diff --git a/Cargo.lock b/Cargo.lock
index a83ebb9..a8b3e18 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -22,7 +22,7 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "daisy"
-version = "0.1.5"
+version = "0.2.0"
 dependencies = [
  "cfg-if",
  "rug",
diff --git a/Cargo.toml b/Cargo.toml
index 6652ee1..7db077f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "daisy"
-version = "0.1.5"
+version = "0.2.0"
 edition = "2021"
 
 [profile.release]
diff --git a/src/entry/unix/unix.rs b/src/entry/unix/unix.rs
index f431ad3..1cce689 100644
--- a/src/entry/unix/unix.rs
+++ b/src/entry/unix/unix.rs
@@ -13,9 +13,11 @@ use termion::{
 };
 
 use super::promptbuffer::PromptBuffer;
-use crate::tokens::EvalError;
+//use crate::tokens::EvalError;
 use crate::parser;
 use crate::command;
+use crate::evaluate::evaluate;
+use crate::evaluate::EvalError;
 
 
 
@@ -37,7 +39,7 @@ fn do_expression(
 			color::Fg(color::Red),
 			" ".repeat(l.pos + 4),
 			"^".repeat(l.len),
-			e.to_message(),
+			e.to_string(),
 			color::Fg(color::Reset),
 		)?;
 		return Ok(());
@@ -54,10 +56,11 @@ fn do_expression(
 		g.to_string()
 	)?;
 
+
 	// Evaluate expression
 	#[cfg(debug_assertions)]
 	RawTerminal::suspend_raw_mode(&stdout)?;
-	let g = g.evaluate();
+	let g = evaluate(&g);
 	#[cfg(debug_assertions)]
 	RawTerminal::activate_raw_mode(&stdout)?;
 
