added autosum

src/lib.rs

@@ -62,6 +62,7 @@ enum Words {
     Over,
     ClearStack,
     Emit,
+    Sum,
     DefineStart,
     DefineEnd,
     Definition(Definition),
@@ -301,6 +302,16 @@ impl RPN {
         Ok(())
     }
 
+    fn sum(&mut self) -> Result {
+        let mut accumulator = self.pop()?;
+
+        while let Ok(x) = self.pop() {
+            accumulator += x;
+        }
+
+        self.push(accumulator)
+    }
+
     fn define(&mut self, name: &str, definition: Definition) {
         let name = name.to_lowercase();
         self.custom.insert(name, definition);
@@ -348,6 +359,7 @@ impl RPN {
             Words::Atan => self.atan(),
             Words::Tanh => self.tanh(),
             Words::Emit => self.emit(),
+            Words::Sum => self.sum(),
             Words::Epsilon => self.push(f64::EPSILON),
             Words::Euler => self.push(std::f64::consts::E),
             Words::Pi => self.push(std::f64::consts::PI),
@@ -411,6 +423,7 @@ impl RPN {
             "tau" => Ok(Words::Tau),
             "help" | "?" => Ok(Words::Help),
             "emit" | "." => Ok(Words::Emit),
+            "sum" => Ok(Words::Sum),
             "clear" | "c" => Ok(Words::ClearStack),
             "quit" | "q" => Ok(Words::Quit),
             unk => {
@@ -537,6 +550,8 @@ impl RPN {
 
         emit or .            print the last number pushed to the stack, removing it from the stack
 
+        sum                  sum the entire stack, pushing the result back onto the stack
+
 
             Additionally, this implements a subset of FORTH for a basic level of programability.