Add Display trait for Vector

@@ -130,22 +130,22 @@ fn _vector() {
     let v2 = Vector(2.into(), 2.into(), 3.into());
     let s :Fractional = 3.into();
 
-    println!("{:>14} : {:?}", "Vector v1", v1);
-    println!("{:>14} : {:?}", "Vector v2", v2);
-    println!("{:>14} : {}"  , "abs v1", v1.abs());
-    println!("{:>14} : {:?}", "-v1", -v1);
-    println!("{:>14} : {:?}", "v1 + v1", v1 + v1);
-    println!("{:>14} : {:?}", "v1 - v1", v1 - v1);
-    println!("{:>14} : {:?}", "v2 - v1", v2 - v1);
-    println!("{:>14} : {:?}", format!("v1 * {}", s), v1.mul(&s));
-    println!("{:>14} : {:?}", "norm v1", v1.norm());
-    println!("{:>14} : {}"  , "abs norm v1", v1.norm().abs());
-    println!("{:>14} : {}"  , "distance v1 v2", v1.distance(v2));
-    println!("{:>14} : {}"  , "distance v2 v1", v2.distance(v1));
-    println!("{:>14} : {}"  , "v1 dot v2", v1.dot(v2));
-    println!("{:>14} : {}"  , "v2 dot v1", v2.dot(v1));
-    println!("{:>14} : {:?}", "v1 * v2", v1 * v2);
-    println!("{:>14} : {:?}", "v2 * v1", v2 * v1);
+    println!("{:>14} : {}", "Vector v1", v1);
+    println!("{:>14} : {}", "Vector v2", v2);
+    println!("{:>14} : {}", "abs v1", v1.abs());
+    println!("{:>14} : {}", "-v1", -v1);
+    println!("{:>14} : {}", "v1 + v1", v1 + v1);
+    println!("{:>14} : {}", "v1 - v1", v1 - v1);
+    println!("{:>14} : {}", "v2 - v1", v2 - v1);
+    println!("{:>14} : {}", format!("v1 * {}", s), v1.mul(&s));
+    println!("{:>14} : {}", "norm v1", v1.norm());
+    println!("{:>14} : {}", "abs norm v1", v1.norm().abs());
+    println!("{:>14} : {}", "distance v1 v2", v1.distance(v2));
+    println!("{:>14} : {}", "distance v2 v1", v2.distance(v1));
+    println!("{:>14} : {}", "v1 dot v2", v1.dot(v2));
+    println!("{:>14} : {}", "v2 dot v1", v2.dot(v1));
+    println!("{:>14} : {}", "v1 * v2", v1 * v2);
+    println!("{:>14} : {}", "v2 * v1", v2 * v1);
 }
 
 fn main() {

@@ -19,6 +19,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //
 use std::ops::{Add, Sub, Neg, Mul};
+use std::fmt;
 use crate::{Fractional};
 
 #[derive(Debug, Eq, Clone, Copy)]
@@ -58,6 +59,12 @@ impl Vector {
     }
 }
 
+impl fmt::Display for Vector {
+    fn fmt(&self, f :&mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "({}, {}, {})", self.0, self.1, self.2)
+    }
+}
+
 impl PartialEq for Vector {
     fn eq(&self, other :&Self) -> bool {
         let Vector(x1, y1, z1) = self;