@@ -118,6 +121,7 @@ fn do_expression(
 	}
 
 
+
 	return Ok(());
 }
 
diff --git a/src/evaluate/evaluate.rs b/src/evaluate/evaluate.rs
new file mode 100644
index 0000000..fe66ef7
--- /dev/null
+++ b/src/evaluate/evaluate.rs
@@ -0,0 +1,81 @@
+use crate::parser::Token;
+use crate::parser::Constant;
+use crate::quantity::Quantity;
+
+use super::operator::op_apply;
+use super::EvalError;
+
+pub fn evaluate(t: &Token) -> Result<Token, EvalError> {
+	let mut g = t.clone();
+	let mut coords: Vec<usize> = Vec::with_capacity(16);
+	coords.push(0);
+
+	'outer: loop {
+
+		let mut h = &mut g;
+		for t in coords.iter() {
+			let inner = h.get_args_mut();
+
+			if inner.is_none() || *t >= inner.as_ref().unwrap().len() {
+				coords.pop();
+
+
+				let p = Token::get_at_coords(&mut g, &coords);
+
+				let e: Token = match p {
+					Token::Quantity(_) => { p.clone() },
+					Token::Constant(c) => {
+						match c {
+							// Mathematical constants
+							// 100 digits of each.
+							Constant::Pi => { Token::Quantity(Quantity::new_float_from_string(
+								"3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067"
+							).unwrap())},
+
+							Constant::E => { Token::Quantity(Quantity::new_float_from_string(
+								"2.718281828459045235360287471352662497757247093699959574966967627724076630353547594571382178525166427"
+							).unwrap()) },
+
+							Constant::Phi => { Token::Quantity(Quantity::new_float_from_string(
+								"1.618033988749894848204586834365638117720309179805762862135448622705260462818902449707207204189391137"
+							).unwrap()) },
+						}
+					},
+					Token::Operator(o,v) => { op_apply(o, &v)? }
+				};
+
+				//let e = p.eval()?;
+				*p = e;
+
+				if coords.len() == 0 { break 'outer; }
+				let l = coords.pop().unwrap();
+				coords.push(l + 1);
+				continue 'outer;
+			}
+
+			h = &mut inner.unwrap()[*t];
+		}
+
+
+
+		match h {
+			Token::Operator(_,_) => {
+				coords.push(0);
+				continue 'outer;
+			},
+
+			Token::Constant(_) => {
+				coords.push(0);
+				continue 'outer;
+			},
+
+			Token::Quantity(_) => {
+				let l = coords.pop().unwrap();
+				coords.push(l + 1);
+				continue 'outer;
+			}
+		};
+	}
+
+	return Ok(g);
+}
\ No newline at end of file
diff --git a/src/evaluate/function.rs b/src/evaluate/function.rs
new file mode 100644
index 0000000..3212145
--- /dev/null
+++ b/src/evaluate/function.rs
@@ -0,0 +1,102 @@
+use std::collections::VecDeque;
+
+use crate::parser::Token;
+use crate::parser::Function;
+use crate::parser::Operator;
+use super::EvalError;
+use super::operator::op_apply;
+use crate::quantity::Quantity;
+
+fn eval(t: Token) -> Result<Token, EvalError> {
+	Ok(match t {
+		Token::Quantity(_) => { t },
+		Token::Constant(_) => { Token::Quantity( Quantity::new_rational_from_string("1").unwrap() ) },
+		Token::Operator(mut o, v) => { op_apply(&mut o, &v)? }
+	})
+}
+
+pub fn func_apply(f: &Function, args: &VecDeque<Token>) -> Result<Token, EvalError> {
+	if args.len() != 1 {panic!()};
+	let a = &args[0];
+	let Token::Quantity(q) = a else {panic!()};
+
+	if !q.unitless() {
+		return Err(EvalError::IncompatibleUnit);
+	}
+
+	match f {
+		Function::Abs => { return Ok(Token::Quantity(q.abs())); },
+		Function::Floor => { return Ok(Token::Quantity(q.floor())); },
+		Function::Ceil => { return Ok(Token::Quantity(q.ceil())); },
+		Function::Round => { return Ok(Token::Quantity(q.round())); },
+
+		Function::NaturalLog => { return Ok(Token::Quantity(q.ln())); },
+		Function::TenLog => { return Ok(Token::Quantity(q.log10())); },
+
+		Function::Sin => { return Ok(Token::Quantity(q.sin())); },
+		Function::Cos => { return Ok(Token::Quantity(q.cos())); },
+		Function::Tan => { return Ok(Token::Quantity(q.tan())); },
+		Function::Asin => { return Ok(Token::Quantity(q.asin())); },
+		Function::Acos => { return Ok(Token::Quantity(q.acos())); },
+		Function::Atan => { return Ok(Token::Quantity(q.atan())); },
+
+		Function::Csc => {
+			return Ok(
+				eval(Token::Operator(
+					Operator::Flip,
+					VecDeque::from(vec!(Token::Quantity(q.sin())))
+				))?
+			);
+		},
+		Function::Sec => {
+			return Ok(
+				eval(Token::Operator(
+					Operator::Flip,
+					VecDeque::from(vec!(Token::Quantity(q.cos())))
+				))?
+			);
+		},
+		Function::Cot => {
+			return Ok(
+				eval(Token::Operator(
+					Operator::Flip,
+					VecDeque::from(vec!(Token::Quantity(q.tan())))
+				))?
+			);
+		},
+
+
+		Function::Sinh => { return Ok(Token::Quantity(q.sinh())); },
+		Function::Cosh => { return Ok(Token::Quantity(q.cosh())); },
+		Function::Tanh => { return Ok(Token::Quantity(q.tanh())); },
+		Function::Asinh => { return Ok(Token::Quantity(q.asinh())); },
+		Function::Acosh => { return Ok(Token::Quantity(q.acosh())); },
+		Function::Atanh => { return Ok(Token::Quantity(q.atanh())); },
+
+		Function::Csch => {
+			return Ok(
+				eval(Token::Operator(
+					Operator::Flip,
+					VecDeque::from(vec!(Token::Quantity(q.sinh())))
+				))?
+			);
+		},
+		Function::Sech => {
+			return Ok(
+				eval(Token::Operator(
+					Operator::Flip,
+					VecDeque::from(vec!(Token::Quantity(q.cosh())))
+				))?
+			);
+		},
+		Function::Coth => {
+			return Ok(
+				eval(Token::Operator(
+					Operator::Flip,
+					VecDeque::from(vec!(Token::Quantity(q.tanh())))
+				))?
+			);
+		},
+
+	}
+}
\ No newline at end of file
diff --git a/src/evaluate/mod.rs b/src/evaluate/mod.rs
new file mode 100644
index 0000000..5408ff2
--- /dev/null
+++ b/src/evaluate/mod.rs
@@ -0,0 +1,11 @@
+mod operator;
+mod function;
+mod evaluate;
+pub use self::evaluate::evaluate;
+
+pub enum EvalError {
+	BadMath,
+	TooBig,
+	ZeroDivision,
+	IncompatibleUnit
+}
\ No newline at end of file
diff --git a/src/evaluate/operator.rs b/src/evaluate/operator.rs
new file mode 100644
index 0000000..dd6c7bf
--- /dev/null
+++ b/src/evaluate/operator.rs
@@ -0,0 +1,165 @@
+use std::collections::VecDeque;
+
+use crate::quantity::Quantity;
+use crate::parser::Operator;
+use crate::parser::Token;
+use super::EvalError;
+use super::function::func_apply;
+
+
+pub fn op_apply(op: &mut Operator, args: &VecDeque<Token>) -> Result<Token, EvalError> {
+	match op {
+		Operator::ImplicitMultiply |
+		Operator::Sqrt |
+		Operator::Divide |
+		Operator::Subtract => { panic!() }
+
+		Operator::Negative => {
+			if args.len() != 1 {panic!()};
+			let args = &args[0];
+
+			if let Token::Quantity(v) = args {
+				return Ok(Token::Quantity(-v.clone()));
+			} else { panic!(); }
+		},
+
+		Operator::Flip => {
+			if args.len() != 1 {panic!()};
+			let args = &args[0];
+
+			if let Token::Quantity(v) = args {
+				if v.is_zero() { return Err(EvalError::ZeroDivision); }
+				return Ok(Token::Quantity(
+					Quantity::new_rational(1f64).unwrap()/v.clone()
+				));
+			} else { panic!(); }
+		},
+
+		Operator::Add => {
+			let mut sum: Quantity;
+			if let Token::Quantity(s) = &args[0] {
+				sum = s.clone();
+			} else {panic!()};
+
+			let mut i: usize = 1;
+			while i < args.len() {
+				let j = &args[i];
+				if let Token::Quantity(v) = j {
+
+					if !sum.unit.compatible_with(&v.unit) {
+						return Err(EvalError::IncompatibleUnit);
+					}
+
+					sum += v.clone();
+				} else {
+					panic!();
+				}
+				i += 1;
+			}
+			return Ok(Token::Quantity(sum));
+		},
+
+		Operator::Multiply => {
+			let mut prod = Quantity::new_rational(1f64).unwrap();
+			for i in args.iter() {
+				let j = i;
+				if let Token::Quantity(v) = j {
+					prod *= v.clone();
+				} else {
+					panic!();
+				}
+			}
+			return Ok(Token::Quantity(prod));
+		},
+
+		Operator::ModuloLong
+		| Operator::Modulo => {
+			if args.len() != 2 {panic!()};
+			let a = &args[0];
+			let b = &args[1];
+
+			if let Token::Quantity(va) = a {
+				if let Token::Quantity(vb) = b {
+
+					if !(va.unitless() && vb.unitless()) {
+						return Err(EvalError::IncompatibleUnit);
+					}
+
+					if vb <= &Quantity::new_rational(1f64).unwrap() { return Err(EvalError::BadMath); }
+					if va.fract() != Quantity::new_rational(0f64).unwrap() { return Err(EvalError::BadMath); }
+					if vb.fract() != Quantity::new_rational(0f64).unwrap() { return Err(EvalError::BadMath); }
+
+					return Ok(Token::Quantity(va.clone() % vb.clone()));
+				} else { panic!(); }
+			} else { panic!(); }
+		},
+
+		Operator::UnitConvert
+		=> {
+			if args.len() != 2 {panic!()};
+			let a = &args[0];
+			let b = &args[1];
+
+			if let Token::Quantity(va) = a {
+				if let Token::Quantity(vb) = b {
+					let n = va.clone().convert_to(vb.clone());
+					if n.is_none() {
+						return Err(EvalError::IncompatibleUnit);
+					}
+					return Ok(Token::Quantity(n.unwrap()));
+				} else { panic!(); }
+			} else { panic!(); }
+		},
+
+		Operator::Power => {
+			if args.len() != 2 {panic!()};
+			let a = &args[0];
+			let b = &args[1];
+
+			if let Token::Quantity(va) = a {
+				if let Token::Quantity(vb) = b {
+
+					if !vb.unitless() {
+						return Err(EvalError::IncompatibleUnit);
+					}
+
+					if va.is_zero() && vb.is_negative() {
+						return Err(EvalError::ZeroDivision);
+					}
+
+					let p = va.pow(vb.clone());
+					if p.is_nan() {return Err(EvalError::BadMath);}
+					return Ok(Token::Quantity(p));
+				} else { panic!(); }
+			} else { panic!(); }
+		},
+
+		Operator::Factorial => {
+			if args.len() != 1 {panic!()};
+			let args = &args[0];
+
+			if let Token::Quantity(v) = args {
+
+				if !v.unitless() {
+					return Err(EvalError::IncompatibleUnit);
+				}
+
+				if !v.fract().is_zero() { return Err(EvalError::BadMath); }
+				if v > &Quantity::new_rational(50_000f64).unwrap() { return Err(EvalError::TooBig); }
+
+				let mut prod = Quantity::new_rational(1f64).unwrap();
+				let mut u = v.clone();
+				while u > Quantity::new_rational(0f64).unwrap() {
+					prod *= u.clone();
+					u = u - Quantity::new_rational(1f64).unwrap();
+				}
+
+				return Ok(Token::Quantity(prod));
+			} else { panic!(); }
+		},
+
+		Operator::Function(f) => {
+			return func_apply(f, args);
+		}
+	};
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 56b8cde..bac372b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,8 @@
-pub mod tokens;
 pub mod parser;
 pub mod command;
 pub mod quantity;
+pub mod evaluate;
 
-//use crate::tokens::Token;
-//use crate::parser::ParserError;
-//use crate::parser::LineLocation;
 
 mod entry;
 use crate::entry::main_e;
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index c6ebe59..cb7ea5e 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -1,174 +1,21 @@
-use std::collections::VecDeque;
+mod stage;
 
