Migrate implementation of interval pointFrom from elm layer to datatype

Author: dehall

src/datatypes/interval.ts

@@ -647,6 +647,17 @@ export class Interval {
     }
   }
 
+  pointFrom() {
+    const start = this.start();
+    if (cmp.equals(start, this.end())) {
+      return start;
+    }
+
+    throw new Error(
+      'PointFrom operator may only be used on an interval containing a single point.'
+    );
+  }
+
   toString() {
     const start = this.lowClosed ? '[' : '(';
     const end = this.highClosed ? ']' : ')';

src/elm/interval.ts

@@ -5,7 +5,6 @@ import { convertUnit, compareUnits, convertToCQLDateUnit } from '../util/units';
 import * as dtivl from '../datatypes/interval';
 import { Context } from '../runtime/context';
 import { build } from './builder';
-import { equals } from '../util/comparison';
 import { ELM_NAMED_TYPE_SPECIFIER } from '../util/elmTypes';
 
 export class Interval extends Expression {
@@ -211,16 +210,7 @@ export class PointFrom extends Expression {
     if (interval == null) {
       return null;
     }
-    const start = interval.start();
-    const end = interval.end();
-
-    if (start == end || equals(start, end)) {
-      return start;
-    }
-
-    throw new Error(
-      'PointFrom operator may only be used on an interval containing a single point.'
-    );
+    return interval.pointFrom();
   }
 }