added swap stack command, bump version (#2)

calc.go

@@ -51,6 +51,8 @@ debug                toggle debug output
 dump                 display the stack contents
 clear                clear the whole stack
 shift                remove the last element of the stack
+reverse              reverse the stack elements
+swap                 exchange the last two elements
 history              display calculation history
 help|?               show this message
 quit|exit|c-d|c-c    exit program
@@ -79,7 +81,7 @@ median               median of all values`
 // commands, constants and operators,  defined here to feed completion
 // and our mode switch in Eval() dynamically
 const (
-	Commands  string = `dump reverse debug undebug clear batch shift undo help history manual exit quit`
+	Commands  string = `dump reverse debug undebug clear batch shift undo help history manual exit quit swap`
 	Constants string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
 )
 
@@ -191,20 +193,6 @@ func (c *Calc) Eval(line string) {
 			c.stack.Backup()
 			c.stack.Push(num)
 		} else {
-			/*
-				if contains(c.MathFunctions, item) {
-					// go builtin math function, if implemented
-					c.mathfunc(item)
-					continue
-				}
-
-				if contains(c.BatchFunctions, item) {
-					// math functions only supported in batch mode like max or mean
-					c.batchfunc(item)
-					continue
-				}
-			*/
-
 			if contains(c.Constants, item) {
 				// put the constant onto the stack
 				c.stack.Backup()
@@ -270,6 +258,13 @@ func (c *Calc) Eval(line string) {
 			case "reverse":
 				c.stack.Backup()
 				c.stack.Reverse()
+			case "swap":
+				if c.stack.Len() < 2 {
+					fmt.Println("stack too small, can't swap")
+				} else {
+					c.stack.Backup()
+					c.stack.Swap()
+				}
 			case "undo":
 				c.stack.Restore()
 			case "history":

main.go

@@ -30,7 +30,7 @@ import (
 	lua "github.com/yuin/gopher-lua"
 )
 
-const VERSION string = "2.0.1"
+const VERSION string = "2.0.2"
 
 const Usage string = `This is rpn, a reverse polish notation calculator cli.
 

rpn.pod

@@ -116,7 +116,9 @@ You can use B<dump> to display the stack. If debugging
 is enabled (C<-d> switch or B<debug> toggle command), then the backup
 stack is also being displayed.
 
-The stack can be reversed using the B<reverse> command.
+The  stack can  be  reversed using  the  B<reverse> command.  However,
+sometimes only  the last two  values are in  the wrong order.  Use the
+B<swap> command to exchange them.
 
 You can use the B<shift> command to remove the last number from the
 stack.

stack.go

@@ -115,6 +115,26 @@ func (s *Stack) Shift(num ...int) {
 	}
 }
 
+func (s *Stack) Swap() {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	if s.linklist.Len() < 2 {
+		return
+	}
+
+	a := s.linklist.Back()
+	s.linklist.Remove(a)
+
+	b := s.linklist.Back()
+	s.linklist.Remove(b)
+
+	s.Debug(fmt.Sprintf("swapping %.2f with %.2f", b.Value, a.Value))
+
+	s.linklist.PushBack(a.Value)
+	s.linklist.PushBack(b.Value)
+}
+
 // Return the last num items from the stack w/o modifying it.
 func (s *Stack) Last(num ...int) []float64 {
 	items := []float64{}