diff --git a/src/parser.rs b/src/parser.rs
index 34a35ab..42476cf 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -52,7 +52,6 @@ pub enum Token {
 }
 
 impl Token {
-
 	#[inline(always)]
 	pub fn get_args(&mut self) -> Option<&mut VecDeque<Token>> {
 		match self {
@@ -239,7 +238,78 @@ pub enum Operator {
 	Power,
 
 	Negative,
-	Factorial
+	Factorial,
+}
+
+impl Operator {
+	#[inline(always)]
+	pub fn is_binary(&self) -> bool {
+		match self {
+			Operator::Negative
+			| Operator::Factorial
+			=> false,
+			_ => true
+		}
+	}
+
+	#[inline(always)]
+	pub fn is_left_associative(&self) -> bool {
+		match self {
+			Operator::Negative
+			| Operator::Power
+			=> false,
+			_ => true
+		}
+	}
+
+	#[inline(always)]
+	pub fn into_token(&self, mut args: VecDeque<Token>) -> Token {
+		match self {
+			Operator::Add => Token::Add(args),
+
+			Operator::Multiply
+			| Operator::ImplicitMultiply
+			=> Token::Multiply(args),
+			
+			Operator::Subtract => {
+				if args.len() != 2 { panic!() }
+				let a = args.pop_front().unwrap();
+				let b = args.pop_front().unwrap();
+	
+				Token::Add(
+				VecDeque::from(vec!(
+						a,
+						Token::Negative(VecDeque::from(vec!(b)))
+				)))
+			},
+
+			Operator::Divide => {
+				if args.len() != 2 { panic!() }
+				Token::Divide(args)
+			},
+	
+			Operator::ModuloLong |
+			Operator::Modulo => {
+				if args.len() != 2 { panic!() }
+				Token::Modulo(args)
+			},
+	
+			Operator::Power => {
+				if args.len() != 2 { panic!() }
+				Token::Power(args)
+			},
+
+			Operator::Negative => {
+				if args.len() != 1 { panic!() }
+				Token::Negative(args)
+			},
+
+			Operator::Factorial => {
+				if args.len() != 1 { panic!() }
+				Token::Factorial(args)
+			}
+		}
+	}
 }
 
 /// Specifies the location of a token in an input string.
diff --git a/src/parser/treeify.rs b/src/parser/treeify.rs
index 67c90af..535f220 100644
--- a/src/parser/treeify.rs
+++ b/src/parser/treeify.rs
@@ -5,35 +5,11 @@ use crate::parser::LineLocation;
 use crate::parser::ParserError;
 use crate::parser::Operator;
 
-#[inline(always)]
-fn select_op(k: Operator, mut new_token_args: VecDeque<Token>) -> Token {
-	match k {
-		Operator::Subtract => {
-			let a = new_token_args.pop_front().unwrap();
-			let b = new_token_args.pop_front().unwrap();
-
-			Token::Add(
-			VecDeque::from(vec!(
-					a,
-					Token::Negative(VecDeque::from(vec!(b)))
-			)))
-		},
-		Operator::Add => Token::Add(new_token_args),
-		Operator::Divide => Token::Divide(new_token_args),
-		Operator::Multiply => Token::Multiply(new_token_args),
-		Operator::ImplicitMultiply => Token::Multiply(new_token_args),
-		Operator::Modulo => Token::Modulo(new_token_args),
-		Operator::ModuloLong => Token::Modulo(new_token_args),
-		Operator::Power => Token::Power(new_token_args),
-		Operator::Negative => Token::Negative(new_token_args),
-		Operator::Factorial => Token::Factorial(new_token_args)
-	}
-}
-
 fn treeify_binary(
 	mut i: usize,
-	g_inner: &mut VecDeque<Token>
-) -> Result<usize, (LineLocation, ParserError)> {
+	g_inner: &mut VecDeque<Token>,
+	left_associative: bool
+) -> Result<(), (LineLocation, ParserError)> {
 
 	let this: &Token = &g_inner[i];
 
@@ -46,49 +22,50 @@ fn treeify_binary(
 		return Err((*l, ParserError::Syntax));
 	}
 