+mod pretoken;
+mod parsererror;
+mod token;
 
-mod tokenize;
-mod treeify;
-mod groupify;
-mod find_subs;
-
-
-use crate::parser::tokenize::tokenize;
-use crate::parser::groupify::groupify;
-use crate::parser::treeify::treeify;
-use crate::parser::find_subs::find_subs;
-
-use crate::quantity::Quantity;
-use crate::quantity::Unit;
-
-use crate::tokens::Token;
-
-/// Specifies the location of a token in an input string.
-/// Used to locate ParserErrors.
-#[derive(Debug)]
-#[derive(Copy, Clone)]
-pub struct LineLocation {
-	pub pos: usize,
-	pub len: usize
-}
-
-#[derive(Debug)]
-enum PreToken {
-	PreNumber(LineLocation, String),
-	PreWord(LineLocation, String),
-	PreOperator(LineLocation, String),
-
-	PreGroupStart(LineLocation),
-	PreGroupEnd(LineLocation),
-	PreGroup(LineLocation, VecDeque<PreToken>),
-
-	Container(Token)
-}
-
-impl PreToken {
-	#[inline(always)]
-	pub fn get_line_location(&self) -> &LineLocation {
-		match self {
-			PreToken::PreNumber(l, _)
-			| PreToken::PreWord(l, _)
-			| PreToken::PreOperator(l, _)
-			| PreToken::PreGroupStart(l)
-			| PreToken::PreGroupEnd(l)
-			| PreToken::PreGroup(l, _)
-			=> l,
-
-			_ => panic!()
-		}
-	}
-
-	#[inline(always)]
-	pub fn get_mut_line_location(&mut self) -> &mut LineLocation {
-		match self {
-			PreToken::PreNumber(l, _)
-			| PreToken::PreWord(l, _)
-			| PreToken::PreOperator(l, _)
-			| PreToken::PreGroupStart(l)
-			| PreToken::PreGroupEnd(l)
-			| PreToken::PreGroup(l, _)
-			=> l,
-
-			_ => panic!()
-		}
-	}
-
-	#[inline(always)]
-	pub fn to_token(self) -> Result<Token, (LineLocation, ParserError)>{
-		match self {
-			PreToken::PreNumber(l, mut s) => {
-
-				// The length check here ensures that
-				// `.` is not parsed as `0.`
-				// That should be a syntax error.
-				if s.len() != 1 && &s[0..1] == "." {
-					s.insert(0, '0');
-				}
-
-				let r = Quantity::new_rational_from_string(&s);
-				if r.is_none() {
-					return Err((l, ParserError::BadNumber))
-				}
-				return Ok(Token::Number(r.unwrap()));
-			},
-
-			PreToken::PreWord(l, s) => {
-				let c = match &s[..] {
-					// Mathematical constants
-					// 100 digits of each.
-					"π"|"pi" => { Some((Quantity::new_float_from_string(
-						"3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067"
-					).unwrap(), String::from("π")))},
-
-					"e" => { Some((Quantity::new_float_from_string(
-						"2.718281828459045235360287471352662497757247093699959574966967627724076630353547594571382178525166427"
-					).unwrap(), String::from("e"))) },
-
-					"phi"|"φ" => { Some((Quantity::new_float_from_string(
-						"1.618033988749894848204586834365638117720309179805762862135448622705260462818902449707207204189391137"
-					).unwrap(), String::from("φ"))) },
-
-					_ => { None }
-				};
-
-				if c.is_some() {
-					let (a, b) = c.unwrap();
-					return Ok(Token::Constant(a, b));
-				}
-
-				let c = Unit::from_string(&s);
-				if c.is_some() { return Ok(Token::Number(c.unwrap())); }
-
-				return Err((l, ParserError::Undefined(s)));
-			}
-
-			PreToken::Container(v) => { return Ok(v); }
-
-			PreToken::PreOperator(_,_)
-			| PreToken::PreGroupStart(_)
-			| PreToken::PreGroupEnd(_)
-			| PreToken::PreGroup(_, _)
-			=> panic!()
-		};
-	}
-
-}
-
-
-/// Types of parser errors.
-/// If we cannot parse a string, one of these is returned.
-#[derive(Debug)]
-pub enum ParserError {
-	//MissingCloseParen,
-	ExtraCloseParen,
-	EmptyGroup,
-	Syntax,
-	Undefined(String),
-	BadNumber
-}
-
-impl ParserError {
-	pub fn to_message(&self) -> String {
-		match self {
-			//ParserError::MissingCloseParen => {
-			//	String::from("This group is never closed")
-			//},
-			ParserError::ExtraCloseParen => {
-				String::from("Extra close parenthesis")
-			},
-			ParserError::EmptyGroup => {
-				String::from("Groups can't be empty")
-			},
-			ParserError::Syntax => {
-				String::from("Syntax")
-			},
-			ParserError::Undefined(s) => {
-				format!("\"{s}\" isn't defined")
-			},
-			ParserError::BadNumber => {
-				String::from("Invalid number")
-			}
-		}
-	}
-}
+use self::{
+	pretoken::PreToken,
+	parsererror::ParserError,
+	parsererror::LineLocation
+};
 
+pub use self::{
+	token::Token,
+	token::Constant,
+	token::Operator,
+	token::Function,
+};
 
 
 pub fn parse(
@@ -178,10 +25,10 @@ pub fn parse(
 	(LineLocation, ParserError)
 > {
 
-	let tokens = tokenize(s);
-	let (_, tokens) = find_subs(tokens);
-	let g = groupify(tokens)?;
-	let g = treeify(g)?;
+	let tokens = stage::tokenize(s);
+	let (_, tokens) = stage::find_subs(tokens);
+	let g = stage::groupify(tokens)?;
+	let g = stage::treeify(g)?;
 
 	return Ok(g);
 }
@@ -198,8 +45,8 @@ pub fn substitute(
 	let mut new_s = s.clone();
 
 	let l = s.chars().count();
-	let tokens = tokenize(s);
-	let (subs, _) = find_subs(tokens);
+	let tokens = stage::tokenize(s);
+	let (subs, _) = stage::find_subs(tokens);
 	let mut new_c = l - c;
 
