diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -4422,6 +4422,7 @@
     'PhabricatorProjectsWatchersSearchEngineAttachment' => 'applications/project/engineextension/PhabricatorProjectsWatchersSearchEngineAttachment.php',
     'PhabricatorPronounSetting' => 'applications/settings/setting/PhabricatorPronounSetting.php',
     'PhabricatorProtocolLog' => 'infrastructure/log/PhabricatorProtocolLog.php',
+    'PhabricatorPureChartFunction' => 'applications/fact/chart/PhabricatorPureChartFunction.php',
     'PhabricatorPygmentSetupCheck' => 'applications/config/check/PhabricatorPygmentSetupCheck.php',
     'PhabricatorQuery' => 'infrastructure/query/PhabricatorQuery.php',
     'PhabricatorQueryConstraint' => 'infrastructure/query/constraint/PhabricatorQueryConstraint.php',
@@ -9155,7 +9156,7 @@
     'PhabricatorConpherenceWidgetVisibleSetting' => 'PhabricatorInternalSetting',
     'PhabricatorConsoleApplication' => 'PhabricatorApplication',
     'PhabricatorConsoleContentSource' => 'PhabricatorContentSource',
-    'PhabricatorConstantChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorConstantChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorContactNumbersSettingsPanel' => 'PhabricatorSettingsPanel',
     'PhabricatorContentSource' => 'Phobject',
     'PhabricatorContentSourceModule' => 'PhabricatorConfigModule',
@@ -9167,7 +9168,7 @@
     'PhabricatorCoreCreateTransaction' => 'PhabricatorCoreTransactionType',
     'PhabricatorCoreTransactionType' => 'PhabricatorModularTransactionType',
     'PhabricatorCoreVoidTransaction' => 'PhabricatorModularTransactionType',
-    'PhabricatorCosChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorCosChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorCountFact' => 'PhabricatorFact',
     'PhabricatorCountdown' => array(
       'PhabricatorCountdownDAO',
@@ -10068,7 +10069,7 @@
       'PhabricatorMarkupInterface',
     ),
     'PhabricatorMarkupPreviewController' => 'PhabricatorController',
-    'PhabricatorMaxChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorMaxChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorMemeEngine' => 'Phobject',
     'PhabricatorMemeRemarkupRule' => 'PhutilRemarkupRule',
     'PhabricatorMentionRemarkupRule' => 'PhutilRemarkupRule',
@@ -10135,7 +10136,7 @@
     'PhabricatorMetronome' => 'Phobject',
     'PhabricatorMetronomeTestCase' => 'PhabricatorTestCase',
     'PhabricatorMetronomicTriggerClock' => 'PhabricatorTriggerClock',
-    'PhabricatorMinChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorMinChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorModularTransaction' => 'PhabricatorApplicationTransaction',
     'PhabricatorModularTransactionType' => 'Phobject',
     'PhabricatorMonogramDatasourceEngineExtension' => 'PhabricatorDatasourceEngineExtension',
@@ -10950,6 +10951,7 @@
     'PhabricatorProjectsWatchersSearchEngineAttachment' => 'PhabricatorSearchEngineAttachment',
     'PhabricatorPronounSetting' => 'PhabricatorSelectSetting',
     'PhabricatorProtocolLog' => 'Phobject',
+    'PhabricatorPureChartFunction' => 'PhabricatorChartFunction',
     'PhabricatorPygmentSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorQuery' => 'Phobject',
     'PhabricatorQueryConstraint' => 'Phobject',
@@ -11208,7 +11210,7 @@
       'PhabricatorPolicyInterface',
     ),
     'PhabricatorSavedQueryQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
-    'PhabricatorScaleChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorScaleChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorScheduleTaskTriggerAction' => 'PhabricatorTriggerAction',
     'PhabricatorScopedEnv' => 'Phobject',
     'PhabricatorSearchAbstractDocument' => 'Phobject',
@@ -11299,12 +11301,12 @@
     'PhabricatorSetupIssue' => 'Phobject',
     'PhabricatorSetupIssueUIExample' => 'PhabricatorUIExample',
     'PhabricatorSetupIssueView' => 'AphrontView',
-    'PhabricatorShiftChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorShiftChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorShortSite' => 'PhabricatorSite',
     'PhabricatorShowFiletreeSetting' => 'PhabricatorSelectSetting',
     'PhabricatorSignDocumentsUserLogType' => 'PhabricatorUserLogType',
     'PhabricatorSimpleEditType' => 'PhabricatorEditType',
-    'PhabricatorSinChartFunction' => 'PhabricatorChartFunction',
+    'PhabricatorSinChartFunction' => 'PhabricatorPureChartFunction',
     'PhabricatorSite' => 'AphrontSite',
     'PhabricatorSlackAuthProvider' => 'PhabricatorOAuth2AuthProvider',
     'PhabricatorSlowvoteApplication' => 'PhabricatorApplication',
diff --git a/src/applications/fact/chart/PhabricatorConstantChartFunction.php b/src/applications/fact/chart/PhabricatorConstantChartFunction.php
--- a/src/applications/fact/chart/PhabricatorConstantChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorConstantChartFunction.php
@@ -1,7 +1,7 @@
 <?php
 
 final class PhabricatorConstantChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'constant';
 
diff --git a/src/applications/fact/chart/PhabricatorCosChartFunction.php b/src/applications/fact/chart/PhabricatorCosChartFunction.php
--- a/src/applications/fact/chart/PhabricatorCosChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorCosChartFunction.php
@@ -1,7 +1,7 @@
 <?php
 
 final class PhabricatorCosChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'cos';
 
diff --git a/src/applications/fact/chart/PhabricatorMaxChartFunction.php b/src/applications/fact/chart/PhabricatorMaxChartFunction.php
--- a/src/applications/fact/chart/PhabricatorMaxChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorMaxChartFunction.php
@@ -1,36 +1,27 @@
 <?php
 
 final class PhabricatorMaxChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'max';
 
   protected function newArguments() {
     return array(
-      $this->newArgument()
-        ->setName('x')
-        ->setType('function'),
       $this->newArgument()
         ->setName('max')
         ->setType('number'),
     );
   }
 