-	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
-			Operator::ModuloLong |
-			Operator::Subtract |
-			Operator::Add |
-			Operator::Divide |
-			Operator::Multiply |
-			Operator::ImplicitMultiply |
-			Operator::Modulo |
-			Operator::Power |
-			// Right unary operators
-			Operator::Factorial
-			=> {
-				// Binary and right-unary operators cannot
-				// follow a binary operator.
-				let tl = *this.get_line_location();
-				return Err((
-					LineLocation{pos: tl.pos, len: l.pos - tl.pos + l.len},
-					ParserError::Syntax
-				));
-			},
-
-			// Left unary operators
-			Operator::Negative => {
-				i += 1;
-				return Ok(i);
+	let next: &Token;
+	if left_associative {
+		next = {
+			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));
 			}
 		};
 	} else {
+		next = {
+			if i > 0 {
+				&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) = next {
+		if {
+			(!o.is_binary()) &&
+			!(o.is_left_associative() && left_associative)
+		} {
+			// Only right-associative unary operators can follow a binary operator
+			return Ok(());
+		} else {
+			let tl = *this.get_line_location();
+			return Err((
+				LineLocation{pos: tl.pos, len: l.pos - tl.pos + l.len},
+				ParserError::Syntax
+			));
+		}
+	} else {
 
 		// Precedence of this operator
 		let this_val: isize = match this {
@@ -96,7 +73,13 @@ fn treeify_binary(
 			_ => panic!()
 		};
 
-		// Precedence of the operator contesting the right argument.
+		// Precedence of the operators contesting our arguments
+		let left_val = if i > 1 {
+			match &g_inner[i-2] {
+				Token::PreOperator(_, q) => Some(*q as isize),
+				_ => panic!()
+			}
+		} else { None };
 		let right_val = if i < g_inner.len()-2 {
 			match &g_inner[i+2] {
 				Token::PreOperator(_, q) => Some(*q as isize),
@@ -104,8 +87,10 @@ fn treeify_binary(
 			}
 		} else { None };
 
-
-		if right_val.is_none() || this_val > right_val.unwrap() {
+		if {
+			(left_val.is_none() || this_val >= left_val.unwrap()) &&
+			(right_val.is_none() || this_val >= right_val.unwrap())
+		} {
 			// This operator has higher precedence, it takes both arguments
 			let mut left = g_inner.remove(i-1).unwrap();
 			let this = g_inner.remove(i-1).unwrap();
@@ -122,140 +107,63 @@ fn treeify_binary(
 			new_token_args.push_back(left);
 			new_token_args.push_back(right);
 
-			g_inner.insert(i-1, select_op(k, new_token_args));
+			g_inner.insert(i-1, k.into_token(new_token_args));
 
-			if i > 1 { i -= 2; } else { i = 0; }
-			return Ok(i);
+			return Ok(());
 		} else {
-			// The operator to the right has higher precedence.
-			// Move on, don't to anything yet.
-			i += 2;
-			return Ok(i);
+			return Ok(());
 		};
 	};
 }
 
 
-fn treeify_unaryleft(
-	mut i: usize,
-	g_inner: &mut VecDeque<Token>
-) -> Result<usize, (LineLocation, ParserError)> {
+fn treeify_unary(
+	i: usize,
+	g_inner: &mut VecDeque<Token>,
+	left_associative: bool
+) -> Result<(), (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
-			Operator::ModuloLong |
-			Operator::Subtract |
-			Operator::Add |
-			Operator::Divide |
-			Operator::Multiply |
-			Operator::ImplicitMultiply |
-			Operator::Modulo |
-			Operator::Power |
-			// Right unary operators
-			Operator::Factorial
-			=> {
-				// Binary and right-unary operators cannot
-				// follow a binary operator.
-				let tl = *this.get_line_location();
-				return Err((
-					LineLocation{pos: tl.pos, len: l.pos - tl.pos + l.len},
-					ParserError::Syntax
-				));
-			},
-
-			// Left unary operators
-			Operator::Negative => {
-				i += 1;
-				return Ok(i);
+	let next: &Token;
+	if left_associative {
+		next = {
+			if i > 0 {
+				&g_inner[i-1]
+			} else {
+				let l = match this {
+					Token::PreOperator(l, _) => l,
+					_ => panic!()
+				};
+				return Err((*l, 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 right_val = if i < g_inner.len()-2 {
-			match &g_inner[i+2] {
-				Token::PreOperator(_, q) => Some(*q as isize),
-				_ => panic!()
+		next = {
+			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));
 			}
-		} else { None };
-
-
-		if right_val.is_none() || this_val > right_val.unwrap() {
-			let this = g_inner.remove(i).unwrap();
-			let mut right = g_inner.remove(i).unwrap();
-			if let Token::PreGroup(_, _) = right { right = p_treeify(right)?; }
-
-			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.
+	// We need to check the element after unary 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}
-	};
+	let prev: Option<&Token>;
+	if left_associative {
+		prev = 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() {
+	} else {
+		prev = if i > 0 { Some(&g_inner[i-1]) } else {None};
+
+	}
+
+	if prev.is_some() {
+		if let Token::PreOperator(l, o) = prev.unwrap() {
 			match o {
 				// Left unary operators
 				Operator::Negative => {
@@ -275,13 +183,14 @@ fn treeify_unaryright(
 		}
 	}
 
