Added "encompass" key

main.go

@@ -83,12 +83,17 @@ func onPress (button stone.Button, modifiers stone.Modifiers) {
 		}, modifiers.Alt, false, false)
 		redraw()
 		application.Draw()
+
+	case '\\':
+		insertOperation('?', false, true)
+		redraw()
+		application.Draw()
 		
 	case
 		'+', '-', '*', '/', 'p', 'P', '%', '|', '~', '&', '^', 'm',
 		'l', 'r':
 		
-		insertOperation(rune(button), modifiers.Alt)
+		insertOperation(rune(button), modifiers.Alt, false)
 		redraw()
 		application.Draw()
 
@@ -244,9 +249,10 @@ func onPress (button stone.Button, modifiers stone.Modifiers) {
 	}
 }
 
-func insertOperation (symbol rune, swap bool) {
+func insertOperation (symbol rune, swap, encompass bool) {
 	var opcode Opcode
 	switch (symbol) {
+	case '?': opcode = OpcodeUnknown
 	case '+': opcode = OpcodeAdd
 	case '-': opcode = OpcodeSubtract
 	case '*': opcode = OpcodeMultiply
@@ -263,6 +269,23 @@ func insertOperation (symbol rune, swap bool) {
 	case 'm': opcode = OpcodeMean
 	}
 
+	newExpression := Operation { opcode: opcode, floating: showFloat }
+
+	if encompass {
+		if selectedExpression == nil { return }
+		parent := selectedExpression.Parent()
+
+		newExpression.Adopt(selectedExpression)
+		if parent == nil {
+			expressionRoot = &newExpression
+		} else {
+			parent.Swap(selectedExpression, &newExpression)
+		}
+
+		selectedExpression = &newExpression
+		return
+	}
+
 	operation, isOperation := selectedExpression.(*Operation)
 	if isOperation {
 		if operation.opcode == OpcodeUnknown || swap {
@@ -270,9 +293,8 @@ func insertOperation (symbol rune, swap bool) {
 			return
 		}
 	}
-
-	newExpression := &Operation { opcode: opcode, floating: showFloat }
-	insertGeneric(newExpression, swap, false, true)
+	
+	insertGeneric(&newExpression, swap, false, true)
 }
 
 func insertNumber (value int64, swap, before bool) {