Added bit shift

error.go

@@ -6,6 +6,7 @@ const (
 	ErrorUnknownOpcode Error = iota
 	ErrorDivideByZero
 	ErrorWrongOperandCount
+	ErrorNegativeShiftAmount
 )
 
 func (err Error) Error () (description string) {
@@ -15,7 +16,9 @@ func (err Error) Error () (description string) {
 	case ErrorDivideByZero:
 		description = "division by zero"
 	case ErrorWrongOperandCount:
-		description = "wrong amount of operands"
+		description = "wrong operand amount"
+	case ErrorNegativeShiftAmount:
+		description = "negative shift amount"
 	}
 	return
 }

main.go

@@ -80,7 +80,10 @@ func onPress (button stone.Button) {
 		redraw()
 		application.Draw()
 		
-	case '+', '-', '*', '/', 'p', 'r', '%', '|', '~', '&', '^', 'm':
+	case
+		'+', '-', '*', '/', 'p', 'r', '%', '|', '~', '&', '^', 'm',
+		'<', '>':
+		
 		insertOperation(rune(button))
 		redraw()
 		application.Draw()
@@ -232,6 +235,8 @@ func insertOperation (symbol rune) {
 	case '~': opcode = OpcodeNot
 	case '&': opcode = OpcodeAnd
 	case '^': opcode = OpcodeXor
+	case '<': opcode = OpcodeLeftShift
+	case '>': opcode = OpcodeRightShift
 	case 'm': opcode = OpcodeMean
 	}
 
@@ -341,6 +346,9 @@ func drawInput () {
 
 func drawNumberReadouts () {
 	_, height := application.Size()
+	
+	clear(0, height - 10, 25, 10)
+		
 	var number int64
 	var err error
 	if selectedExpression != nil {
@@ -348,7 +356,6 @@ func drawNumberReadouts () {
 	}
 
 	if err != nil {
-		clear(0, height - 10, 25, 10)
 		application.SetDot((25 - len(err.Error())) / 2, height - 6)
 		fmt.Fprint(application, err.Error())
 	} else {

tree.go

@@ -24,25 +24,29 @@ const (
 	OpcodeNot
 	OpcodeAnd
 	OpcodeXor
+	OpcodeLeftShift
+	OpcodeRightShift
 
 	OpcodeMean
 )
 
 func (opcode Opcode) String () (output string) {
 	switch opcode {
-	case OpcodeUnknown:  output = "?"
-	case OpcodeAdd:      output = "+"
-	case OpcodeSubtract: output = "-"
-	case OpcodeMultiply: output = "*"
-	case OpcodeDivide:   output = "/"
-	case OpcodePower:    output = "p"
-	case OpcodeRoot:     output = "r"
-	case OpcodeModulo:   output = "%"
-	case OpcodeOr:       output = "|"
-	case OpcodeNot:      output = "~"
-	case OpcodeAnd:      output = "&"
-	case OpcodeXor:      output = "^"
-	case OpcodeMean:     output = "mean"
+	case OpcodeUnknown:    output = "?"
+	case OpcodeAdd:        output = "+"
+	case OpcodeSubtract:   output = "-"
+	case OpcodeMultiply:   output = "*"
+	case OpcodeDivide:     output = "/"
+	case OpcodePower:      output = "p"
+	case OpcodeRoot:       output = "r"
+	case OpcodeModulo:     output = "%"
+	case OpcodeOr:         output = "|"
+	case OpcodeNot:        output = "~"
+	case OpcodeAnd:        output = "&"
+	case OpcodeXor:        output = "^"
+	case OpcodeLeftShift:  output = "<<"
+	case OpcodeRightShift: output = ">>"
+	case OpcodeMean:       output = "mean"
 	}
 	return
 }
@@ -341,6 +345,42 @@ func (operation *Operation) Solution () (solution int64, err error) {
 				solution ^= subSolution
 			}
 		}
+	case OpcodeLeftShift:
+		if len(operation.operands) != 2 {
+			err = ErrorWrongOperandCount
+			return
+		}
+
+		var left, right int64
+		left, err = operation.operands[0].Solution()
+		if err != nil { return }
+		right, err = operation.operands[1].Solution()
+		if err != nil { return }
+
+		if right < 0 {
+			err = ErrorNegativeShiftAmount
+			return
+		}
+
+		solution = left << right
+	case OpcodeRightShift:
+		if len(operation.operands) != 2 {
+			err = ErrorWrongOperandCount
+			return
+		}
+
+		var left, right int64
+		left, err = operation.operands[0].Solution()
+		if err != nil { return }
+		right, err = operation.operands[1].Solution()
+		if err != nil { return }
+
+		if right < 0 {
+			err = ErrorNegativeShiftAmount
+			return
+		}
+
+		solution = left >> right
 	case OpcodeMean:
 		if len(operation.operands) == 0 { break }
 		for _, operand := range operation.operands {