Integer literals now support signs

draw.go

@@ -214,6 +214,8 @@ func drawOctal (xOffset, yOffset int, number uint64) {
 	application.SetColor(xOffset, yOffset, stone.ColorBlue)
 	application.SetColor(xOffset + 1, yOffset, stone.ColorBlue)
 
+	number = drawSign(xOffset, yOffset, number)
+
 	for x := 0; x < 21; x ++ {
 		bitOffset -= 3
 		

main.go

@@ -164,7 +164,11 @@ func onPress (button stone.Button, modifiers stone.Modifiers) {
 		case *IntegerLiteral:
 			integer := selectedExpression.(*IntegerLiteral)
 			integer.value *= int64(integer.displayRadix)
-			integer.value += int64(value)
+			if integer.value < 0 {
+				integer.value -= int64(value)
+			} else {
+				integer.value += int64(value)
+			}
 		}
 		
 		redraw()

tree.go

@@ -450,6 +450,13 @@ func (literal *IntegerLiteral) Previous () (previous Expression) {
 func (literal *IntegerLiteral) Render (target stone.Buffer, offset int) (moved int) {
 	var output []rune
 	value := literal.value
+
+	negative := false
+	if value < 0 {
+		negative = true
+		value *= -1
+	}
+	
 	for value > 0 {
 		digit := rune(value % int64(literal.displayRadix))
 		value /= int64(literal.displayRadix)
@@ -479,6 +486,10 @@ func (literal *IntegerLiteral) Render (target stone.Buffer, offset int) (moved i
 		output = append([]rune("0?"), output...)
 	}
 
+	if negative {
+		output = append([]rune { '-' }, output...)
+	}
+
 	for _, character := range output {
 		target.SetRune(offset + moved, 0, character)
 		if selectedExpression == literal {