diff --git a/schala-lang/language/src/ast.rs b/schala-lang/language/src/ast.rs
index e0ccc79..a8e73a5 100644
--- a/schala-lang/language/src/ast.rs
+++ b/schala-lang/language/src/ast.rs
@@ -1,10 +1,12 @@
 use std::rc::Rc;
 use std::convert::From;
-use std::str::FromStr;
 
-use crate::builtin::{BinOp, Builtin};
+use crate::builtin::{BinOp};
 use crate::typechecking::TypeData;
 
+mod operators;
+pub use operators::*;
+
 #[derive(Clone, Debug, PartialEq)]
 pub struct Meta<T> {
   n: T,
@@ -242,30 +244,3 @@ pub enum ForBody {
   MonadicReturn(Meta<Expression>),
   StatementBlock(Block),
 }
-
-#[derive(Debug, PartialEq, Clone)]
-pub struct PrefixOp {
-  pub sigil: Rc<String>,
-  pub builtin: Option<Builtin>,
-}
-
-impl PrefixOp {
-  pub fn from_sigil(sigil: &str) -> PrefixOp {
-    PrefixOp {
-      sigil: Rc::new(sigil.to_string()),
-      builtin: Builtin::from_str(sigil).ok(),
-    }
-  }
-  pub fn sigil(&self) -> &Rc<String> {
-    &self.sigil
-  }
-  pub fn is_prefix(op: &str) -> bool {
-    match op {
-      "+" => true,
-      "-" => true,
-      "!" => true,
-      _ => false
-    }
-  }
-}
-
diff --git a/schala-lang/language/src/ast/operators.rs b/schala-lang/language/src/ast/operators.rs
new file mode 100644
index 0000000..64f4e2c
--- /dev/null
+++ b/schala-lang/language/src/ast/operators.rs
@@ -0,0 +1,41 @@
+use std::rc::Rc;
+use std::str::FromStr;
+
+use crate::builtin::Builtin;
+
+#[derive(Debug, PartialEq, Clone)]
+pub struct PrefixOp {
+  pub sigil: Rc<String>,
+  pub builtin: Option<Builtin>,
+}
+
+impl PrefixOp {
+  pub fn sigil(&self) -> &Rc<String> {
+    &self.sigil
+  }
+  pub fn is_prefix(op: &str) -> bool {
+    match op {
+      "+" => true,
+      "-" => true,
+      "!" => true,
+      _ => false
+    }
+  }
+}
+
+impl FromStr for PrefixOp {
+  type Err = ();
+
+  fn from_str(s: &str) -> Result<Self, Self::Err> {
+    use Builtin::*;
+
+    let builtin = match s {
+      "+" => Ok(Increment),
+      "-" => Ok(Negate),
+      "!" => Ok(BooleanNot),
+      _ => Err(())
+    };
+
+    builtin.map(|builtin| PrefixOp { sigil: Rc::new(s.to_string()), builtin: Some(builtin) })
+  }
+}
diff --git a/schala-lang/language/src/builtin.rs b/schala-lang/language/src/builtin.rs
index 2d8c080..fcbf97d 100644
--- a/schala-lang/language/src/builtin.rs
+++ b/schala-lang/language/src/builtin.rs
@@ -8,7 +8,9 @@ use crate::typechecking::{TypeConst, Type};
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Builtin {
   Add,
+  Increment,
   Subtract,
+  Negate,
   Multiply,
   Divide,
   Quotient,
@@ -61,6 +63,8 @@ impl Builtin {
       IOGetLine => ty!(StringT),
       Assignment => ty!(Unit),
       Concatenate => ty!(StringT -> StringT -> StringT),
+      Increment => ty!(Nat -> Int),
+      Negate => ty!(Nat -> Int)
     }
   }
 }
diff --git a/schala-lang/language/src/eval.rs b/schala-lang/language/src/eval.rs
index 73bd769..d78ab62 100644
--- a/schala-lang/language/src/eval.rs
+++ b/schala-lang/language/src/eval.rs
@@ -327,10 +327,10 @@ impl<'a> State<'a> {
       /* prefix ops */
       (BooleanNot, &[Lit(Bool(true))]) => Lit(Bool(false)),
       (BooleanNot, &[Lit(Bool(false))]) => Lit(Bool(true)),
-      (Subtract, &[Lit(Nat(n))]) => Lit(Int(-1*(n as i64))),
-      (Subtract, &[Lit(Int(n))]) => Lit(Int(-1*(n as i64))),
-      (Add, &[Lit(Int(n))]) => Lit(Int(n)),
-      (Add, &[Lit(Nat(n))]) => Lit(Nat(n)),
+      (Negate, &[Lit(Nat(n))]) => Lit(Int(-1*(n as i64))),
+      (Negate, &[Lit(Int(n))]) => Lit(Int(-1*(n as i64))),
+      (Increment, &[Lit(Int(n))]) => Lit(Int(n)),
+      (Increment, &[Lit(Nat(n))]) => Lit(Nat(n)),
 
 
       /* builtin functions */
diff --git a/schala-lang/language/src/parsing.rs b/schala-lang/language/src/parsing.rs
index f446746..0b4e557 100644
--- a/schala-lang/language/src/parsing.rs
+++ b/schala-lang/language/src/parsing.rs
@@ -145,6 +145,7 @@
 mod test;
 
 use std::rc::Rc;
+use std::str::FromStr;
 
 use crate::tokenizing::*;
 use crate::tokenizing::Kw::*;
@@ -625,8 +626,9 @@ impl Parser {
           _ => unreachable!(),
         };
         let expr = self.primary()?;
+        let prefix_op = PrefixOp::from_str(sigil.as_str()).unwrap();
         Ok(Expression::new(
-          ExpressionKind::PrefixExp(PrefixOp::from_sigil(sigil.as_str()), bx!(expr.into()))
+          ExpressionKind::PrefixExp(prefix_op, bx!(expr.into()))
         ))
       },
       _ => self.call_expr()
diff --git a/schala-lang/language/src/parsing/test.rs b/schala-lang/language/src/parsing/test.rs
index 9e6d4a9..85806a5 100644
--- a/schala-lang/language/src/parsing/test.rs
+++ b/schala-lang/language/src/parsing/test.rs
@@ -1,5 +1,7 @@
 #![cfg(test)]
 use ::std::rc::Rc;
+use std::str::FromStr;
+
 use super::tokenize;
 use super::ParseResult;
 use crate::builtin::{BinOp};
@@ -59,7 +61,7 @@ macro_rules! binexp {
   ($op:expr, $lhs:expr, $rhs:expr) => { BinExp(BinOp::from_sigil($op), bx!(Expression::new($lhs).into()), bx!(Expression::new($rhs).into())) }
 }
 macro_rules! prefexp {
-  ($op:expr, $lhs:expr) => { PrefixExp(PrefixOp::from_sigil($op), bx!(Expression::new($lhs).into())) }
+  ($op:expr, $lhs:expr) => { PrefixExp(PrefixOp::from_str($op).unwrap(), bx!(Expression::new($lhs).into())) }
 }
 macro_rules! exst {
   ($expr_type:expr) => { Meta::new(Statement::ExpressionStatement(Expression::new($expr_type).into())) };