`apply-gen' partial functions now generated

This produces a short-hand partial application (well, it'd be more accurate
to call the use of `f:apply' or `f:partial' long-hand, since this is most
natural).

README.md

@@ -70,11 +70,17 @@ the output included within a distribution.
 ### Partial Applications
 Dynamic function applications using `f:apply` are partially applied if
 the number of arguments provided is less than the arity of the target
-function.
+function.  For convenience, the `apply-gen` stylesheet will also
+generate functions to perform partial application without the use of
+`f:apply` for the first call, as in the first example below:
 
 ```xml
   <!-- produces a new dynamic function of arity 5 - 3 = 2 -->
   <variable name="partial"
+            select="my:arity5( 1, 2, 3 )" />
+
+  <!-- does the same, the long way -->
+  <variable name="partial-long"
             select="f:apply( my:arity5(), 1, 2, 3 )" />
 
   <!-- consequently, currying is supported -->
@@ -84,6 +90,7 @@ function.
   <!-- equiv = true() -->
   <variable name="equiv"
             select="$result
+                    = f:apply( my:arity5( 1, 2, 3 ), 4, 5 )
                     = f:apply( my:arity5(), 1, 2, 3, 4, 5 )
                     = my:arity5( 1, 2, 3, 4, 5 )" />
 ```

src/transform/apply-gen.xsl

@@ -32,6 +32,7 @@
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:f="http://www.lovullo.com/hoxsl/apply"
+  xmlns:_f="http://www.lovullo.com/hoxsl/apply/_priv"
   xmlns:fgen="http://www.lovullo.com/hoxsl/apply/gen"
   xmlns:out="http://www.lovullo.com/hoxsl/apply/gen/_out"
   exclude-result-prefixes="#default fgen">
@@ -111,6 +112,37 @@
 </template>
 
 
+<!--
+  Do not process functions that are overloaded on arity
+
+  There are a couple reasons for this:  Firstly, overloading is
+  fundamentally incompatible with partial application, because we are unable
+  to determine when a function is fully applied.  Secondly, we would have no
+  choice but to generate functions for every arity that does @emph{not}
+  exist.  Together, that would yield a very awkward implementation whereby
+  applying N arguments may apply the target function, but N-1 and N+1 may
+  result in a partial application.  That is not acceptable.
+
+  To aid in debugging, a comment is output stating that the function was
+  explicitly ignored.
+-->
+<template mode="fgen:create"
+          match="xsl:function[
+                   @name = root(.)/xsl:*/xsl:function[
+                     not( . is current() )
+                   ]/@name
+                 ]"
+          priority="5">
+  <comment>
+    <text>No definition generated for overloaded function `</text>
+    <value-of select="@name" />
+    <text>#</text>
+    <value-of select="count( xsl:param )" />
+    <text>'</text>
+  </comment>
+</template>
+
+
 <!--
   Process function definition
 -->
@@ -147,10 +179,15 @@
 
 
 <!--
-  Generate nullary function for delayed application
+  Generate dynamic application functions for the application of @var{fnref}.
 
-  This will output a node that can be later applied to a template with
+  The most important function is the nullary, which returns a dynamic
-  mode `f:apply' to invoke the associated application template.
+  function reference that can be later used to apply the function.
+
+  Functions are also generated for partial applications: given a target
+  function @var{f} of arity @var{α}, functions of arity @math{1<x<α} are
+  generated that partially apply @var{f} with @var{x} arguments; this is
+  short-hand for invoking @code{f:apply} or @code{f:partial} directly.
 -->
 <function name="fgen:create-func">
   <param name="fnref"       as="element(xsl:function)" />
@@ -161,15 +198,42 @@
   <variable name="local-name"
             select="substring-after( $fnref/@name, ':' )" />
 
+  <variable name="arity"
+            select="count( $fnref/xsl:param )" />
+
+  <variable name="params"
+            select="$fnref/xsl:param" />
+
+  <!-- the nullary simply returns a dynamic function reference -->
   <out:function name="{$name-resolv}" as="element()">
     <namespace name="{$ns-prefix}"
                select="$ns" />
 
-    <variable name="arity"
-              select="count( $fnref/xsl:param )" />
-
     <sequence select="f:make-ref( $name-resolv, $arity )" />
   </out:function>
+
+  <!-- all others perform partial applications -->
+  <for-each select="1 to ( $arity - 1 )">
+    <variable name="partial-arity"
+              select="." />
+
+    <variable name="subparams"
+              select="subsequence( $params, 1, $partial-arity )" />
+
+    <out:function name="{$name-resolv}" as="item()+">
+      <namespace name="{$ns-prefix}"
+                 select="$ns" />
+
+      <variable name="argstr"
+                select="_f:argstr-gen( $subparams )" />
+
+      <sequence select="_f:param-gen( $subparams )" />
+
+      <out:sequence select="f:partial(
+                              {$name-resolv}(),
+                              ({$argstr}) )" />
+    </out:function>
+  </for-each>
 </function>
 
