diff --git a/dust-lang/src/abstract_tree/type.rs b/dust-lang/src/abstract_tree/type.rs
index 3cd04ff..b110ce5 100644
--- a/dust-lang/src/abstract_tree/type.rs
+++ b/dust-lang/src/abstract_tree/type.rs
@@ -113,7 +113,18 @@ impl Type {
                     return_type: right_return,
                 },
             ) => {
-                if left_return == right_return && left_parameters == right_parameters {
+                if left_return.node == right_return.node {
+                    for (left_parameter, right_parameter) in
+                        left_parameters.iter().zip(right_parameters.iter())
+                    {
+                        if left_parameter.node != right_parameter.node {
+                            return Err(TypeConflict {
+                                actual: other.clone(),
+                                expected: self.clone(),
+                            });
+                        }
+                    }
+
                     return Ok(());
                 }
             }
diff --git a/dust-lang/src/lib.rs b/dust-lang/src/lib.rs
index f9cc274..08e1e3c 100644
--- a/dust-lang/src/lib.rs
+++ b/dust-lang/src/lib.rs
@@ -19,7 +19,8 @@ pub use value::Value;
 pub fn interpret<'src>(source_id: &str, source: &str) -> Result<Option<Value>, InterpreterError> {
     let mut interpreter = Interpreter::new(Context::new());
 
-    interpreter.run(Rc::new(source_id.to_string()), Rc::from(source))
+    interpreter.load_std()?;
+    interpreter.run(Rc::from(source_id), Rc::from(source))
 }
 
 pub fn interpret_without_std(
@@ -28,12 +29,12 @@ pub fn interpret_without_std(
 ) -> Result<Option<Value>, InterpreterError> {
     let mut interpreter = Interpreter::new(Context::new());
 
-    interpreter.run(Rc::new(source_id.to_string()), Rc::from(source))
+    interpreter.run(Rc::from(source_id.to_string()), Rc::from(source))
 }
 
 pub struct Interpreter {
     context: Context,
-    sources: Rc<RefCell<Vec<(Rc<String>, Rc<str>)>>>,
+    sources: Rc<RefCell<Vec<(Rc<str>, Rc<str>)>>>,
 }
 
 impl Interpreter {
@@ -46,7 +47,7 @@ impl Interpreter {
 
     pub fn run(
         &mut self,
-        source_id: Rc<String>,
+        source_id: Rc<str>,
         source: Rc<str>,
     ) -> Result<Option<Value>, InterpreterError> {
         let tokens = lex(source.as_ref()).map_err(|errors| InterpreterError {
@@ -69,7 +70,7 @@ impl Interpreter {
         Ok(value_option)
     }
 
-    pub fn run_all<T: IntoIterator<Item = (Rc<String>, Rc<str>)>>(
+    pub fn run_all<T: IntoIterator<Item = (Rc<str>, Rc<str>)>>(
         &mut self,
         sources: T,
     ) -> Result<Option<Value>, InterpreterError> {
@@ -85,24 +86,24 @@ impl Interpreter {
     pub fn load_std(&mut self) -> Result<Option<Value>, InterpreterError> {
         self.run_all([
             (
-                Rc::new("std/io.ds".to_string()),
+                Rc::from("std/io.ds"),
                 Rc::from(include_str!("../../std/io.ds")),
             ),
             (
-                Rc::new("std/thread.ds".to_string()),
+                Rc::from("std/thread.ds"),
                 Rc::from(include_str!("../../std/thread.ds")),
             ),
         ])
     }
 
-    pub fn sources(&self) -> vec::IntoIter<(Rc<String>, Rc<str>)> {
+    pub fn sources(&self) -> vec::IntoIter<(Rc<str>, Rc<str>)> {
         self.sources.borrow().clone().into_iter()
     }
 }
 
 #[derive(Debug, PartialEq)]
 pub struct InterpreterError {
-    source_id: Rc<String>,
+    source_id: Rc<str>,
     errors: Vec<Error>,
 }
 
@@ -113,7 +114,7 @@ impl InterpreterError {
 }
 
 impl InterpreterError {
-    pub fn build_reports<'a>(self) -> Vec<Report<'a, (Rc<String>, Range<usize>)>> {
+    pub fn build_reports<'a>(self) -> Vec<Report<'a, (Rc<str>, Range<usize>)>> {
         let mut reports = Vec::new();
 
         for error in self.errors {
diff --git a/dust-shell/src/cli.rs b/dust-shell/src/cli.rs
index 48a1c52..e6b2ba2 100644
--- a/dust-shell/src/cli.rs
+++ b/dust-shell/src/cli.rs
@@ -80,8 +80,7 @@ pub fn run_shell(context: Context) -> Result<(), io::Error> {
                     continue;
                 }
 
-                let run_result =
-                    interpreter.run(Rc::new("input".to_string()), Rc::from(buffer.as_str()));
+                let run_result = interpreter.run(Rc::from("input"), Rc::from(buffer.as_str()));
 
                 match run_result {
                     Ok(Some(value)) => {
diff --git a/dust-shell/src/main.rs b/dust-shell/src/main.rs
index cb07177..e9b4cd5 100644
--- a/dust-shell/src/main.rs
+++ b/dust-shell/src/main.rs
@@ -49,9 +49,9 @@ fn main() {
     let (source_id, source) = if let Some(path) = args.path {
         let source = read_to_string(&path).unwrap();
 
-        (Rc::new(path.to_string()), source)
+        (Rc::from(path), source)
     } else if let Some(command) = args.command {
-        (Rc::new("input".to_string()), command)
+        (Rc::from("input"), command)
     } else {
         match run_shell(context) {
             Ok(_) => {}
diff --git a/std/io.ds b/std/io.ds
index 3659f1e..b47d873 100644
--- a/std/io.ds
+++ b/std/io.ds
@@ -3,7 +3,7 @@ io = {
 		__READ_LINE__()
 	}
 
-	write_line = (T)(output: T) none {
+	write_line = (output: str) none {
 		__WRITE_LINE__(output)
 	}
 }