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Re: [xsl] The specification of the standard function fold-left


Subject: Re: [xsl] The specification of the standard function fold-left
From: "Wolfgang Laun wolfgang.laun@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sun, 22 Jun 2014 06:08:46 -0000

A couple of remarks:

On 22/06/2014, Dimitre Novatchev dnovatchev@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>  The section "16.2.3 fn:fold-left" of the W3C document "XPath and
> XQuery Functions and Operators 3.0", contains this text:
>
> "As a consequence of the function signature and the function calling
> rules, a type error occurs if the supplied function $f cannot be
> applied to two arguments, where the first argument is either the value
> of $zero or the result of a previous application of $f, and the second
> is $seq or any trailing subsequence of $seq"
>
> The signature of the function fold-left is specified as:
>
> fn:fold-left($seq as item()*,
>                  $zero as item()*,
>                  $f as function(item()*, item()) as item()*) as item()*
>
> The above quoted paragraph violates the signature, because the
> argument $f, as specified cannot have as its second argument a
> sequence -- the type of the second argument of $f must be item(). But
> the above quoted paragraph says "...the second is $seq or any trailing
> subsequence of $seq".

Since each call of $f is done with fn:head($seq), and the restriction
defined here refers to the second argument of fn:fold-left I see no
problem with this text.


>
> Exactly the same paragraph is used in the specification of fold-right
> -- and in that case the text is correct.

The paragraphs headed "Error Conditions" do differ:

...either the value of $zero or the result of a previous application
of $f, and the second is $seq or any trailing subsequence of $seq.

...any item in the sequence $seq, and the second is either the value
of $zero or the result of a previous application of $f.

-W

>
> It seems that the paragraph was copied from the fold-right
> specification into the specification of fold-left and this led to the
> observed error.
>
> Hope this would help and lead to a future correction.
>
> --
> Cheers,
> Dimitre Novatchev
> ---------------------------------------
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