-	if let Token::PreOperator(l, _) = left {
+
+
+	if let Token::PreOperator(l, _) = next {
 		let tl = *this.get_line_location();
 		return Err((
 			LineLocation{pos: tl.pos, len: l.pos - tl.pos + l.len},
 			ParserError::Syntax
 		));
-
 	} else {
 
 		// Precedence of this operator
@@ -290,19 +199,32 @@ fn treeify_unaryright(
 			_ => 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 };
+		// Precedence of the operator contesting its argument
+		let next_val = if left_associative {
+			if i > 1 {
+				match &g_inner[i-2] {
+					Token::PreOperator(_, q) => Some(*q as isize),
+					_ => panic!()
+				}
+			} else { None }
+		} else {
+			if i < g_inner.len()-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() {
+		if next_val.is_none() || this_val > next_val.unwrap() {
 			let this = g_inner.remove(i).unwrap();
-			let mut left = g_inner.remove(i-1).unwrap();
-			if let Token::PreGroup(_, _) = left { left = p_treeify(left)?; }
+			let mut next;
+			if left_associative {
+				next = g_inner.remove(i-1).unwrap();
+			} else {
+				next = g_inner.remove(i).unwrap();
+			}
+			if let Token::PreGroup(_, _) = next { next = p_treeify(next)?; }
 
 			let k = match this {
 				Token::PreOperator(_, k) => k,
@@ -310,17 +232,19 @@ fn treeify_unaryright(
 			};
 
 			let mut new_token_args: VecDeque<Token> = VecDeque::with_capacity(3);
-			new_token_args.push_back(left);
+			new_token_args.push_back(next);
 
-			g_inner.insert(i-1, select_op(k, new_token_args));
+			if left_associative {
+				g_inner.insert(i-1, k.into_token(new_token_args));
+			} else {
+				g_inner.insert(i, k.into_token(new_token_args));
+			}
 
-			if i > 2 { i -= 2; } else { i = 0; }
-			return Ok(i);
+			return Ok(());
 		} else {
 			// The operator to the right has higher precedence.
 			// Move on, don't to anything yet.
-			i += 1;
-			return Ok(i);
+			return Ok(());
 		};
 	};
 }
@@ -334,37 +258,52 @@ pub fn p_treeify(
 		_ => panic!()
 	};
 
-	let mut i: usize = 0;
+	let mut left_associative = true;
+	let mut j: i64 = 0;
 	while g_inner.len() > 1 {
+
+
+		if j <= -1 {
+			left_associative = true;
+			j = 0;
+		} else if j >= g_inner.len() as i64 {
+			left_associative = false;
+			j = (g_inner.len() - 1) as i64;
+		}
+
+		let i = j as usize;
 		let this_op = match &g_inner[i] {
 			Token::PreOperator(_, o) => o,
-			_ => { i+=1; continue; }
+			_ => {
+				if left_associative { j += 1 } else { j -= 1 };
+				continue;
+			}
 		};
 
-		match this_op {
-			Operator::ModuloLong |
-			Operator::Subtract |
-			Operator::Add |
-			Operator::Divide |
-			Operator::Multiply |
-			Operator::ImplicitMultiply |
-			Operator::Modulo |
-			Operator::Power
-			=> { i = treeify_binary(i, g_inner)?; },
-
-			Operator::Negative
-			=> { i = treeify_unaryleft(i, g_inner)?; },
-
-			Operator::Factorial
-			=> { i = treeify_unaryright(i, g_inner)?; }
-
-		};
+		if left_associative {
+			if this_op.is_left_associative() {
+				if this_op.is_binary() {
+					treeify_binary(i, g_inner, left_associative)?;
+				} else {
+					treeify_unary(i, g_inner, left_associative)?;
+				}
+			}
+			j += 1 
+		} else {
+			if !this_op.is_left_associative() {
+				if this_op.is_binary() {
+					treeify_binary(i, g_inner, left_associative)?;
+				} else {
+					treeify_unary(i, g_inner, left_associative)?;
+				}
+			}
+			j -= 1
+		}
 	}
 
 	g = g_inner.pop_front().unwrap();
 
-	// Catch the edge case where the entire group we're given
-	// consists of one operator. This is always a syntax error.
+	// Catch edge cases
 	match g {
 		Token::PreOperator(l, _) => {
 			return Err((l, ParserError::Syntax));