Chapter 42

stxparam.ss: Syntax Parameters

To load: (require (lib "stxparam.ss"))

(define-syntax-parameter identifier expr)      SYNTAX

Binds identifier 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 identifier 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 identifier can be used as a macro. If expr produces a rename-transformer result, then identifier can be used as a macro that expands to a use of the target identifier, but syntax-local-value of identifier does not produce the target's value.

(syntax-parameterize ((identifier expr) ···) body-expr ···1)      SYNTAX

Each identifier 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 identifier.

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

(syntax-parameter-value id-stx)      PROCEDURE

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.

(make-parameter-rename-transformer id-stx)      PROCEDURE

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 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 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 MzScheme's make-rename-transformer.