Add isNegative() to the Type\NumberInterface

src/Type/Decimal.php

@@ -37,6 +37,11 @@ final class Decimal implements NumberInterface
      */
     private $value;
 
+    /**
+     * @var bool
+     */
+    private $isNegative = false;
+
     /**
      * @param mixed $value The decimal value to store
      */
@@ -61,9 +66,18 @@ final class Decimal implements NumberInterface
             $value = '0';
         }
 
+        if (strpos($value, '-') === 0) {
+            $this->isNegative = true;
+        }
+
         $this->value = $value;
     }
 
+    public function isNegative(): bool
+    {
+        return $this->isNegative;
+    }
+
     public function toString(): string
     {
         return $this->value;