define non-instruction bytes to just get eaten (for easier text printing), and add a special case for _ -> space

README.md

@@ -1,13 +1,13 @@
 # Stupid Worm Languag
-- program space is an arbitrary sized grid
-- the worm starts where you place the worm head @
+- program space is an arbitrary sized grid of bytes
+- the worm starts as just a head `@`
 - as it passes over commands, they get moved to the back of the worm
 - values get pushed to stack (eaten) when passed over, worm body length increases
 - the program gets rearranged every time the worm executes it
 
 ## commands
 ```
-+- pop 2 values *, push sum/difference (uses the order they are popped, so `0 -` negates the top of the stack)
++- pop 2 values, push sum/difference (uses the order they are popped, so `0-` negates the top of the stack)
 ><^v change direction
 0..9 push number to stack
 /\ pop stack, reflect to the side if not zero
@@ -15,5 +15,6 @@
 = duplicate top of stack
 ! pop and write output as ascii char
 " pop and write output as number
+_ push a space character
+all other characters are pushed as-is
 ```
-* pop when stack is empty yields zero

src/main.rs

@@ -225,10 +225,8 @@ impl SandWormInterpreter {
 				}
 			}
 			b' ' | 0 => dont_push_instruction = true,
-			other => {
-				self.worm_in.push(other);
-				dont_push_instruction = true;
-			}
+			b'_' => self.worm_in.push(b' '),
+			other => self.worm_in.push(other),
 		}
 		if !dont_push_instruction {
 			self.worm_out.insert(0, instruction);