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Re: keyword procedures?

From: Alex Shinn
Subject: Re: keyword procedures?
Date: Mon, 24 Jun 2002 10:43:05 +0900
User-agent: Wanderlust/2.8.1 (Something) Emacs/21.2 Mule/5.0 (SAKAKI)

>>>>> "Thomas" == Thomas Bushnell, BSG <address@hidden> writes:

    Thomas> The guile manual suggests that Guile has support keyword
    Thomas> arguments, but contains no information beyond a chapter
    Thomas> heading.

    Thomas> But it looks like it's in ice-9/optarg.scm.  So some
    Thomas> questions:

    Thomas>   *Exactly* when are default expressions evaluated, and with
    Thomas>   what bindings already made?

Looks like lambda* expands into let-optional* => let-keywords* => let*
where each keyword is bound in the order it's defined and the defaults
are not evaluated unless the keyword is not given.  You can play with
macroexpanding the examples in the source.

    Thomas>   I need to generate keywords programmatically.  What is the
    Thomas>   analog of string->symbol for keywords, and can you give an
    Thomas>   example of its use?

Been playing with this myself recently for a home-brew object system:

guile> (apropos "keyword")
(guile): symbol->keyword        #<procedure symbol->keyword (symbol)>
(guile): keyword->symbol        #<procedure keyword->symbol (kw)>
(guile): keyword-like-symbol->keyword   #<procedure 
keyword-like-symbol->keyword (sym)>
(guile): make-keyword-from-dash-symbol  #<primitive-procedure 
(guile): keyword?       #<primitive-procedure keyword?>
(guile): keyword-dash-symbol    #<primitive-procedure keyword-dash-symbol>

    Thomas>   Is lambda* more widely implemented than just in Guile?

I've never seen it elsewhere... the keyword handling looks more
portable, as bigloo, kawa and gauche all support keywords.


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