 	for r in subs.iter() {
diff --git a/src/parser/parsererror.rs b/src/parser/parsererror.rs
new file mode 100644
index 0000000..b6c6701
--- /dev/null
+++ b/src/parser/parsererror.rs
@@ -0,0 +1,45 @@
+/// Specifies the location of a token in an input string.
+/// Used to locate ParserErrors.
+#[derive(Debug)]
+#[derive(Copy, Clone)]
+pub struct LineLocation {
+	pub pos: usize,
+	pub len: usize
+}
+
+/// Types of parser errors.
+/// If we cannot parse a string, one of these is returned.
+#[derive(Debug)]
+pub enum ParserError {
+	//MissingCloseParen,
+	ExtraCloseParen,
+	EmptyGroup,
+	Syntax,
+	Undefined(String),
+	BadNumber
+}
+
+impl ToString for ParserError {
+	fn to_string(&self) -> String {
+		match self {
+			//ParserError::MissingCloseParen => {
+			//	String::from("This group is never closed")
+			//},
+			ParserError::ExtraCloseParen => {
+				String::from("Extra close parenthesis")
+			},
+			ParserError::EmptyGroup => {
+				String::from("Groups can't be empty")
+			},
+			ParserError::Syntax => {
+				String::from("Syntax")
+			},
+			ParserError::Undefined(s) => {
+				format!("\"{s}\" isn't defined")
+			},
+			ParserError::BadNumber => {
+				String::from("Invalid number")
+			}
+		}
+	}
+}
diff --git a/src/parser/pretoken.rs b/src/parser/pretoken.rs
new file mode 100644
index 0000000..4d3e337
--- /dev/null
+++ b/src/parser/pretoken.rs
@@ -0,0 +1,104 @@
+use std::collections::VecDeque;
+use crate::quantity::Unit;
+use crate::quantity::Quantity;
+
+use super::{
+	LineLocation,
+	ParserError,
+	Token,
+	Constant
+};
+
+
+#[derive(Debug)]
+pub enum PreToken {
+	PreQuantity(LineLocation, String),
+	PreWord(LineLocation, String),
+	PreOperator(LineLocation, String),
+
+	PreGroupStart(LineLocation),
+	PreGroupEnd(LineLocation),
+	PreGroup(LineLocation, VecDeque<PreToken>),
+
+	Container(Token)
+}
+
+impl PreToken {
+	#[inline(always)]
+	pub fn get_line_location(&self) -> &LineLocation {
+		match self {
+			PreToken::PreQuantity(l, _)
+			| PreToken::PreWord(l, _)
+			| PreToken::PreOperator(l, _)
+			| PreToken::PreGroupStart(l)
+			| PreToken::PreGroupEnd(l)
+			| PreToken::PreGroup(l, _)
+			=> l,
+
+			_ => panic!()
+		}
+	}
+
+	#[inline(always)]
+	pub fn get_mut_line_location(&mut self) -> &mut LineLocation {
+		match self {
+			PreToken::PreQuantity(l, _)
+			| PreToken::PreWord(l, _)
+			| PreToken::PreOperator(l, _)
+			| PreToken::PreGroupStart(l)
+			| PreToken::PreGroupEnd(l)
+			| PreToken::PreGroup(l, _)
+			=> l,
+
+			_ => panic!()
+		}
+	}
+
+	#[inline(always)]
+	pub fn to_token(self) -> Result<Token, (LineLocation, ParserError)>{
+		match self {
+			PreToken::PreQuantity(l, mut s) => {
+
+				// The length check here ensures that
+				// `.` is not parsed as `0.`
+				// That should be a syntax error.
+				if s.len() != 1 && &s[0..1] == "." {
+					s.insert(0, '0');
+				}
+
+				let r = Quantity::new_rational_from_string(&s);
+				if r.is_none() {
+					return Err((l, ParserError::BadNumber))
+				}
+				return Ok(Token::Quantity(r.unwrap()));
+			},
+
+			PreToken::PreWord(l, s) => {
+				let c = match &s[..] {
+					"π"|"pi" => { Some(Constant::Pi)},
+					"e" => { Some(Constant::E) },
+					"phi"|"φ" => { Some(Constant::Phi) },
+					_ => { None }
+				};
+
+				if c.is_some() {
+					return Ok(Token::Constant(c.unwrap()));
+				}
+
+				let c = Unit::from_string(&s);
+				if c.is_some() { return Ok(Token::Quantity(c.unwrap())); }
+
+				return Err((l, ParserError::Undefined(s)));
+			}
+
+			PreToken::Container(v) => { return Ok(v); }
+
+			PreToken::PreOperator(_,_)
+			| PreToken::PreGroupStart(_)
+			| PreToken::PreGroupEnd(_)
+			| PreToken::PreGroup(_, _)
+			=> panic!()
+		};
+	}
+
+}
\ No newline at end of file
diff --git a/src/parser/find_subs.rs b/src/parser/stage/find_subs.rs
similarity index 96%
rename from src/parser/find_subs.rs
rename to src/parser/stage/find_subs.rs
index 88842ee..e9966f7 100644
--- a/src/parser/find_subs.rs
+++ b/src/parser/stage/find_subs.rs
@@ -1,10 +1,12 @@
 use std::collections::VecDeque;
 
-use crate::parser::PreToken;
-use crate::parser::LineLocation;
+use super::super::{
+	PreToken,
+	LineLocation
+};
 
 
-pub(in crate::parser) fn find_subs(
+pub fn find_subs(
 	mut g: VecDeque<PreToken>,
 ) -> (
 	Vec<(LineLocation, String)>,
diff --git a/src/parser/groupify.rs b/src/parser/stage/groupify.rs
similarity index 90%
rename from src/parser/groupify.rs
rename to src/parser/stage/groupify.rs
index 75bb337..a2811f2 100644
--- a/src/parser/groupify.rs
+++ b/src/parser/stage/groupify.rs
@@ -1,10 +1,11 @@
 use std::collections::VecDeque;
 
-use crate::parser::PreToken;
-use crate::parser::LineLocation;
-use crate::parser::ParserError;
-
-use crate::tokens::Operator;
+use super::super::{
+	PreToken,
+	LineLocation,
+	ParserError,
+	Operator
+};
 
 
 fn lookback_signs(
@@ -99,7 +100,6 @@ fn lookback(
 
 	lookback_signs(g)?;
 
-
 	let mut i: usize = 0;
 	while i < g.len() {
 		if i >= 1 {
@@ -109,12 +109,12 @@ fn lookback(
 			match (&a, &b) {
 				// Insert ImplicitMultiply
 				(PreToken::PreGroup(_,_), PreToken::PreGroup(l ,_))
-				| (PreToken::PreGroup(_,_), PreToken::PreNumber(l,_))
-				| (PreToken::PreNumber(_,_), PreToken::PreGroup(l,_))
+				| (PreToken::PreGroup(_,_), PreToken::PreQuantity(l,_))
+				| (PreToken::PreQuantity(_,_), PreToken::PreGroup(l,_))
 				| (PreToken::PreGroup(_,_), PreToken::PreWord(l,_))
 				| (PreToken::PreWord(_,_), PreToken::PreGroup(l,_))
-				| (PreToken::PreNumber(_,_), PreToken::PreWord(l,_))
-				| (PreToken::PreWord(_,_), PreToken::PreNumber(l,_))
+				| (PreToken::PreQuantity(_,_), PreToken::PreWord(l,_))
+				| (PreToken::PreWord(_,_), PreToken::PreQuantity(l,_))
 				| (PreToken::PreWord(_,_), PreToken::PreWord(l,_))
 				=> {
 					let loc = LineLocation{pos: l.pos-1, len: 0};
@@ -128,7 +128,7 @@ fn lookback(
 				},
 
 				// Insert implicit multiplications for right-unary operators
-				(PreToken::PreNumber(_,_), PreToken::PreOperator(l,s))
+				(PreToken::PreQuantity(_,_), PreToken::PreOperator(l,s))
 				| (PreToken::PreGroup(_,_), PreToken::PreOperator(l,s))
 				| (PreToken::PreWord(_,_), PreToken::PreOperator(l,s))
 				=> {
@@ -149,7 +149,7 @@ fn lookback(
 				},
 
