of each expr is bound to the corresponding id.

If an expr produces a procedure of one argument or a make-set!-transformer result, then its id can be used as a macro during the expansion of the body-exprs. If expr produces a rename-transformer result, then id can be used as a macro that expands to a use of the target identifier, but syntax-local-value of id does not produce the target’s value.

11.5.1 Syntax Parameter Inspection

(require racket/stxparam-exptime)

(syntax-parameter-value id-stx) → any

id-stx : syntax?

This procedure is intended for use in a transformer environment, where id-stx is an identifier bound in the normal environment to a syntax parameter. The result is the current value of the syntax parameter, as adjusted by syntax-parameterize form.

This binding is provided for-syntax by racket/stxparam, since it is normally used in a transformer. It is provided normally by racket/stxparam-exptime.

(make-parameter-rename-transformer id-stx) → any

id-stx : syntax?

This procedure is intended for use in a transformer, where id-stx is an identifier bound to a syntax parameter. The result is a transformer that behaves as id-stx, but that cannot be used with syntax-parameterize or syntax-parameter-value.

Using make-parameter-rename-transformer is analogous to defining a procedure that calls a parameter. Such a procedure can be exported to others to allow access to the parameter value, but not to change the parameter value. Similarly, make-parameter-rename-transformer allows a syntax parameter to be used as a macro, but not changed.

The result of make-parameter-rename-transformer is not treated specially by syntax-local-value, unlike the result of make-rename-transformer.

This binding is provided for-syntax by racket/stxparam, since it is normally used in a transformer. It is provided normally by racket/stxparam-exptime.

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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

11.1	Pattern-Based Syntax Matching
11.2	Syntax Object Content
11.3	Syntax Object Bindings
11.4	Syntax Transformers
11.5	Syntax Parameters
11.6	Local Binding with Splicing Body
11.7	Syntax Object Properties
11.8	Syntax Taints
11.9	Expanding Top-Level Forms
11.10	File Inclusion
11.11	Syntax Utilities