问题
I try to write a simple function to provide me with a random letter each time i call it but I have difficulties combining my idea with the concept of a functional programing approach. Some help along the way would be appreciated! The code I have looks like:
<xd:doc>
<xd:desc>Provides one random letter, if the type is provided it returns a letter of thet type</xd:desc>
<xd:param name="type">The type of letter to return, one of (A,a,B,b)</xd:param>
</xd:doc>
<xsl:function name="gdpr:randomLetter" as="xs:string">
<xsl:param name="type" as="xs:string"></xsl:param>
<xsl:choose>
<xsl:when test="$type = 'A'">
<xsl:variable name="randomNumber" select="random-number-generator()['next']?permute(1 to 7)[1]"/>
<xsl:variable name="letters" select="('A','O','U','E','I','Y','Q')"/>
<xsl:value-of select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:when test="$type = 'a'">
<xsl:variable name="randomNumber" select="random-number-generator()['next']?permute(1 to 7)[1]"/>
<xsl:variable name="letters" select="('a','o','u','e','i','y','q')"/>
<xsl:value-of select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:when test="$type = 'B'">
<xsl:variable name="randomNumber" select="random-number-generator()['next']?permute(1 to 19)[1]"/>
<xsl:variable name="letters" select="('W','R','T','P','S','D','F','G','H','J','K','L','M','N','B','V','C','X','Z')"/>
<xsl:value-of select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:when test="$type = 'b'">
<xsl:variable name="randomNumber" select="random-number-generator()['next']?permute(1 to 19)[1]"/>
<xsl:variable name="letters" select="('w','r','t','p','s','d','f','g','h','j','k','l','m','n','b','v','c','x','z')"/>
<xsl:value-of select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:otherwise>
<xsl:variable name="randomNumber" select="random-number-generator()['next']?permute(1 to 52)[1]"/>
<xsl:variable name="letters" select="('A','O','U','E','I','Y','Q','a','o','u','e','i','y','q','w','r','t','p','s','d','f','g','h','j','k','l','m','n','b','v','c','x','z','W','R','T','P','S','D','F','G','H','J','K','L','M','N','B','V','C','X','Z')"/>
<xsl:value-of select="$letters[$randomNumber]"/>
</xsl:otherwise>
</xsl:choose>
</xsl:function>
回答1:
Your question encapsulates the problem:
I try to write a simple function to provide me with a random letter each time i call it
But a function that produces different results on different invocations (with the same arguments) is not a true ("pure") function.
One way out of this is to exploit the fact that XSLT already has "impure" functions of a kind: a function that creates a new node returns a different node each time, and you can expose this by using generate-id(). So you could write
<xsl:function name="my:random" as="xs:double">
<xsl:variable name="dummy"><a/></xsl:variable>
<xsl:sequence select="fn:random-number-generator(generate-id($dummy))?permute(1 to 10)"/>
</xsl:function>
The only problem with this is that you're right on the boundaries of what's well-defined in the spec and the optimizer might not let you get away with such tricks. It's much better, if you can, to find some way of passing a different argument to the function each time it is called: for example, a sequence number, or generate-id() applied to the input node you are currently processing.
