1.8.2 Defining makers

The following bindings are exported by the (vicare language-extensions makers) library.

Macro: define-maker name-spec maker-sexp keywords-defaults-options

Auxiliary Syntax: mandatory

Auxiliary Syntax: optional

Auxiliary Syntax: with identifier ...

Auxiliary Syntax: without identifier ...

Define a new maker macro. name-spec has one of the forms:

name-identifier
(name-identifier positional-arg ...)

where name-identifier is the name of the defined macro and each positional-arg is an identifier, name of a mandatory positional argument for the macro.

maker-sexp has one of the forms:

maker-expr0
(maker-expr0 maker-expr ...)

where each maker-expr is a macro keyword or an expression evaluated in the lexical context of the define-maker macro use; the expressions are evaluated every time the maker is used.

keywords-defaults-options defines optional arguments selected with an auxiliary syntax and a value; it has the form:

(clause-spec ...)

where each clause-spec has the form:

(auxiliary-syntax default-expr)
(auxiliary-syntax default-expr option ...)

where each auxiliary-syntax is an identifier and default-expr is an expression representing the default value for the argument; the expressions are all evaluated in the lexical context of the define-maker macro use, the expressions are evaluated every time the maker is used.

Notice that the auxiliary-syntax identifiers are matched against the values in the macro use by comparing the syntax objects with free-identifier=?.

Each of the option forms can be one among:

(mandatory)
(optional)
(with identifier ...)
(without identifier ...)

where the first two specify if the current clause is mandatory or optional; the with option selects a list of clauses that must be present when the current clause is used; the without option selects a list of clauses that must not be present when the current clause is used. Each clause can be used at most once; mandatory cannot appear along with optional.

When the new macro is used without optional auxiliary syntaxes, it is expanded to:

;; single maker expression, no positional arguments
(maker-expr-result)

;; single maker expression, positional arguments
(maker-expr-result
 positional-arg0 positional-arg ...)

;; multiple maker expressions, no positional arguments
(maker-expr-result0 maker-expr-result ...)

;; multiple maker expressions, positional arguments
(maker-expr-result0 maker-expr-result ...
 positional-arg0 positional-arg ...)

When the new macro is defined with optional auxiliary syntaxes, the expressions in the given syntax clauses, or the default expressions, are appended to the output form in the same order as the corresponding syntaxes in keywords-defaults-options.

It is an error if the generated maker is invoked with a clause used multiple times.

When the clause of a generated maker is used with multiple values: the values are enclosed in a list form and the result is used as argument for the maker expression; for example:

(import (vicare)
  (prefix (vicare language-extensions makers) mk.))

(define-syntax alpha:)

(mk.define-maker doit
    vector
  ((alpha: (list 1 2 3))))

(doit)                   → (vector (list 1 2 3))
(doit (alpha: 10 20 30)) → (vector (list 10 20 30))