 				// Insert implicit multiplications for left-unary operators.
-				(PreToken::PreOperator(_,s), PreToken::PreNumber(l,_))
+				(PreToken::PreOperator(_,s), PreToken::PreQuantity(l,_))
 				| (PreToken::PreOperator(_,s), PreToken::PreGroup(l,_))
 				| (PreToken::PreOperator(_,s), PreToken::PreWord(l,_))
 				=> {
@@ -170,7 +170,7 @@ fn lookback(
 				},
 
 				// The following are syntax errors
-				(PreToken::PreNumber(la,_), PreToken::PreNumber(lb,_))
+				(PreToken::PreQuantity(la,_), PreToken::PreQuantity(lb,_))
 				=> {
 					return Err((
 						LineLocation{pos: la.pos, len: lb.pos - la.pos + lb.len},
@@ -188,7 +188,7 @@ fn lookback(
 }
 
 
-pub(in crate::parser) fn groupify(
+pub fn groupify(
 	mut g: VecDeque<PreToken>
 ) -> Result<
 	PreToken,
diff --git a/src/parser/stage/mod.rs b/src/parser/stage/mod.rs
new file mode 100644
index 0000000..f7a9df3
--- /dev/null
+++ b/src/parser/stage/mod.rs
@@ -0,0 +1,11 @@
+mod tokenize;
+mod find_subs;
+mod groupify;
+mod treeify;
+
+pub (in super) use self::{
+	tokenize::tokenize,
+	find_subs::find_subs,
+	groupify::groupify,
+	treeify::treeify,
+};
\ No newline at end of file
diff --git a/src/parser/tokenize.rs b/src/parser/stage/tokenize.rs
similarity index 88%
rename from src/parser/tokenize.rs
rename to src/parser/stage/tokenize.rs
index 7792ad3..98390d0 100644
--- a/src/parser/tokenize.rs
+++ b/src/parser/stage/tokenize.rs
@@ -1,9 +1,10 @@
 use std::collections::VecDeque;
 
-use crate::parser::PreToken;
-use crate::parser::LineLocation;
-
-use crate::tokens::Operator;
+use super::super::{
+	PreToken,
+	LineLocation,
+	Operator
+};
 
 // Called whenever a token is finished.
 #[inline(always)]
@@ -16,7 +17,7 @@ fn push_token(g: &mut VecDeque<PreToken>, t: Option<PreToken>, stop_i: usize) {
 		PreToken::PreGroupStart(ref mut l)
 		| PreToken::PreGroupEnd(ref mut l)
 		| PreToken::PreOperator(ref mut l, _)
-		| PreToken::PreNumber(ref mut l, _)
+		| PreToken::PreQuantity(ref mut l, _)
 		| PreToken::PreWord(ref mut l, _)
 		=> {
 			*l = LineLocation{
@@ -33,10 +34,10 @@ fn push_token(g: &mut VecDeque<PreToken>, t: Option<PreToken>, stop_i: usize) {
 
 	// `2e` isn't exponential notation, it's 2*e.
 	// If a number ends in `e`, disconnect the `e` and make it a word.
-	if let PreToken::PreNumber(l, s) = &t {
+	if let PreToken::PreQuantity(l, s) = &t {
 		let last = &s[s.len()-1..];
 		if last == "e" {
-			g.push_back(PreToken::PreNumber(
+			g.push_back(PreToken::PreQuantity(
 				LineLocation { pos: l.pos, len: l.len-1 },
 				String::from(&s[0..s.len()-1])
 			));
@@ -60,7 +61,7 @@ fn push_token(g: &mut VecDeque<PreToken>, t: Option<PreToken>, stop_i: usize) {
 }
 
 /// Turns a string into Tokens. First stage of parsing.
-pub(in crate::parser) fn tokenize(input: &String) -> VecDeque<PreToken> {
+pub fn tokenize(input: &String) -> VecDeque<PreToken> {
 	let mut t: Option<PreToken> = None; // The current token we're reading
 	let mut g: VecDeque<PreToken> = VecDeque::with_capacity(32);
 
@@ -73,7 +74,7 @@ pub(in crate::parser) fn tokenize(input: &String) -> VecDeque<PreToken> {
 				match &mut t {
 					// If we're already building a number,
 					// append.
-					Some(PreToken::PreNumber(_, val)) => {
+					Some(PreToken::PreQuantity(_, val)) => {
 						val.push(if c == ',' {'.'} else {c});
 					},
 
@@ -81,7 +82,7 @@ pub(in crate::parser) fn tokenize(input: &String) -> VecDeque<PreToken> {
 					// previous token and start one.
 					_ => {
 						push_token(&mut g, t, i);
-						t = Some(PreToken::PreNumber(LineLocation{pos: i, len: 0}, String::from(c)));
+						t = Some(PreToken::PreQuantity(LineLocation{pos: i, len: 0}, String::from(c)));
 					}
 				};
 			},
@@ -91,7 +92,7 @@ pub(in crate::parser) fn tokenize(input: &String) -> VecDeque<PreToken> {
 			'e' => {
 				match &mut t {
 					Some(PreToken::PreWord(_, val)) => { val.push(c); },
-					Some(PreToken::PreNumber(_, val)) => { val.push(c); },
+					Some(PreToken::PreQuantity(_, val)) => { val.push(c); },
 
 					_ => {
 						push_token(&mut g, t, i);
@@ -105,7 +106,7 @@ pub(in crate::parser) fn tokenize(input: &String) -> VecDeque<PreToken> {
 			// or it can specify a negative exponent.
 			'-' | '+' => {
 				match &mut t {
-					Some(PreToken::PreNumber(_, val)) => {
+					Some(PreToken::PreQuantity(_, val)) => {
 						if &val[val.len()-1..] == "e" {
 							// If the current number ends in an `e`,
 							// this negative specifies a negative exponent
diff --git a/src/parser/treeify.rs b/src/parser/stage/treeify.rs
similarity index 97%
rename from src/parser/treeify.rs
rename to src/parser/stage/treeify.rs
index cae4c90..ca9559b 100644
--- a/src/parser/treeify.rs
+++ b/src/parser/stage/treeify.rs
@@ -1,11 +1,12 @@
 use std::collections::VecDeque;
 
