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NamedParametersCowan

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== Named Parameters ==

In this design, keywords are disjoint from symbols, but there is no special syntax for them: for each keyword, a variable is bound to the value of that keyword.  Keywords must be compared with `keyword=?` rather than with `eq?`.

== Syntax ==

`(lambda/keywords `''arg'' ... `(`''key''` `''value''`) `...`) ''body'' ...`)`  [syntax]

Returns a procedure whose body is ''body'' that accepts non-keyword arguments ''args'' and keyword arguments whose names are ''keys''.  ''Values'' specify the default value for the corresponding ''keys''.

Note that ''keys'' need not have any particular syntax such as beginning with or ending with a colon, but they may do so by convention.  As identifiers, keywords must be explicitly exported from modules.

`(define/keywords (`''name''` `''arg'' ... `(`''key''` `''value''`) `...`) ''body'' ...`)`  [syntax]

Defines a procedure named ''name'' with body `(lambda/keywords `''arg'' ... `(`''key''` `''value''`) `...`) `''body'' ...`)`

== Procedures ==

`(make-keyword `''symbol''`)`

Constructs and returns a keyword object whose name is ''symbol''.

`(keyword? `''obj''`)`

Returns `#t` if ''obj'' is a keyword object, and `#f` otherwise.

`(keyword=? `''kw1''` `''kw2''`)`

Returns `#t` if ''kw1'' and ''kw2'' are keywords with the same name, and `#f` if they have different names.  It is an error if ''kw1'' and ''kw2'' are not keyword objects.

== Rationale and implementation ==

See KeywordArgumentsArcfide.  The syntax keywords `define/keywords` and `lambda/keywords` here correspond to `define/optional` and `lambda/opt` there.

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2010-09-28 04:11:02