Add "sum" function

Sum all arguments on stack.

Signed-off-by: Nathaniel Clark <Nathaniel.Clark@misrule.us>

src/fixtures/help.html

@@ -71,6 +71,7 @@ <h1>RPN-rs is a graphical reverse polish notation (RPN) calculator</h1>
       <tr><td>sqrt</td><td>1</td><td>Square root</td><td><i>./&macr;x</i></td></tr>
       <tr><td>trunc(ate)</td><td>1</td><td colspan=2>Truncate value to Integer</td></tr>
       <tr><td>round | rnd</td><td>1</td><td colspan=2>Round value to Integer (a half, rounds away from zero)</td></tr>
+      <tr><td>sum</td><td><i>all</i></td><td colspan=2>Add all values on stack togther and return sum</td></tr>
       <tr><th colspan=4>Scalar Operations</th></tr>
       <tr><td>factor</td><td>1</td><td colspan=2>Find all <a href="https://en.wikipedia.org/wiki/Prime_number">prime</a> factors of item</td></tr>
       <tr><td>ln</td><td>1</td><td><a href="https://en.wikipedia.org/wiki/Natural_logarithm">Natural logarithm</a></td><td><i>ln(x)</i></td></tr>

src/main.rs

@@ -174,6 +174,7 @@ fn main() {
                     "round" | "rnd" => stacks[0].try_unary(|a| a.try_round()),
                     "trunc" | "truncate" => stacks[0].try_unary(|a| a.try_trunc()),
                     "factor" => stacks[0].try_unary_v(|a| a.try_factor()),
+                    "sum" => stacks[0].try_reduce(|acc, e| acc + e),
                     // Matrix Operations
                     "det" | "determinant" => stacks[0].try_unary(|a| a.try_det()),
                     "trans" | "transpose" => stacks[0].try_unary(|a| a.try_transpose()),

src/stack.rs

@@ -19,6 +19,7 @@ pub trait StackOps {
     fn try_unary_v<F: Fn(Value) -> Result<Vec<Value>, String>>(&mut self, f: F) -> Return;
     fn unary_v<F: Fn(Value) -> Vec<Value>>(&mut self, f: F) -> Return;
     fn binary_v<F: Fn(Value, Value) -> Vec<Value>>(&mut self, f: F) -> Return;
+    fn try_reduce<F: Fn(Value, Value) -> Result<Value, String>>(&mut self, f: F) -> Return;
 }
 
 impl StackOps for Vec<Value> {
@@ -104,4 +105,19 @@ impl StackOps for Vec<Value> {
             Return::Noop
         }
     }
+    // This is roughly Iterator::try_reduce() but needs to consume self
+    fn try_reduce<F: Fn(Value, Value) -> Result<Value, String>>(&mut self, f: F) -> Return {
+        if let Some(mut acc) = self.pop() {
+            while let Some(e) = self.pop() {
+                match f(acc, e) {
+                    Ok(c) => acc = c,
+                    Err(e) => return Return::Err(e),
+                }
+            }
+            self.push(acc);
+            Return::Ok
+        } else {
+            Return::Noop
+        }
+    }
 }