回答2:
In the context of XSLT 3, I think one way to have a "new" random-number-generator for every node you need it is to define an accumulator:
<xsl:accumulator name="rng" as="map(xs:string, item())" initial-value="random-number-generator(current-dateTime())">
<xsl:accumulator-rule match="foo[@type]" select="$value?next()"/>
</xsl:accumulator>
So that way you could implement your function as
<xsl:function name="gdpr:randomLetter" as="item()*">
<xsl:param name="type" as="xs:string"/>
<xsl:param name="rng" as="map(xs:string, item())"/>
<xsl:choose>
<xsl:when test="$type = 'A'">
<xsl:variable name="randomNumber" select="$rng?permute(1 to 7)[1]"/>
<xsl:variable name="letters" select="('A','O','U','E','I','Y','Q')"/>
<xsl:sequence select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:when test="$type = 'a'">
<xsl:variable name="randomNumber" select="$rng?permute(1 to 7)[1]"/>
<xsl:variable name="letters" select="('a','o','u','e','i','y','q')"/>
<xsl:sequence select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:when test="$type = 'B'">
<xsl:variable name="randomNumber" select="$rng?permute(1 to 19)[1]"/>
<xsl:variable name="letters" select="('W','R','T','P','S','D','F','G','H','J','K','L','M','N','B','V','C','X','Z')"/>
<xsl:sequence select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:when test="$type = 'b'">
<xsl:variable name="randomNumber" select="$rng?permute(1 to 19)[1]"/>
<xsl:variable name="letters" select="('w','r','t','p','s','d','f','g','h','j','k','l','m','n','b','v','c','x','z')"/>
<xsl:sequence select="$letters[$randomNumber]"/>
</xsl:when>
<xsl:otherwise>
<xsl:variable name="randomNumber" select="$rng?permute(1 to 52)[1]"/>
<xsl:variable name="letters" select="('A','O','U','E','I','Y','Q','a','o','u','e','i','y','q','w','r','t','p','s','d','f','g','h','j','k','l','m','n','b','v','c','x','z','W','R','T','P','S','D','F','G','H','J','K','L','M','N','B','V','C','X','Z')"/>
<xsl:sequence select="$letters[$randomNumber]"/>
</xsl:otherwise>
</xsl:choose>
</xsl:function>
and then call it with e.g.
<xsl:template match="foo[@type]">
<xsl:copy>
<xsl:value-of select="gdpr:randomLetter(@type, accumulator-before('rng'))"/>
</xsl:copy>
</xsl:template>
and make sure you use
<xsl:mode on-no-match="shallow-copy" use-accumulators="rng"/>
回答3:
The problem is that fn:random-number-generator function is deterministic. The specs itself explain that:
Both forms of the function are ·deterministic·: calling the function twice with the same arguments, within a single ·execution scope·, produces the same results.
You need to use properly the function under the key next contained in the resulted map from calling the random-number-generator function. Like the spec said:
The entry with key "next" is a zero-arity function that can be called to return another random number generator.
回答4:
For the sake of completeness, I came up with this solution but it only works for small pieces of text due to the depth of recursion.
On a sidenote- I realized my solution was waste of time as I use exist-db that does not include random-number-generator in it's XSLT implementation.
<xsl:function name="gdpr:rngRecurseStart">
<xsl:param name="text"></xsl:param>
<xsl:variable name="chars" select="functx:chars($text)"/>
<xsl:copy-of select="gdpr:rngRecurse($chars,random-number-generator(current-dateTime()),'')"></xsl:copy-of>
</xsl:function>
<xsl:function name="gdpr:rngRecurse">
<xsl:param name="chars"></xsl:param>
<xsl:param name="rngGenerator"></xsl:param>
<xsl:param name="newText"></xsl:param>
<xsl:variable name="curentchar" select="$chars[1]"></xsl:variable>
<xsl:variable name="newRngGenerator" select="$rngGenerator?next()"/>
<xsl:choose>
<xsl:when test="count($chars) >1">
<xsl:variable name="transformedChar" select="gdpr:randomLetter2($newRngGenerator,$curentchar)"/>
<xsl:variable name="resultText" select="concat($newText, $transformedChar)"/>
<xsl:copy-of select="gdpr:rngRecurse(subsequence($chars,2),$newRngGenerator,$resultText)"></xsl:copy-of>
</xsl:when>
<xsl:when test="count($chars) =1">
<xsl:variable name="transformedChar" select="gdpr:randomLetter2($newRngGenerator,$curentchar)"/>
<xsl:variable name="resultText" select="concat($newText, $transformedChar)"/>
<xsl:copy-of select="$resultText"></xsl:copy-of>
</xsl:when>
<xsl:otherwise><xsl:copy-of select="$newText"></xsl:copy-of></xsl:otherwise>
</xsl:choose>
</xsl:function>
来源：https://stackoverflow.com/questions/55832760/using-fnrandom-number-generator-to-produce-random-numbers-more-than-once