Made range exclusive, and refactored if statement to use pattern matching

Author: alexmozaidze

src/default_environment.rs

@@ -248,14 +248,14 @@ pub fn default_env() -> Env {
                         .ok_or(RuntimeError::new("Failed converting `BigInt` to `usize`"))?
                     );
 
-                    while i <= end {
+                    while i < end {
                         res.push(i.clone());
                         i += 1;
                     }
 
                     Ok(Value::List(res.into_iter().map(Value::Int).collect::<List>()))
                 } else {
-                    Ok(Value::List((start..=end).map(Value::Int).collect::<List>()))
+                    Ok(Value::List((start..end).map(Value::Int).collect::<List>()))
                 }
             }
         }),

src/parser.rs

@@ -336,8 +336,8 @@ fn read<'a>(
                 };
                 quote_next = false;
 
-                if !stack.is_empty() {
-                    if let ParseTree::List { vec, quoted: _ } = stack.last_mut().unwrap() {
+                if let Some(last) = stack.last_mut() {
+                    if let ParseTree::List { vec, quoted: _ } = last {
                         vec.push(expr);
                     }
                     None