diff --git a/src/parser.rs b/src/parser.rs
index b97b636..d4fbb3e 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -30,16 +30,13 @@ pub enum Token {
 	/// PreGroups aren't needed once we have a tree.
 	PreGroup(LineLocation, VecDeque<Token>),
 
-	PreNegative(LineLocation),
-	PreFactorial(LineLocation),
-
 	Number(LineLocation, f64),
 	Multiply(VecDeque<Token>),
 	Divide(VecDeque<Token>),
 	Add(VecDeque<Token>),
 	Subtract(VecDeque<Token>),
-	//Factorial(VecDeque<Token>),
-	//Negative(VecDeque<Token>),
+	Factorial(VecDeque<Token>),
+	Negative(VecDeque<Token>),
 	Power(VecDeque<Token>),
 	Modulo(VecDeque<Token>),
 }
@@ -50,15 +47,17 @@ pub enum Token {
 #[derive(Debug)]
 #[derive(Copy, Clone)]
 pub enum Operators {
-	Null = 0,
-	ModuloLong, // Mod invoked with "mod"
+	ModuloLong = 0, // Mod invoked with "mod"
 	Subtract,
 	Add,
 	Divide,
 	Multiply,
 	ImplicitMultiply,
 	Modulo, // Mod invoked with %
-	Power
+	Power,
+
+	Negative,
+	Factorial
 }
 
 /// Specifies the location of a token in an input string.
diff --git a/src/parser/tokenize.rs b/src/parser/tokenize.rs
index d049454..b3f1daa 100644
--- a/src/parser/tokenize.rs
+++ b/src/parser/tokenize.rs
@@ -13,9 +13,7 @@ fn update_line_location(mut t: Token, stop_i: usize) -> Token {
 		Token::PreGroup(ref mut l, _) |
 		Token::PreOperator(ref mut l, _) |
 		Token::PreNumber(ref mut l, _) |
-		Token::PreWord(ref mut l, _) |
-		Token::PreNegative(ref mut l) |
-		Token::PreFactorial(ref mut l)
+		Token::PreWord(ref mut l, _)
 		=> {
 			let LineLocation{pos, .. } = l;
 			*l = LineLocation{
@@ -45,12 +43,6 @@ fn lookback(
 		let a: Token = g.pop_back().unwrap();
 
 		match (&a, &b) {
-
-			( // Delete consecutive negatives
-				Token::PreNegative(_),
-				Token::PreNegative(_)
-			) => {},
-
 			// Insert ImplicitMultiply
 			(Token::PreGroup(_,_), Token::PreGroup(l ,_)) |
 			(Token::PreGroup(_,_), Token::Number(l,_)) |
@@ -66,11 +58,7 @@ fn lookback(
 			},
 
 			// The following are syntax errors
-			(Token::PreOperator(la,_), Token::PreOperator(lb,_)) |
-			(Token::Number(la, _), Token::Number(lb,_)) |
-			(Token::PreNegative(la), Token::PreOperator(lb,_)) |
-			(Token::PreOperator(la, _), Token::PreFactorial(lb)) |
-			(Token::PreNegative(la), Token::PreFactorial(lb))
+			(Token::Number(la, _), Token::Number(lb,_))
 			=> {
 				let LineLocation { pos: posa, .. } = *la;
 				let LineLocation { pos: posb, len: lenb } = *lb;
@@ -81,15 +69,11 @@ fn lookback(
 			}
 
 			// The following are fine
-			(Token::PreOperator(_,_), Token::PreNegative(_)) |
+			(Token::PreOperator(_,_), Token::PreOperator(_,_)) |
 			(Token::PreOperator(_,_), Token::Number(_,_)) |
 			(Token::Number(_,_), Token::PreOperator(_,_)) |
 			(Token::PreOperator(_,_), Token::PreGroup(_,_)) |
-			(Token::PreGroup(_,_), Token::PreOperator(_,_)) |
-			(Token::PreNegative(_), Token::PreGroup(_,_)) |
-			(Token::PreNegative(_), Token::Number(_,_)) |
-			(Token::PreGroup(_,_), Token::PreFactorial(_)) |
-			(Token::Number(_,_), Token::PreFactorial(_))
+			(Token::PreGroup(_,_), Token::PreOperator(_,_))
 			=> { g.push_back(a); g.push_back(b); },
 
 			// If we get this far, we found a Token
@@ -131,8 +115,6 @@ fn push_token(
 			},
 			Token::PreOperator(_, _) => t,
 			Token::PreGroup(_, _) => t,
-			Token::PreNegative(_) => t,
-			Token::PreFactorial(_) => t,
 			_ => panic!()
 		});
 