-use crate::parser::PreToken;
-use crate::parser::ParserError;
-use crate::parser::LineLocation;
-
-use crate::tokens::Token;
-use crate::tokens::Operator;
+use super::super::{
+	PreToken,
+	ParserError,
+	LineLocation,
+	Token,
+	Operator
+};
 
 fn treeify_binary(
 	i: usize,
@@ -269,7 +270,7 @@ fn treeify_unary(
 }
 
 
-pub(in crate::parser) fn treeify(
+pub fn treeify(
 	mut g: PreToken,
 ) -> Result<Token, (LineLocation, ParserError)> {
 
diff --git a/src/parser/token/constant.rs b/src/parser/token/constant.rs
new file mode 100644
index 0000000..15a1ae7
--- /dev/null
+++ b/src/parser/token/constant.rs
@@ -0,0 +1,17 @@
+#[derive(Debug)]
+#[derive(Clone)]
+pub enum Constant {
+	Pi,
+	Phi,
+	E
+}
+
+impl Constant {
+	pub fn to_string(&self) -> String {
+		match self {
+			Constant::Pi => { String::from("π") },
+			Constant::Phi => { String::from("φ") },
+			Constant::E => { String::from("e") },
+		}
+	}
+}
\ No newline at end of file
diff --git a/src/parser/token/function.rs b/src/parser/token/function.rs
new file mode 100644
index 0000000..bf3f7d1
--- /dev/null
+++ b/src/parser/token/function.rs
@@ -0,0 +1,62 @@
+#[derive(Debug)]
+#[derive(Copy, Clone)]
+pub enum Function {
+	Abs,
+	Floor,
+	Ceil,
+	Round,
+
+	NaturalLog,
+	TenLog,
+
+	Sin,
+	Cos,
+	Tan,
+	Asin,
+	Acos,
+	Atan,
+	Csc,
+	Sec,
+	Cot,
+
+	Sinh,
+	Cosh,
+	Tanh,
+	Asinh,
+	Acosh,
+	Atanh,
+	Csch,
+	Sech,
+	Coth,
+}
+
+impl Function {
+	pub fn to_string(&self) -> String {
+		match self {
+			Function::Abs => { String::from("abs") },
+			Function::Floor => { String::from("floor") },
+			Function::Ceil => { String::from("ceil") },
+			Function::Round => { String::from("round") },
+			Function::NaturalLog => { String::from("ln") },
+			Function::TenLog => { String::from("log") },
+			Function::Sin => { String::from("sin") },
+			Function::Cos => { String::from("cos") },
+			Function::Tan => { String::from("tan") },
+			Function::Asin => { String::from("asin") },
+			Function::Acos => { String::from("acos") },
+			Function::Atan => { String::from("atan") },
+			Function::Csc => { String::from("csc") },
+			Function::Sec => { String::from("sec") },
+			Function::Cot => { String::from("cot") },
+			Function::Sinh => { String::from("sinh") },
+			Function::Cosh => { String::from("cosh") },
+			Function::Tanh => { String::from("tanh") },
+			Function::Asinh => { String::from("asinh") },
+			Function::Acosh => { String::from("acosh") },
+			Function::Atanh => { String::from("atanh") },
+			Function::Csch => { String::from("csch") },
+			Function::Sech => { String::from("sech") },
+			Function::Coth => { String::from("coth") },
+		}
+	}
+}
\ No newline at end of file
diff --git a/src/parser/token/mod.rs b/src/parser/token/mod.rs
new file mode 100644
index 0000000..564b412
--- /dev/null
+++ b/src/parser/token/mod.rs
@@ -0,0 +1,9 @@
+mod operator;
+mod function;
+mod token;
+mod constant;
+
+pub use self::operator::Operator;
+pub use self::function::Function;
+pub use self::token::Token;
+pub use self::constant::Constant;
\ No newline at end of file
diff --git a/src/tokens/operator.rs b/src/parser/token/operator.rs
similarity index 55%
rename from src/tokens/operator.rs
rename to src/parser/token/operator.rs
index 1473161..c327e00 100644
--- a/src/tokens/operator.rs
+++ b/src/parser/token/operator.rs
@@ -1,11 +1,10 @@
-use std::collections::VecDeque;
 use std::cmp::Ordering;
-
-use crate::tokens::Token;
-use crate::tokens::Function;
-use crate::tokens::EvalError;
+use std::collections::VecDeque;
 use crate::quantity::Quantity;
 
+use super::Token;
+use super::Function;
+
 
 /// Operator types, in order of increasing priority.
 #[derive(Debug)]
@@ -54,159 +53,9 @@ impl PartialOrd for Operator {
 }
 
 impl Operator {
-
 	#[inline(always)]
-	fn add_parens_to_arg(&self, arg: &Token) -> String {
-		let mut astr: String = arg.to_string();
-		if let Token::Operator(o,_) = arg {
-			if o < self {
-				astr = format!("({})", astr);
-			}
-		}
-		return astr;
-	}
-
-	#[inline(always)]
-	fn add_parens_to_arg_strict(&self, arg: &Token) -> String {
-		let mut astr: String = arg.to_string();
-		if let Token::Operator(o,_) = arg {
-			if o <= self {
-				astr = format!("({})", astr);
-			}
-		}
-		return astr;
-	}
-
-	pub fn print(&self, args: &VecDeque<Token>) -> String {
-		match self {
-			Operator::ImplicitMultiply |
-			Operator::Sqrt |
-			Operator::Divide |
-			Operator::Subtract => { panic!() }
-
-			Operator::Flip => {
-				return format!("1/{}", Operator::Divide.add_parens_to_arg(&args[0]));
-			},
-
-			Operator::Negative => {
-				return format!("-{}", self.add_parens_to_arg(&args[0]));
-			},
-
-			Operator::ModuloLong => {
-				return format!(
-					"{} mod {}",
-					self.add_parens_to_arg(&args[0]),
-					self.add_parens_to_arg(&args[1])
-				);
-			},
-
-			Operator::UnitConvert => {
-				return format!(
-					"{} to {}",
-					self.add_parens_to_arg(&args[0]),
-					self.add_parens_to_arg(&args[1])
-				);
-			},
-
-			Operator::Modulo => {
-				return format!(
-					"{} % {}",
-					self.add_parens_to_arg(&args[0]),
-					self.add_parens_to_arg(&args[1])
-				);
-			},
-
-			Operator::Power => {
-				return format!(
-					"{}^{}",
-					self.add_parens_to_arg_strict(&args[0]),
-					self.add_parens_to_arg_strict(&args[1])
-				);
-			},
-
-			Operator::Factorial => {
-				return format!("{}!", self.add_parens_to_arg(&args[0]));
-			},
-
-
-
-			Operator::Add => {
-				let a = &args[0];
-				let mut b = &args[1];
-				let mut sub = false;
-
-				let tmp;
-
-				if let Token::Operator(o,ar) = b {
-					if let Operator::Negative = o {
-						sub = true;
-						b = &ar[0];
-					}
-				} else if let Token::Number(q) = b {
-					if q.is_negative() {
-						sub = true;
-						tmp = Token::Number(-q.clone());
-						b = &tmp;
-					}
-				}
-				let (b, sub) = (b, sub);
-
-				if sub {
-					return format!("{} - {}", self.add_parens_to_arg(a), self.add_parens_to_arg(b));
-				} else {
-					return format!("{} + {}", self.add_parens_to_arg(a), self.add_parens_to_arg(b));
-				}
-			},
-
-			Operator::Multiply => {
-				let a = &args[0];
-				let mut b = &args[1];
-				let mut div = false;
-
-				if let Token::Operator(o,ar) = b {
-					if let Operator::Flip = o {
-						div = true;
-						b = &ar[0];
-					}
-				}
-				let (b, div) = (b, div);
-
-				if div {
-					return format!("{} ÷ {}",
-						self.add_parens_to_arg_strict(a),
-						self.add_parens_to_arg_strict(b)
-					);
-				} else {
-
-					// Ommit times sign when we have a number
-					// multiplied by a unit (like 10 m)
-					// Times sign should stay in all other cases.
-					let no_times = if let Token::Number(p) = b {
-						if let Token::Number(q) = a {
-							(!p.unitless() && p.is_one()) &&
-							!(!q.unitless() && p.is_one())
-						} else {false}
-					} else {false};
-
-					if no_times {
-						return format!("{} {}",
-							self.add_parens_to_arg_strict(a),
-							self.add_parens_to_arg_strict(b)
-						);
-					} else {
-						return format!("{} × {}",
-							self.add_parens_to_arg_strict(a),
-							self.add_parens_to_arg_strict(b)
-						);
-					}
-
-				}
-			},
-
-			Operator::Function(s) => {
-				return format!("{}({})", s.to_string(), args[0].to_string());
-			}
-		};
+	pub fn as_int(&self) -> usize {
+		unsafe { *<*const _>::from(self).cast::<usize>() }
 	}
 