-  public function getDomain() {
-    return $this->getArgument('x')->getDomain();
-  }
-
-  public function newInputValues(PhabricatorChartDataQuery $query) {
-    return $this->getArgument('x')->newInputValues($query);
-  }
-
   public function evaluateFunction(array $xv) {
-    $yv = $this->getArgument('x')->evaluateFunction($xv);
     $max = $this->getArgument('max');
 
-    foreach ($yv as $k => $y) {
-      if ($y > $max) {
-        $yv[$k] = null;
+    $yv = array();
+    foreach ($xv as $x) {
+      if ($x > $max) {
+        $yv[] = null;
+      } else {
+        $yv[] = $x;
       }
     }
 
diff --git a/src/applications/fact/chart/PhabricatorMinChartFunction.php b/src/applications/fact/chart/PhabricatorMinChartFunction.php
--- a/src/applications/fact/chart/PhabricatorMinChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorMinChartFunction.php
@@ -1,36 +1,27 @@
 <?php
 
 final class PhabricatorMinChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'min';
 
   protected function newArguments() {
     return array(
-      $this->newArgument()
-        ->setName('x')
-        ->setType('function'),
       $this->newArgument()
         ->setName('min')
         ->setType('number'),
     );
   }
 
-  public function getDomain() {
-    return $this->getArgument('x')->getDomain();
-  }
-
-  public function newInputValues(PhabricatorChartDataQuery $query) {
-    return $this->getArgument('x')->newInputValues($query);
-  }
-
   public function evaluateFunction(array $xv) {
-    $yv = $this->getArgument('x')->evaluateFunction($xv);
     $min = $this->getArgument('min');
 
-    foreach ($yv as $k => $y) {
-      if ($y < $min) {
-        $yv[$k] = null;
+    $yv = array();
+    foreach ($xv as $x) {
+      if ($x < $min) {
+        $yv[] = null;
+      } else {
+        $yv[] = $x;
       }
     }
 
diff --git a/src/applications/fact/chart/PhabricatorPureChartFunction.php b/src/applications/fact/chart/PhabricatorPureChartFunction.php
new file mode 100644
--- /dev/null
+++ b/src/applications/fact/chart/PhabricatorPureChartFunction.php
@@ -0,0 +1,4 @@
+<?php
+
+abstract class PhabricatorPureChartFunction
+  extends PhabricatorChartFunction {}
diff --git a/src/applications/fact/chart/PhabricatorScaleChartFunction.php b/src/applications/fact/chart/PhabricatorScaleChartFunction.php
--- a/src/applications/fact/chart/PhabricatorScaleChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorScaleChartFunction.php
@@ -1,7 +1,7 @@
 <?php
 
 final class PhabricatorScaleChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'scale';
 
diff --git a/src/applications/fact/chart/PhabricatorShiftChartFunction.php b/src/applications/fact/chart/PhabricatorShiftChartFunction.php
--- a/src/applications/fact/chart/PhabricatorShiftChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorShiftChartFunction.php
@@ -1,7 +1,7 @@
 <?php
 
 final class PhabricatorShiftChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'shift';
 
diff --git a/src/applications/fact/chart/PhabricatorSinChartFunction.php b/src/applications/fact/chart/PhabricatorSinChartFunction.php
--- a/src/applications/fact/chart/PhabricatorSinChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorSinChartFunction.php
@@ -1,7 +1,7 @@
 <?php
 
 final class PhabricatorSinChartFunction
-  extends PhabricatorChartFunction {
+  extends PhabricatorPureChartFunction {
 
   const FUNCTIONKEY = 'sin';
 
diff --git a/src/applications/project/chart/PhabricatorProjectBurndownChartEngine.php b/src/applications/project/chart/PhabricatorProjectBurndownChartEngine.php
--- a/src/applications/project/chart/PhabricatorProjectBurndownChartEngine.php
+++ b/src/applications/project/chart/PhabricatorProjectBurndownChartEngine.php
@@ -32,12 +32,14 @@
     if ($project_phids) {
       foreach ($project_phids as $project_phid) {
         $function = $this->newFunction(
-          'min',
           array(
             'accumulate',
             array('fact', 'tasks.open-count.assign.project', $project_phid),
           ),
-          0);
+          array(
+            'min',
+            0,
+          ));
 
         $function->getFunctionLabel()
           ->setName(pht('Tasks Moved Into Project'))
@@ -47,12 +49,14 @@
         $functions[] = $function;
 
         $function = $this->newFunction(
-          'min',
           array(
             'accumulate',
             array('fact', 'tasks.open-count.status.project', $project_phid),
           ),
-          0);
+          array(
+            'min',
+            0,
+          ));
 
         $function->getFunctionLabel()
           ->setName(pht('Tasks Reopened'))
@@ -68,20 +72,24 @@
             array('fact', 'tasks.open-count.create.project', $project_phid),
           ),
           array(
-            'max',
             array(
               'accumulate',
               array('fact', 'tasks.open-count.status.project', $project_phid),
             ),
-            0,
+            array(
+              'max',
+              0,
+            ),
           ),
           array(
-            'max',
             array(
               'accumulate',
               array('fact', 'tasks.open-count.assign.project', $project_phid),
             ),
-            0,
+            array(
+              'max',
+              0,
+            ),
           ));
 
         $function->getFunctionLabel()