 
@@ -187,7 +251,7 @@
   <param name="ns-prefix"   as="xs:string" />
   <param name="ns"          as="xs:anyURI" />
 
-  <variable name="params"
+  <variable name="params" as="element()+"
             select="$defn/xsl:param" />
 
   <out:template mode="f:apply"
@@ -196,27 +260,58 @@
     <namespace name="{$ns-prefix}"
                select="$ns" />
 
-    <for-each select="$params">
+    <sequence select="_f:param-gen( $params )" />
-      <xsl:variable name="i"
-                    select="position()" />
 
-      <out:param name="arg{$i}">
+    <variable name="argstr"
-        <copy-of select="@as" />
+              select="_f:argstr-gen( $params )" />
-      </out:param>
-    </for-each>
-
-    <variable name="argstr">
-      <for-each select="$params">
-        <if test="position() gt 1">
-          <text>, </text>
-        </if>
-        <text>$arg</text>
-        <value-of select="position()" />
-      </for-each>
-    </variable>
 
     <out:sequence select="{$name-resolv}({$argstr})" />
   </out:template>
 </function>
 
+
+<!--
+  Given a sequence of XSLT function parameters @var{params}, generate
+  enumerated argument @code{<param>}s.
+
+  This is to be used in conjunction with @code{_f:argstr-gen}.
+-->
+<function name="_f:param-gen" as="element()+">
+  <param name="params" as="element()+" />
+
+  <for-each select="$params">
+    <xsl:variable name="i"
+                  select="position()" />
+
+    <out:param name="arg{$i}">
+      <copy-of select="@as" />
+    </out:param>
+  </for-each>
+</function>
+
+
+<!--
+  Given a sequence of XSLT function parameters @var{params}, generate
+  a string that, when used in an XPath, represents a list of arguments of a
+  function application.
+
+  This is to be used in conjunction with @code{_f:param-gen}.
+-->
+<function name="_f:argstr-gen" as="xs:string">
+  <param name="params" as="element()+" />
+
+  <xsl:variable name="argstr">
+    <for-each select="$params">
+      <if test="position() gt 1">
+        <text>, </text>
+      </if>
+      <text>$arg</text>
+      <value-of select="position()" />
+    </for-each>
+  </xsl:variable>
+
+  <!-- force to string -->
+  <value-of select="string( $argstr )" />
+</function>
+
 </stylesheet>

test/transform/apply-gen-test-in.xsl

@@ -41,4 +41,30 @@
 
     <sequence select="$x - $y" />
   </function>
+
+
+  <!-- overloaded function, for which we cannot generate anything -->
+  <function name="foo:overloaded">
+    <param name="a" />
+  </function>
+  <function name="foo:overloaded">
+    <param name="a" />
+    <param name="b" />
+  </function>
+
+
+  <!-- large number of arguments to test partial application -->
+  <function name="foo:eight" as="item()+">
+    <param name="arg1" />
+    <param name="arg2" />
+    <param name="arg3" />
+    <param name="arg4" />
+    <param name="arg5" />
+    <param name="arg6" />
+    <param name="arg7" />
+    <param name="arg8" />
+
+    <sequence select="$arg1, $arg2, $arg3, $arg4,
+                      $arg5, $arg6, $arg7, $arg8" />
+  </function>
 </stylesheet>

test/transform/apply-gen.xspec

@@ -26,6 +26,20 @@
              xmlns:foo="http://www.lovullo.com/_junk"
              stylesheet="apply-gen-test.xsl">
 
+  <variable name="args">
+    <foo:args>
+      <foo:arg1 />
+      <foo:arg2 />
+      <foo:arg3 />
+      <foo:arg4 />
+      <foo:arg5 />
+      <foo:arg6 />
+      <foo:arg7 />
+      <foo:arg8 />
+    </foo:args>
+  </variable>
+
+
   <!-- basic case -->
   <scenario label="given a unary function">
     <context>
@@ -116,6 +130,27 @@
   </scenario>
 
