feat: utils: add Then for bool type

kernel/src/utils/mod.rs

@@ -1,3 +1,4 @@
 pub mod extern_addr;
 pub mod function_name;
 pub mod size;
+pub mod then;

kernel/src/utils/then.rs

@@ -0,0 +1,23 @@
+pub trait Then {
+    fn and<T, E, F: FnOnce() -> Result<T, E>>(self, f: F, err: E) -> Result<T, E>;
+    fn some<T, E, F: FnOnce() -> T>(self, f: F, err: E) -> Result<T, E>;
+}
+
+impl Then for bool {
+    #[inline]
+    fn and<T, E, F: FnOnce() -> Result<T, E>>(self, f: F, err: E) -> Result<T, E> {
+        if self {
+            f()
+        } else {
+            Err(err)
+        }
+    }
+
+    fn some<T, E, F: FnOnce() -> T>(self, f: F, err: E) -> Result<T, E> {
+        if self {
+            Ok(f())
+        } else {
+            Err(err)
+        }
+    }
+}

kernel/src/vspace/allocator/freelist.rs

@@ -105,8 +105,8 @@ impl FreeList {
     }
 
     pub fn reserve(&mut self, start: PhysAddr, size: usize) {
-        if let Some((region, _)) = self
+        if let Some((region, _)) =
-            .alloc_node(|region| (region.start_addr() <= start).chain(|| region.fit(size, 1), ()))
+            self.alloc_node(|region| (region.start_addr() <= start).and(|| region.fit(size, 1), ()))
         {
             /* layout
              * region: | before | [start +: size] | after |