Added the env and evaluation for addition and subtraction functions

src/types.rs

@@ -88,6 +88,18 @@ impl From<&String> for Value {
     }
 }
 
+impl From<i64> for Value {
+    fn from(num: i64) -> Self {
+        Self::Number(num)
+    }
+}
+
+impl From<&i64> for Value {
+    fn from(num: &i64) -> Self {
+        Self::Number(*num)
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
 pub struct Symbol(pub String);