comment parsing, marbles pass through spaces in comments. fix crash on division by zero

programs/adder.mbl

@@ -0,0 +1,28 @@
+(print sum of 123 and 45)
+
+  o
+  > 123   B
+ vo      A-+
+  > 45    B|
+  o      --+
+  >      *  B
+         o
+   (check if 0)
+     o   1
+v  < B=- 0
+ v   o * D- (div/10)
+v       B *  <
+
+v> * 1    o  ^
+ F -R0  * 4 B
+*| # <  -A8 v
+ |      # <
+#|
+ -|            v   <
+  |         *-|o
+  F           +B * ^
+ #<         \F----
+(ascii digit s)
+(printed in)*-|
+(reverse)    P-
+            B

src/main.rs

@@ -22,6 +22,7 @@ enum Tile {
 	#[default]
 	Blank,
 	Block,
+	Comment(u8),
 	Bag {
 		count: u8,
 	},
@@ -179,12 +180,17 @@ impl Machine {
 				let tile = self.grid.get((x, y).into());
 				if let Tile::Marble { value, dir } = tile {
 					marbles_on_row.push((value, dir));
-					print!("{}", 'o'.green());
+					print!("{}", 'o'.magenta());
+					continue;
+				}
+				if let Tile::Comment(c) = tile {
+					print!("{}", (c as char).yellow());
 					continue;
 				}
 				let mut powered = false;
 				let c = match tile {
 					Tile::Marble { value: _, dir: _ } => unreachable!(),
+					Tile::Comment(_) => unreachable!(),
 					Tile::Blank => ' ',
 					Tile::Block => '#',
 					Tile::Bag { count: _ } => 'B',
@@ -223,12 +229,12 @@ impl Machine {
 				if powered {
 					print!("{}", c.red());
 				} else {
-					print!("{c}");
+					print!("{}", c.cyan());
 				}
 			}
 			print!(" :: ");
 			for (val, dir) in marbles_on_row {
-				print!("{}", format!("{}{:<3} ", dir.char(), val).green())
+				print!("{}", format!("{}{:<3} ", dir.char(), val).magenta())
 			}
 			println!();
 		}
@@ -337,13 +343,7 @@ impl Machine {
 							new_tile = Some(Tile::Blank);
 						}
 					}
-					Tile::Block => (),
-					_ => {
-						new_tile = Some(Tile::Marble {
-							value,
-							dir: dir.opposite(),
-						});
-					}
+					_ => (),
 				}
 
 				if let Some(t) = new_tile {
@@ -416,8 +416,8 @@ impl Machine {
 						MathOp::Add => val_a.wrapping_add(val_b),
 						MathOp::Sub => val_a.wrapping_sub(val_b),
 						MathOp::Mul => val_a.wrapping_mul(val_b),
-						MathOp::Div => val_a / val_b,
-						MathOp::Rem => val_a % val_b,
+						MathOp::Div => val_a.checked_div(val_b).unwrap_or_default(),
+						MathOp::Rem => val_a.checked_rem(val_b).unwrap_or_default(),
 					};
 					println!("{op:?} a:{val_a} b:{val_b}");
 					*self.grid.get_mut(front_pos) = Tile::Marble { value: result, dir };
@@ -468,6 +468,7 @@ impl Machine {
 			| Tile::Digit(_)
 			| Tile::Mirror(_)
 			| Tile::Arrow(_)
+			| Tile::Comment(_)
 			| Tile::Block
 			| Tile::Blank => (),
 		}
@@ -575,7 +576,20 @@ fn parse(source: &str) -> (Vec<Vec<Tile>>, Vec<Pos>) {
 	for (y, line) in source.lines().enumerate() {
 		width = width.max(line.len());
 		let mut tiles = Vec::new();
+		let mut in_comment = false;
 		for (x, char) in line.chars().enumerate() {
+			if in_comment {
+				if char == ')' {
+					in_comment = false;
+				}
+				if char == ' ' {
+					// allow marbles to pass through gaps in comments
+					tiles.push(Tile::Blank);
+				} else {
+					tiles.push(Tile::Comment(char as u8));
+				}
+				continue;
+			}
 			tiles.push(match char {
 				'o' => {
 					marbles.push((x, y).into());
@@ -609,6 +623,11 @@ fn parse(source: &str) -> (Vec<Vec<Tile>>, Vec<Pos>) {
 				'B' => Tile::Bag { count: 0 },
 				d @ '0'..='9' => Tile::Digit(d as u8),
 				'#' => Tile::Block,
+				' ' => Tile::Blank,
+				'(' => {
+					in_comment = true;
+					Tile::Comment(b'(')
+				}
 				_ => Tile::Blank,
 			});
 		}