src/scanner/macros.rs

@@ -5,4 +5,59 @@ macro_rules! advance {
 
         $buffer = rest
     };
+    (<- $buffer:expr, $amount:expr) => {{
+        let (cut, rest) = $buffer.split_at($amount);
+
+        $buffer = rest;
+
+        cut
+    }};
+}
+
+/// New cow pointer from the given expr
+macro_rules! cow {
+    ($from:expr) => {
+        std::borrow::Cow::from($from)
+    };
+}
+
+/// Check the buffer for $byte matches at $pos, optionally
+/// returning an error Note that the error path is special
+/// cased to return an UnexpectedEOF if it encounters an
+/// empty slice
+macro_rules! check {
+    ($buffer:expr, $(@$pos:expr,)? is $( $byte:pat )|+ $(, else $error:expr)? ) => {
+        {
+            let b = match $buffer$([$pos..])? {
+                [] => Err(false),
+                $([$byte, ..])|+ => Ok(true),
+                _ => Ok(false)
+            };
+
+            check!(@priv b $(=> $error)? )
+        }
+    };
+    ($buffer:expr, $(@$pos:expr,)? not $( $byte:pat )|+ $(, else $error:expr)? ) => {
+        {
+            let b = match $buffer$([$pos..])? {
+                [] => Err(true),
+                $([$byte, ..])|+ => Ok(false),
+                _ => Ok(true)
+            };
+
+            check!(@priv b $(=> $error)? )
+        }
+    };
+    (@priv $bool:expr) => {
+        match $bool {
+            Ok(b) | Err(b) => b
+        }
+    };
+    (@priv $bool:expr => $error:expr) => {
+        match $bool {
+            Ok(true) => Ok(()),
+            Ok(false) => Err($error),
+            Err(_) => Err($crate::scanner::error::ScanError::UnexpectedEOF),
+        }
+    }
 }

src/scanner/tests/macros.rs

@@ -63,9 +63,3 @@ macro_rules! tokens {
         assert_eq!(event, $expected, $msg)
     };
 }
-
-macro_rules! cow {
-    ($literal:expr) => {
-        std::borrow::Cow::from($literal)
-    };
-}