 
+  <!-- see SUT for rationale -->
+  <scenario label="given an arity-overloaded function">
+    <context>
+      <xsl:stylesheet>
+        <xsl:function name="foo:overloaded">
+          <xsl:param name="a" />
+        </xsl:function>
+
+        <xsl:function name="foo:overloaded">
+          <xsl:param name="a" />
+          <xsl:param name="b" />
+        </xsl:function>
+      </xsl:stylesheet>
+    </context>
+
+    <expect label="yields no functions of that name"
+            test="not( xsl:stylesheet/xsl:function[
+                         @name='foo:overloaded' ] )" />
+  </scenario>
+
+
   <scenario label="given a stylesheet">
     <scenario label="with no function elements">
       <context>
@@ -218,5 +253,203 @@
                 select="2" />
       </scenario>
     </scenario>
+
+
+    <!-- more duplication...we support up to eight arguments, so we'll
+         have to test the generation of 1..7 (nullary is already
+         tested and 8 results in a full application) -->
+    <scenario label="with partial functions of 8-ary target, given">
+      <variable name="qname"
+                select="QName( 'http://www.lovullo.com/_junk',
+                               'foo:eight' )" />
+
+      <scenario label="one argument">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 7" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1" />
+      </scenario>
+
+
+      <scenario label="two arguments">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+          <param name="arg2" select="$args/foo:arg2" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 6" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1
+                      and $result-args[ 2 ] is $args/foo:arg2" />
+      </scenario>
+
+
+      <scenario label="three arguments">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+          <param name="arg2" select="$args/foo:arg2" />
+          <param name="arg3" select="$args/foo:arg3" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 5" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1
+                      and $result-args[ 2 ] is $args/foo:arg2
+                      and $result-args[ 3 ] is $args/foo:arg3" />
+      </scenario>
+
+
+      <scenario label="four arguments">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+          <param name="arg2" select="$args/foo:arg2" />
+          <param name="arg3" select="$args/foo:arg3" />
+          <param name="arg4" select="$args/foo:arg4" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 4" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1
+                      and $result-args[ 2 ] is $args/foo:arg2
+                      and $result-args[ 3 ] is $args/foo:arg3
+                      and $result-args[ 4 ] is $args/foo:arg4" />
+      </scenario>
+
+
+      <scenario label="five arguments">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+          <param name="arg2" select="$args/foo:arg2" />
+          <param name="arg3" select="$args/foo:arg3" />
+          <param name="arg4" select="$args/foo:arg4" />
+          <param name="arg5" select="$args/foo:arg5" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 3" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1
+                      and $result-args[ 2 ] is $args/foo:arg2
+                      and $result-args[ 3 ] is $args/foo:arg3
+                      and $result-args[ 4 ] is $args/foo:arg4
+                      and $result-args[ 5 ] is $args/foo:arg5" />
+      </scenario>
+
+
+      <scenario label="six arguments">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+          <param name="arg2" select="$args/foo:arg2" />
+          <param name="arg3" select="$args/foo:arg3" />
+          <param name="arg4" select="$args/foo:arg4" />
+          <param name="arg5" select="$args/foo:arg5" />
+          <param name="arg6" select="$args/foo:arg6" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 2" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1
+                      and $result-args[ 2 ] is $args/foo:arg2
+                      and $result-args[ 3 ] is $args/foo:arg3
+                      and $result-args[ 4 ] is $args/foo:arg4
+                      and $result-args[ 5 ] is $args/foo:arg5
+                      and $result-args[ 6 ] is $args/foo:arg6" />
+      </scenario>
+
+
+      <scenario label="seven arguments">
+        <call function="foo:eight">
+          <param name="arg1" select="$args/foo:arg1" />
+          <param name="arg2" select="$args/foo:arg2" />
+          <param name="arg3" select="$args/foo:arg3" />
+          <param name="arg4" select="$args/foo:arg4" />
+          <param name="arg5" select="$args/foo:arg5" />
+          <param name="arg6" select="$args/foo:arg6" />
+          <param name="arg7" select="$args/foo:arg7" />
+        </call>
+
+        <expect label="returns partially applied function"
+                test="f:is-partial( $x:result )" />
+
+        <expect label="references the target function"
+                test="f:QName( $x:result ) = $qname" />
+
+        <expect label="partially applies one argument"
+                test="f:arity( $x:result ) = 1" />
+
+        <variable name="result-args" as="item()+"
+                  select="f:args( $x:result )" />
+        <expect label="argument is partially applied by reference"
+                test="$result-args[ 1 ] is $args/foo:arg1
+                      and $result-args[ 2 ] is $args/foo:arg2
+                      and $result-args[ 3 ] is $args/foo:arg3
+                      and $result-args[ 4 ] is $args/foo:arg4
+                      and $result-args[ 5 ] is $args/foo:arg5
+                      and $result-args[ 6 ] is $args/foo:arg6
+                      and $result-args[ 7 ] is $args/foo:arg7" />
+      </scenario>
+    </scenario>
   </scenario>
 </description>