 	#[inline(always)]
@@ -276,12 +125,6 @@ impl Operator {
 		}
 	}
 
-	#[inline(always)]
-	pub fn as_int(&self) -> usize {
-		unsafe { *<*const _>::from(self).cast::<usize>() }
-	}
-
-
 	#[inline(always)]
 	pub fn into_token(self, mut args: VecDeque<Token>) -> Token {
 		match self {
@@ -291,8 +134,8 @@ impl Operator {
 				let b = args.pop_front().unwrap();
 
 				let b_new;
-				if let Token::Number(q) = b {
-					b_new = Token::Number(-q);
+				if let Token::Quantity(q) = b {
+					b_new = Token::Quantity(-q);
 				} else {
 					b_new = Token::Operator(Operator::Negative, VecDeque::from(vec!(b)));
 				}
@@ -321,7 +164,7 @@ impl Operator {
 
 				Token::Operator(
 					Operator::Power,
-					VecDeque::from(vec!(a, Token::Number(Quantity::new_rational(0.5).unwrap())))
+					VecDeque::from(vec!(a, Token::Quantity(Quantity::new_rational_from_string("0.5").unwrap())))
 				)
 			},
 
@@ -341,164 +184,137 @@ impl Operator {
 			=> { Token::Operator(self, args) },
 		}
 	}
-}
 
-impl Operator{
-	pub fn apply(&self, args: &VecDeque<Token>) -> Result<Token, EvalError> {
+
+	#[inline(always)]
+	fn add_parens_to_arg(&self, arg: &Token) -> String {
+		let mut astr: String = arg.to_string();
+		if let Token::Operator(o,_) = arg {
+			if o < self {
+				astr = format!("({})", astr);
+			}
+		}
+		return astr;
+	}
+
+	#[inline(always)]
+	fn add_parens_to_arg_strict(&self, arg: &Token) -> String {
+		let mut astr: String = arg.to_string();
+		if let Token::Operator(o,_) = arg {
+			if o <= self {
+				astr = format!("({})", astr);
+			}
+		}
+		return astr;
+	}
+
+
+	pub fn print(&self, args: &VecDeque<Token>) -> String {
 		match self {
 			Operator::ImplicitMultiply |
 			Operator::Sqrt |
 			Operator::Divide |
 			Operator::Subtract => { panic!() }
 
-			Operator::Negative => {
-				if args.len() != 1 {panic!()};
-				let args = args[0].as_number();
-
-				if let Token::Number(v) = args {
-					return Ok(Token::Number(-v));
-				} else { panic!(); }
-			},
-
 			Operator::Flip => {
-				if args.len() != 1 {panic!()};
-				let args = args[0].as_number();
-
-				if let Token::Number(v) = args {
-					if v.is_zero() { return Err(EvalError::ZeroDivision); }
-					return Ok(Token::Number(
-						Quantity::new_rational(1f64).unwrap()/v
-					));
-				} else { panic!(); }
+				return format!("{}⁻¹", Operator::Divide.add_parens_to_arg(&args[0]));
 			},
 
-			Operator::Add => {
-				let mut sum;
-				if let Token::Number(s) = args[0].as_number() {
-					sum = s;
-				} else {panic!()};
-
-				let mut i: usize = 1;
-				while i < args.len() {
-					let j = args[i].as_number();
-					if let Token::Number(v) = j {
-
-						if !sum.unit.compatible_with(&v.unit) {
-							return Err(EvalError::IncompatibleUnit);
-						}
-
-						sum += v;
-					} else {
-						panic!();
-					}
-					i += 1;
-				}
-				return Ok(Token::Number(sum));
+			Operator::Negative => {
+				return format!("-{}", self.add_parens_to_arg(&args[0]));
 			},
 
-			Operator::Multiply => {
-				let mut prod = Quantity::new_rational(1f64).unwrap();
-				for i in args.iter() {
-					let j = i.as_number();
-					if let Token::Number(v) = j {
-						prod *= v;
-					} else {
-						panic!();
-					}
-				}
-				return Ok(Token::Number(prod));
+			Operator::ModuloLong => {
+				return format!(
+					"{} mod {}",
+					self.add_parens_to_arg(&args[0]),
+					self.add_parens_to_arg(&args[1])
+				);
 			},
 
-			Operator::ModuloLong
-			| Operator::Modulo => {
-				if args.len() != 2 {panic!()};
-				let a = args[0].as_number();
-				let b = args[1].as_number();
-
-				if let Token::Number(va) = a {
-					if let Token::Number(vb) = b {
-
-						if !(va.unitless() && vb.unitless()) {
-							return Err(EvalError::IncompatibleUnit);
-						}
-
-						if vb <= Quantity::new_rational(1f64).unwrap() { return Err(EvalError::BadMath); }
-						if va.fract() != Quantity::new_rational(0f64).unwrap() { return Err(EvalError::BadMath); }
-						if vb.fract() != Quantity::new_rational(0f64).unwrap() { return Err(EvalError::BadMath); }
-
-						return Ok(Token::Number(va%vb));
-					} else { panic!(); }
-				} else { panic!(); }
+			Operator::UnitConvert => {
+				return format!(
+					"{} to {}",
+					self.add_parens_to_arg(&args[0]),
+					self.add_parens_to_arg(&args[1])
+				);
 			},
 
-			Operator::UnitConvert
-			=> {
-				if args.len() != 2 {panic!()};
-				let a = args[0].as_number();
-				let b = args[1].as_number();
-
-				if let Token::Number(va) = a {
-					if let Token::Number(vb) = b {
-						let n = va.convert_to(vb);
-						if n.is_none() {
-							return Err(EvalError::IncompatibleUnit);
-						}
-						return Ok(Token::Number(n.unwrap()));
-					} else { panic!(); }
-				} else { panic!(); }
+			Operator::Modulo => {
+				return format!(
+					"{} % {}",
+					self.add_parens_to_arg(&args[0]),
+					self.add_parens_to_arg(&args[1])
+				);
 			},
 
 			Operator::Power => {
-				if args.len() != 2 {panic!()};
-				let a = args[0].as_number();
-				let b = args[1].as_number();
-
-				if let Token::Number(va) = a {
-					if let Token::Number(vb) = b {
-
-						if !vb.unitless() {
-							return Err(EvalError::IncompatibleUnit);
-						}
-
-						if va.is_zero() && vb.is_negative() {
-							return Err(EvalError::ZeroDivision);
-						}
-
-						let p = va.pow(vb);
-						if p.is_nan() {return Err(EvalError::BadMath);}
-						return Ok(Token::Number(p));
-					} else { panic!(); }
-				} else { panic!(); }
+				return format!(
+					"{}^{}",
+					self.add_parens_to_arg_strict(&args[0]),
+					self.add_parens_to_arg_strict(&args[1])
+				);
 			},
 
