core: vector/minmax/_minreduce_: New template

* test/core/suite.xml: Import `test/core/vector/minmax'.
* test/core/vector/minmax.xml: New package.
* vector/minmax.xml (_minreduce_, _minreduce): New template, function.

3 files changed, 168 insertions, 3 deletions

diff --git a/core/test/core/suite.xml b/core/test/core/suite.xml
index 1375934..146ef2e 100644
--- a/core/test/core/suite.xml
+++ b/core/test/core/suite.xml
@@ -33,6 +33,7 @@
   <import package="vector/fold" />
   <import package="vector/interpolate" />
   <import package="vector/length" />
+  <import package="vector/minmax" />
   <import package="vector/table" />
 
   <import package="aggregate" />
diff --git a/core/test/core/vector/minmax.xml b/core/test/core/vector/minmax.xml
new file mode 100644
index 0000000..eadcec7
--- /dev/null
+++ b/core/test/core/vector/minmax.xml
@@ -0,0 +1,72 @@
+<?xml version="1.0"?>
+<!--
+  Copyright (C) 2014-2019 Ryan Specialty Group, LLC.
+
+  This file is part of tame-core.
+
+  tame-core is free software: you can redistribute it and/or modify it
+  under the terms of the GNU General Public License as
+  published by the Free Software Foundation, either version 3 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+-->
+<package xmlns="http://www.lovullo.com/rater"
+         xmlns:c="http://www.lovullo.com/calc"
+         xmlns:t="http://www.lovullo.com/rater/apply-template"
+         desc="Testing minimum and maximum values of vectors">
+
+  <import package="../../spec" />
+
+  <import package="../../../base" />
+  <import package="../../../vector/minmax" />
+
+
+  <t:describe name="_minreduce_">
+    <t:it desc="reduces empty vector to 0">
+      <t:given>
+        <t:minreduce>
+        </t:minreduce>
+      </t:given>
+
+      <t:expect>
+        <t:match-result eq="0" />
+      </t:expect>
+    </t:it>
+
+
+    <t:it desc="reduces one-element vector to its only element">
+      <t:given>
+        <t:minreduce>
+          <c:value-of name="#3" />
+        </t:minreduce>
+      </t:given>
+
+      <t:expect>
+        <t:match-result eq="3" />
+      </t:expect>
+    </t:it>
+
+
+    <t:it desc="reduces n-element vector to its minimum">
+      <t:given>
+        <t:minreduce>
+          <c:value-of name="#7" />
+          <c:value-of name="#3" />
+          <c:value-of name="#1" />
+          <c:value-of name="#6" />
+        </t:minreduce>
+      </t:given>
+
+      <t:expect>
+        <t:match-result eq="1" />
+      </t:expect>
+    </t:it>
+  </t:describe>
+</package>
diff --git a/core/vector/minmax.xml b/core/vector/minmax.xml
index 0a28d4f..9176384 100644
--- a/core/vector/minmax.xml
+++ b/core/vector/minmax.xml
@@ -24,14 +24,104 @@
   title="Maximum and Minimum Elements">
 
   <import package="../base" />
+  <import package="../when" />
   <import package="../numeric/common" />
   <import package="../numeric/minmax" />
 
 
   <section title="Vector Reduction">
-    Core currently only offers a~maximum reduction on
-    a~vector.  \todo{Add a~minimum reduction.}  \ref{_maxreduce_}
-    provides a convenient template-based abstraction.
+    Two types of reductions are provided for minimum and maximum respectively:
+      \ref{_minreduce_} and \ref{_maxreduce_}.\footnote{
+        This is because TAME does not have first-class functions.}
+    They both produce scalar values of the minimums and maximums
+      (respectively) of vectors.
+
+    <template name="_minreduce_"
+              desc="Reduce a vector to its minimum">
+      <param name="@values@"   desc="Values to reduce" />
+      <param name="@isvector@" desc="Set to 'true' if the nodes should
+                                     not be wrapped in c:vector" />
+
+      <param name="@label@" desc="Application label">
+        <!-- default empty -->
+        <text></text>
+      </param>
+
+
+      <c:apply name="_minreduce" label="@label@">
+        <c:arg name="vector">
+          <if name="@isvector@" eq="true">
+            <param-copy name="@values@" />
+          </if>
+          <unless name="@isvector@" eq="true">
+            <c:vector>
+              <param-copy name="@values@" />
+            </c:vector>
+          </unless>
+        </c:arg>
+      </c:apply>
+    </template>
+
+
+    <function name="_minreduce"
+              desc="Minimum value in a vector">
+      <param name="vector" type="float" set="vector"
+             desc="Vector to find minimum of" />
+
+      <c:let>
+        <c:values>
+          <c:value name="length" type="integer"
+                   desc="Length of vector">
+            <c:length-of>
+              <c:value-of name="vector" />
+            </c:length-of>
+          </c:value>
+        </c:values>
+
+        <c:cases>
+          <c:case label="Empty vector">
+            <t:when-eq name="length" value="#0" />
+
+            <c:value-of name="#0" />
+          </c:case>
+
+
+          <c:case label="Single-element vector">
+            <t:when-eq name="length" value="#1" />
+
+            <c:value-of name="vector">
+              <c:index>
+                <c:value-of name="#0" />
+              </c:index>
+            </c:value-of>
+          </c:case>
+
+
+          <c:otherwise label="Non-empty vector">
+            <c:apply name="min">
+              <c:arg name="min1">
+                <c:value-of name="vector">
+                  <c:index>
+                    <c:value-of name="#0" />
+                  </c:index>
+                </c:value-of>
+              </c:arg>
+
+              <c:arg name="min2">
+                <c:recurse>
+                  <c:arg name="vector">
+                    <c:cdr>
+                      <c:value-of name="vector" />
+                    </c:cdr>
+                  </c:arg>
+                </c:recurse>
+              </c:arg>
+            </c:apply>
+          </c:otherwise>
+        </c:cases>
+      </c:let>
+    </function>
+
 
     <template name="_maxreduce_"
               desc="Reduce a set to its maximum">
@@ -72,6 +162,8 @@
     let~expressions and other convenience templates.  It has since
     been refactored slightly, but can be made to be more concise.}
 
+    <!-- TODO: rewrite this to be more concise, with the more lisp-like
+         recursive strategy of minreduce -->
     <function name="maxreduce" desc="Reduce a set to its maximum">
       <param name="maxreduce_set" type="float" set="vector"
              desc="Set to find max of" />