@@ -160,7 +142,10 @@ pub fn tokenize(input: &String) -> Result<Token, (LineLocation, ParserError)> {
 		match c {
 			'!' => {
 				push_token(g_now, i, t)?;
-				t = Some(Token::PreFactorial(LineLocation{pos: i, len: 1}));
+				t = Some(Token::PreOperator(
+					LineLocation{pos: i, len: 1},
+					Operators::Factorial
+				));
 			},
 
 			// The minus sign can be both a Negative and an Operator.
@@ -181,7 +166,10 @@ pub fn tokenize(input: &String) -> Result<Token, (LineLocation, ParserError)> {
 
 					// Otherwise, this is a negative sign.
 					_ => {
-						t = Some(Token::PreNegative(LineLocation{pos: i, len: 1}));
+						t = Some(Token::PreOperator(
+							LineLocation{pos: i, len: 1},
+							Operators::Negative
+						));
 					}
 				};
 			},
diff --git a/src/parser/treeify.rs b/src/parser/treeify.rs
index 9e1a9d5..69fdbdf 100644
--- a/src/parser/treeify.rs
+++ b/src/parser/treeify.rs
@@ -5,49 +5,103 @@ use crate::parser::LineLocation;
 use crate::parser::ParserError;
 use crate::parser::Operators;
 
-
-pub fn treeify(
-	g: &mut Token,
-) -> Result<(), (LineLocation, ParserError)> {
-
-	let g_inner: &mut VecDeque<Token> = match g {
-		Token::PreGroup(_, ref mut x) => x,
+#[inline(always)]
+fn get_line_location(t: &Token) -> &LineLocation {
+	match t {
+		Token::PreNumber(l, _) |
+		Token::PreWord(l, _) |
+		Token::PreOperator(l, _) |
+		Token::PreGroup(l, _)
+		=> l,
 		_ => panic!()
+	}
+}
+
+#[inline(always)]
+fn select_op(k: Operators, new_token_args: VecDeque<Token>) -> Token {
+	match k {
+		Operators::Subtract => Token::Subtract(new_token_args),
+		Operators::Add => Token::Add(new_token_args),
+		Operators::Divide => Token::Divide(new_token_args),
+		Operators::Multiply => Token::Multiply(new_token_args),
+		Operators::ImplicitMultiply => Token::Multiply(new_token_args),
+		Operators::Modulo => Token::Modulo(new_token_args),
+		Operators::ModuloLong => Token::Modulo(new_token_args),
+		Operators::Power => Token::Power(new_token_args),
+		Operators::Negative => Token::Negative(new_token_args),
+		Operators::Factorial => Token::Factorial(new_token_args)
+	}
+}
+
+fn treeify_binary(
+	mut i: usize,
+	g_inner: &mut VecDeque<Token>
+) -> Result<usize, (LineLocation, ParserError)> {
+
+	let this: &Token = &g_inner[i];
+	let right: &Token = {
+		if i < g_inner.len()-1 {
+			&g_inner[i+1]
+		} else {
+			// This binary operator is at the end of the expression.
+			let l = match this {
+				Token::PreOperator(l, _) => l,
+				_ => panic!()
+			};
+			return Err((*l, ParserError::Syntax));
+		}
 	};
 
-	let mut i = 1;
-	while g_inner.len() > 1 {
 
-		let a: isize;
-		if i == 1 {
-			a = Operators::Null as isize;
-		} else {
-			let q: Operators = match g_inner[i-2] {
-				Token::PreOperator(_, x) => x,
-				_ => panic!()
-			};
-			a = q as isize;
-		}
+	if let Token::PreOperator(l, o) = right {
+		match o {
+			// Binary operators
+			Operators::ModuloLong |
+			Operators::Subtract |
+			Operators::Add |
+			Operators::Divide |
+			Operators::Multiply |
+			Operators::ImplicitMultiply |
+			Operators::Modulo |
+			Operators::Power |
+			// Right unary operators
+			Operators::Factorial
+			=> {
+				// Binary and right-unary operators cannot
+				// follow a binary operator.
+				let LineLocation { pos: posa, .. } = *get_line_location(&this);
+				let LineLocation { pos: posb, len: lenb } = *l;
+				return Err((
+					LineLocation{pos: posa, len: posb - posa + lenb},
+					ParserError::Syntax
+				));
+			},
 
