save eval feature

Cargo.toml

@@ -6,3 +6,6 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+
+[features]
+save-eval = []

src/lib.rs

@@ -97,6 +97,14 @@ pub fn eval_mem<'a>(bf_str: &&str, mem: &'a mut [u8], pointer: &mut usize) -> Re
         }
         if char == '+' {
             if mem[*pointer] == 255 {
+
+                #[cfg(feature = "safe-eval")]
+                {
+                    return Err(
+                        BrainFuckError::new(format!("Attempt to overflow more than 255 ({})", pos), mem)
+                    );
+                }
+
                 mem[*pointer] = 0;
                 continue
             }
@@ -105,6 +113,14 @@ pub fn eval_mem<'a>(bf_str: &&str, mem: &'a mut [u8], pointer: &mut usize) -> Re
         }
         if char == '-' {
             if mem[*pointer] == 0 {
+
+                #[cfg(feature = "safe-eval")]
+                {
+                    return Err(
+                        BrainFuckError::new(format!("Attempt to overflow more than 255 ({})", pos), mem)
+                    );
+                }
+
                 mem[*pointer] = 255;
                 continue
             }