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Re: IfExpr has a mandatory else clause

From: Torsten Grust <Torsten.Grust@uni-konstanz.de>
Date: Mon, 26 Jan 2004 10:55:05 +0100
Message-ID: <16404.58361.380499.502603@gargle.gargle.HOWL>
To: "TAN Kuan Hui" <kuanhui@xemantics.com>
Cc: "Bas de Bakker" <bas@x-hive.com>, <www-ql@w3.org>

G'day all,

  grammar issues aside for a minute, I perceive XQuery as a
_functional_ query language.  The IfExpr thus constitutes a
conditional expression rather than a control flow construct (like in
procedural programming languages).

As a conditional expression, IfExpr is required to evaluate to a
well-defined value, regardless of the outcome of the tested
condition.  This is why I find it quite natural that the `else' clause
is mandatory.  What would be the value of an IfExpr in case the
conditition evaluates to false?


On January 26 (17:49 +0800), TAN Kuan Hui wrote with possible
| Syntactically seems to parse but will this cause confusion ?
| Using () instead of {} will also re-introduce the
| ambiguity with an optional else clause although distinguishable.
| So is grammar ambiguity the reason that IfExpr has a
| mandatory else clause ? Are there other design considerations ?
| Appreciate any clarification.

  | Dr. Torsten Grust                          Torsten.Grust@uni-konstanz.de |
  |                                   http://www.inf.uni-konstanz.de/~grust/ |
  | Database Research Group, University of Konstanz (Lake Constance/Germany) |
  |             (Please avoid sending me MS Word or PowerPoint attachments.) |
Received on Monday, 26 January 2004 04:59:33 UTC

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