-		let b: isize = match g_inner[i] {
-			Token::PreOperator(_, x) => x,
+			// Left unary operators
+			Operators::Negative => {
+				i += 1;
+				return Ok(i);
+			}
+		};
+	} else {
+
+		// Precedence of this operator
+		let this_val: isize = match this {
+			Token::PreOperator(_, q) => *q as isize,
 			_ => panic!()
-		} as isize;
+		};
 
-		let c: isize;
-		if i >= g_inner.len()-2 {
-			c = Operators::Null as isize;
-		} else {
-			let q: Operators = match g_inner[i+2] {
-				Token::PreOperator(_, x) => x,
+		// Precedence of the operator contesting the right argument.
+		let right_val = if i < g_inner.len()-2 {
+			match &g_inner[i+2] {
+				Token::PreOperator(_, q) => Some(*q as isize),
 				_ => panic!()
-			};
-			c = q as isize;
-		}
+			}
+		} else { None };
 
-		println!("{}, {:?}", i, g_inner);
-		if b >= a && b >= c {
-			// This operator owns both its arguments.
+
+		if right_val.is_none() || this_val > right_val.unwrap() {
+			// This operator has higher precedence, it takes both arguments
 			let left = g_inner.remove(i-1).unwrap();
 			let this = g_inner.remove(i-1).unwrap();
 			let right = g_inner.remove(i-1).unwrap();
@@ -61,27 +115,245 @@ pub fn treeify(
 			new_token_args.push_back(left);
 			new_token_args.push_back(right);
 
