diff --git a/kernel/syscall/fs.rs b/kernel/syscall/fs.rs
index 3a23b6c..353a1b4 100644
--- a/kernel/syscall/fs.rs
+++ b/kernel/syscall/fs.rs
@@ -8,33 +8,23 @@ use super::{Error, Result};
 /// Read syscall
 pub fn read(fd: usize, buf: &mut [u8]) -> Result<usize> {
     println!("Read {}: {:X} {}", fd, buf.as_ptr() as usize, buf.len());
-    if let Some(context_lock) = context::contexts().current() {
-        let context = context_lock.read();
-        if let Some(file) = context.files.get(fd) {
-            println!("{:?}", file);
-            Ok(0)
-        } else {
-            Err(Error::BadFile)
-        }
-    } else {
-        Err(Error::NoProcess)
-    }
+    let contexts = context::contexts();
+    let context_lock = contexts.current().ok_or(Error::NoProcess)?;
+    let context = context_lock.read();
+    let file = context.files.get(fd).ok_or(Error::BadFile)?;
+    println!("{:?}", file);
+    Ok(0)
 }
 
 /// Write syscall
 pub fn write(fd: usize, buf: &[u8]) -> Result<usize> {
     println!("Write {}: {:X} {}", fd, buf.as_ptr() as usize, buf.len());
-    if let Some(context_lock) = context::contexts().current() {
-        let context = context_lock.read();
-        if let Some(file) = context.files.get(fd) {
-            println!("{:?}: {:?}", file, ::core::str::from_utf8(buf));
-            Ok(buf.len())
-        } else {
-            Err(Error::BadFile)
-        }
-    } else {
-        Err(Error::NoProcess)
-    }
+    let contexts = context::contexts();
+    let context_lock = contexts.current().ok_or(Error::NoProcess)?;
+    let context = context_lock.read();
+    let file = context.files.get(fd).ok_or(Error::BadFile);
+    println!("{:?}: {:?}", file, ::core::str::from_utf8(buf));
+    Ok(buf.len())
 }
 
 /// Open syscall
@@ -45,31 +35,20 @@ pub fn open(path: &[u8], flags: usize) -> Result<usize> {
     println!("Open namespace {:?} reference {:?}: {:X}", namespace_opt.map(::core::str::from_utf8), reference_opt.map(::core::str::from_utf8), flags);
 
     let file = {
-        if let Some(namespace) = namespace_opt {
-            let schemes = scheme::schemes();
-            if let Some(scheme_mutex) = schemes.get(namespace) {
-                scheme_mutex.lock().open(reference_opt.unwrap_or(b""), flags)
-            } else {
-                Err(Error::NoEntry)
-            }
-        } else {
-            Err(Error::NoEntry)
-        }
-    }?;
+        let namespace = namespace_opt.ok_or(Error::NoEntry)?;
+        let schemes = scheme::schemes();
+        let scheme_mutex = schemes.get(namespace).ok_or(Error::NoEntry)?;
+        let file = scheme_mutex.lock().open(reference_opt.unwrap_or(b""), flags)?;
+        file
+    };
 
-    if let Some(context_lock) = context::contexts().current() {
-        let mut context = context_lock.write();
-        if let Some(fd) = context.add_file(::context::file::File {
-            scheme: 0,
-            number: file
-        }) {
-            Ok(fd)
-        } else {
-            Err(Error::TooManyFiles)
-        }
-    } else {
-        Err(Error::NoProcess)
-    }
+    let contexts = context::contexts();
+    let context_lock = contexts.current().ok_or(Error::NoProcess)?;
+    let mut context = context_lock.write();
+    context.add_file(::context::file::File {
+        scheme: 0,
+        number: file
+    }).ok_or(Error::TooManyFiles)
 }
 
 /// Close syscall
diff --git a/kernel/syscall/process.rs b/kernel/syscall/process.rs
index 4f43aee..9db0bfa 100644
--- a/kernel/syscall/process.rs
+++ b/kernel/syscall/process.rs
@@ -23,10 +23,8 @@ pub fn exec(path: &[u8], args: &[[usize; 2]]) -> Result<usize> {
 }
 
 pub fn getpid() -> Result<usize> {
-    if let Some(context_lock) = context::contexts().current() {
-        let context = context_lock.read();
-        Ok(context.id)
-    } else {
-        Err(Error::NoProcess)
-    }
+    let contexts = context::contexts();
+    let context_lock = contexts.current().ok_or(Error::NoProcess)?;
+    let context = context_lock.read();
+    Ok(context.id)
 }