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ISSUE-92: n-ary builtins

From: Chris Welty <cawelty@gmail.com>
Date: Fri, 27 Feb 2009 15:32:42 -0500
Message-ID: <49A84DEA.1050703@gmail.com>
To: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>

The basic issue is that BLD (and core) require all predicates and functions to 
have a fixed arity, but in DTB we reuse many xpath/xquery functions and 
predicates, and there are several that do not have a fixed arity (e.g. concat). 
      In DTB, the treatment of these operators is unclear:

"numbering the different versions of the respective built-ins and treating the 
unnumbered version as syntactic sugar, i.e. for instance instead of External( 
func:concat2( str1, str2) ) and External( func:concat3( str1 str2 str3 ) ) we 
allow the equivalent forms External( func:concat( str1, str2) ) and External( 
func:concat( str1 str2 str3 ) )."

Does this mean that BLD should allow rulesets to use concat with any arity, or 
does it mean that for the purposes of DTB we write concat as a shortcut for 
whichever (concat2, concat3, etc) is appropriate?

Possible solutions:

1) Make it clear this is only for the purposes of writing DTB, and that all 
rulesets must use a fixed arity function/predicate

2) Allow for some preprocessing step in RIF implementations where functions like 
concat are replaced with their fixed-arity equivalents

3) Change BLD to allow for arbitrary arity functions and predicates. I can find 
no formal resolution to make preds/funs fixed arity, however it would be a major 
change to a LC document (BLD).  At the last telecon, no one was opposed to this 
change on technical grounds, only because of the LC status.

I prefer option 1.

Dr. Christopher A. Welty                    IBM Watson Research Center
+1.914.784.7055                             19 Skyline Dr.
cawelty@gmail.com                           Hawthorne, NY 10532
Received on Friday, 27 February 2009 20:33:22 UTC

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