-			g_inner.insert(
-				i-1,
-				match k {
-					Operators::Subtract => Token::Subtract(new_token_args),
-					Operators::Add => Token::Add(new_token_args),
-					Operators::Divide => Token::Divide(new_token_args),
-					Operators::Multiply => Token::Multiply(new_token_args),
-					Operators::ImplicitMultiply => Token::Multiply(new_token_args),
-					Operators::Modulo => Token::Modulo(new_token_args),
-					Operators::ModuloLong => Token::Modulo(new_token_args),
-					Operators::Power => Token::Power(new_token_args),
-					Operators::Null => panic!()
-				}
-			);
-			if i >= 3 { i -= 2; }
+			g_inner.insert(i-1, select_op(k, new_token_args));
+
+			if i > 1 { i -= 2; } else { i = 0; }
+			return Ok(i);
 		} else {
-			// This operator has lower precedence than another.
-			// skip it for now.
+			// The operator to the right has higher precedence.
+			// Move on, don't to anything yet.
 			i += 2;
+			return Ok(i);
+		};
+	};
+}
+
+
+fn treeify_unaryleft(
+	mut i: usize,
+	g_inner: &mut VecDeque<Token>
+) -> Result<usize, (LineLocation, ParserError)> {
+
+	let this: &Token = &g_inner[i];
+	let right: &Token = {
+		if i < g_inner.len()-1 {
+			&g_inner[i+1]
+		} else {
+			let l = match this {
+				Token::PreOperator(l, _) => l,
+				_ => panic!()
+			};
+			return Err((*l, ParserError::Syntax));
+		}
+	};
+
+
+	if let Token::PreOperator(l, o) = right {
+		match o {
+			// Binary operators
+			Operators::ModuloLong |
+			Operators::Subtract |
+			Operators::Add |
+			Operators::Divide |
+			Operators::Multiply |
+			Operators::ImplicitMultiply |
+			Operators::Modulo |
+			Operators::Power |
+			// Right unary operators
+			Operators::Factorial
+			=> {
+				// Binary and right-unary operators cannot
+				// follow a binary operator.
+				let LineLocation { pos: posa, .. } = *get_line_location(&this);
+				let LineLocation { pos: posb, len: lenb } = *l;
+				return Err((
+					LineLocation{pos: posa, len: posb - posa + lenb},
+					ParserError::Syntax
+				));
+			},
+
+			// Left unary operators
+			Operators::Negative => {
+				i += 1;
+				return Ok(i);
+			}
+		};
+	} else {
+
+		// Precedence of this operator
+		let this_val: isize = match this {
+			Token::PreOperator(_, q) => *q as isize,
+			_ => panic!()
+		};
+
+		// Precedence of the operator contesting its argument
+		let right_val = if i < g_inner.len()-2 {
+			match &g_inner[i+2] {
+				Token::PreOperator(_, q) => Some(*q as isize),
+				_ => panic!()
+			}
+		} else { None };
+
+
+		if right_val.is_none() || this_val > right_val.unwrap() {
+			let this = g_inner.remove(i).unwrap();
+			let right = g_inner.remove(i).unwrap();
+
+			let k = match this {
+				Token::PreOperator(_, k) => k,
+				_ => panic!()
+			};
+
+			let mut new_token_args: VecDeque<Token> = VecDeque::with_capacity(3);
+			new_token_args.push_back(right);
+
+			g_inner.insert(i, select_op(k, new_token_args));
+
+			if i > 0 { i -= 1; } else { i = 0; }
+			return Ok(i);
+		} else {
+			// The operator to the right has higher precedence.
+			// Move on, don't to anything yet.
+			i += 2;
+			return Ok(i);
+		};
+	};
+}
+
+fn treeify_unaryright(
+	mut i: usize,
+	g_inner: &mut VecDeque<Token>
+) -> Result<usize, (LineLocation, ParserError)> {
+
+	let this: &Token = &g_inner[i];
+	let left: &Token = {
+		if i > 0 {
+			&g_inner[i-1]
+		} else {
+			let l = match this {
+				Token::PreOperator(l, _) => l,
+				_ => panic!()
+			};
+			return Err((*l, ParserError::Syntax));
+		}
+	};
+
+
+	// We need to check the element after unary right operators too.
+	// Bad syntax like `3!3` won't be caught otherwise.
+	let right: Option<&Token> = {
+		if i < g_inner.len()-1 {
+			Some(&g_inner[i+1])
+		} else {None}
+	};
+
+	if right.is_some() {
+		if let Token::PreOperator(l, o) = right.unwrap() {
+			match o {
+				// Left unary operators
+				Operators::Negative => {
+					let LineLocation { pos: posa, .. } = *get_line_location(&this);
+					let LineLocation { pos: posb, len: lenb } = *l;
+					return Err((
+						LineLocation{pos: posa, len: posb - posa + lenb},
+						ParserError::Syntax
+					));
+				},
+				_ => {},
+			};
+		} else {
+			return Err((
+				*get_line_location(&this),
+				ParserError::Syntax
+			));
 		}
-		println!("{}", i);
 	}
+
+	if let Token::PreOperator(l, _) = left {
+		let LineLocation { pos: posa, .. } = *get_line_location(&this);
+		let LineLocation { pos: posb, len: lenb } = *l;
+		return Err((
+			LineLocation{pos: posa, len: posb - posa + lenb},
+			ParserError::Syntax
+		));
+
+	} else {
+
+		// Precedence of this operator
+		let this_val: isize = match this {
+			Token::PreOperator(_, q) => *q as isize,
+			_ => panic!()
+		};
+
+		// Precedence of the operator contesting its argument.
+		let left_val = if i >= 2 {
+			match &g_inner[i-2] {
+				Token::PreOperator(_, q) => Some(*q as isize),
+				_ => panic!()
+			}
+		} else { None };
+
+
+		if left_val.is_none() || this_val > left_val.unwrap() {
+			let this = g_inner.remove(i).unwrap();
+			let left = g_inner.remove(i-1).unwrap();
+
+			let k = match this {
+				Token::PreOperator(_, k) => k,
+				_ => panic!()
+			};
+
+			let mut new_token_args: VecDeque<Token> = VecDeque::with_capacity(3);
+			new_token_args.push_back(left);
+
+			g_inner.insert(i-1, select_op(k, new_token_args));
+
+			if i > 2 { i -= 2; } else { i = 0; }
+			return Ok(i);
+		} else {
+			// The operator to the right has higher precedence.
+			// Move on, don't to anything yet.
+			i += 1;
+			return Ok(i);
+		};
+	};
+}
+
+pub fn treeify(
+	g: &mut Token,
+) -> Result<(), (LineLocation, ParserError)> {
+
+	let g_inner: &mut VecDeque<Token> = match g {
+		Token::PreGroup(_, ref mut x) => x,
+		_ => panic!()
+	};
+
+	let mut i: usize = 0;
+	while g_inner.len() > 1 {
+		let this_op = match &g_inner[i] {
+			Token::PreOperator(_, o) => o,
+			_ => { i+=1; continue; }
+		};
+
+		match this_op {
+			Operators::ModuloLong |
+			Operators::Subtract |
+			Operators::Add |
+			Operators::Divide |
+			Operators::Multiply |
+			Operators::ImplicitMultiply |
+			Operators::Modulo |
+			Operators::Power
+			=> { i = treeify_binary(i, g_inner)?; },
+
+			Operators::Negative
+			=> { i = treeify_unaryleft(i, g_inner)?; },
+
+			Operators::Factorial
+			=> { i = treeify_unaryright(i, g_inner)?; }
+
+		};
+	}
+
 	return Ok(());
 }
\ No newline at end of file