 			Operator::Factorial => {
-				if args.len() != 1 {panic!()};
-				let args = args[0].as_number();
-
-				if let Token::Number(v) = args {
-
-					if !v.unitless() {
-						return Err(EvalError::IncompatibleUnit);
-					}
-
-					if !v.fract().is_zero() { return Err(EvalError::BadMath); }
-					if v > Quantity::new_rational(50_000f64).unwrap() { return Err(EvalError::TooBig); }
-
-					let mut prod = Quantity::new_rational(1f64).unwrap();
-					let mut u = v.clone();
-					while u > Quantity::new_rational(0f64).unwrap() {
-						prod *= u.clone();
-						u = u - Quantity::new_rational(1f64).unwrap();
-					}
-
-					return Ok(Token::Number(prod));
-				} else { panic!(); }
+				return format!("{}!", self.add_parens_to_arg(&args[0]));
 			},
 
-			Operator::Function(f) => {
-				return f.apply(args);
+			Operator::Add => {
+				let a = &args[0];
+
+				let b; let sub;
+				if let Token::Operator(o,ar) = &args[1] {
+					if let Operator::Negative = o {
+						sub = true;
+						b = &ar[0];
+					} else { sub = false; b = &args[1]; }
+				} else { sub = false; b = &args[1]; }
+
+				if sub {
+					return format!(
+						"{} - {}",
+						self.add_parens_to_arg(a),
+						self.add_parens_to_arg(b)
+					);
+				} else {
+					return format!(
+						"{} + {}",
+						self.add_parens_to_arg(a),
+						self.add_parens_to_arg(b)
+					);
+				}
+			},
+
+			Operator::Multiply => {
+				let a = &args[0];
+
+				let b; let div;
+				if let Token::Operator(o,ar) = &args[1] {
+					if let Operator::Flip = o {
+						div = true;
+						b = &ar[0];
+					} else { div = false; b = &args[1]; }
+				} else { div = false; b = &args[1]; }
+
+				if div {
+					return format!("{} ÷ {}",
+						self.add_parens_to_arg_strict(a),
+						self.add_parens_to_arg_strict(b)
+					);
+				} else {
+					return format!("{} × {}",
+						self.add_parens_to_arg_strict(a),
+						self.add_parens_to_arg_strict(b)
+					);
+				}
+			},
+
+			Operator::Function(s) => {
+				return format!("{}({})", s.to_string(), args[0].to_string());
 			}
 		};
 	}
 
+
 }
\ No newline at end of file
diff --git a/src/parser/token/token.rs b/src/parser/token/token.rs
new file mode 100644
index 0000000..23a6b33
--- /dev/null
+++ b/src/parser/token/token.rs
@@ -0,0 +1,56 @@
+use std::collections::VecDeque;
+use crate::quantity::Quantity;
+
+use super::Operator;
+use super::Constant;
+
+/// Tokens represent logical objects in an expession.
+#[derive(Debug)]
+#[derive(Clone)]
+pub enum Token {
+	Quantity(Quantity),
+	Constant(Constant),
+	Operator(Operator, VecDeque<Token>),
+}
+
+impl ToString for Token {
+	fn to_string(&self) -> String {
+		match self {
+			Token::Quantity(v) => v.to_string(),
+			Token::Constant(c) => c.to_string(),
+			Token::Operator(o,a) => o.print(a)
+		}
+	}
+}
+
+impl Token {
+	// This is called only when this is the outermost token.
+	// This sometimes leads to different--usually more verbose--behavior.
+	pub fn to_string_outer(&self) -> String {
+		match self {
+			Token::Quantity(v) => v.to_string_outer(),
+			Token::Constant(c) => c.to_string(),
+			Token::Operator(o,a) => o.print(a)
+		}
+	}
+
+	#[inline(always)]
+	pub fn get_args_mut(&mut self) -> Option<&mut VecDeque<Token>> {
+		match self {
+			Token::Operator(_, ref mut a) => Some(a),
+			_ => None
+		}
+	}
+
+	#[inline(always)]
+	pub fn get_at_coords<'a>(g: &'a mut Token, coords: &Vec<usize>) -> &'a mut Token {
+		let mut h = &mut *g;
+
+		for t in coords.iter() {
+			let inner = h.get_args_mut().unwrap();
+			h = &mut inner[*t];
+		}
+
+		return h;
+	}
+}
\ No newline at end of file
diff --git a/src/tests.rs b/src/tests.rs
index 92d5b10..358403b 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -1,5 +1,6 @@
 // Many of these have been borrowed from insect.
 use crate::parser;
+use crate::evaluate::evaluate;
 
 fn eval_to_str(s: &str) -> Result<String, ()> {
 	let g = match parser::parse(&String::from(s)) {
@@ -8,7 +9,7 @@ fn eval_to_str(s: &str) -> Result<String, ()> {
 	};
 	//let out_str = g.print();
 
-	return match g.evaluate() {
+	return match evaluate(&g) {
 		Ok(x) => Ok(x.to_string_outer()),
 		Err(_) => Err(())
 	};
diff --git a/src/tokens/function.rs b/src/tokens/function.rs
deleted file mode 100644
index d0d2000..0000000
--- a/src/tokens/function.rs
+++ /dev/null
@@ -1,154 +0,0 @@
-use std::collections::VecDeque;
-
-use crate::tokens::Token;
-use crate::tokens::EvalError;
-use crate::tokens::Operator;
-
-#[derive(Debug)]
-#[derive(Copy, Clone)]
-pub enum Function {
-	Abs,
-	Floor,
-	Ceil,
-	Round,
-
-	NaturalLog,
-	TenLog,
-
-	Sin,
-	Cos,
-	Tan,
-	Asin,
-	Acos,
-	Atan,
-	Csc,
-	Sec,
-	Cot,
-
-	Sinh,
-	Cosh,
-	Tanh,
-	Asinh,
-	Acosh,
-	Atanh,
-	Csch,
-	Sech,
-	Coth,
-}
-
-impl Function {
-	pub fn to_string(&self) -> String {
-		match self {
-			Function::Abs => { String::from("abs") },
-			Function::Floor => { String::from("floor") },
-			Function::Ceil => { String::from("ceil") },
-			Function::Round => { String::from("round") },
-			Function::NaturalLog => { String::from("ln") },
-			Function::TenLog => { String::from("log") },
-			Function::Sin => { String::from("sin") },
-			Function::Cos => { String::from("cos") },
-			Function::Tan => { String::from("tan") },
-			Function::Asin => { String::from("asin") },
-			Function::Acos => { String::from("acos") },
-			Function::Atan => { String::from("atan") },
-			Function::Csc => { String::from("csc") },
-			Function::Sec => { String::from("sec") },
-			Function::Cot => { String::from("cot") },
-			Function::Sinh => { String::from("sinh") },
-			Function::Cosh => { String::from("cosh") },
-			Function::Tanh => { String::from("tanh") },
-			Function::Asinh => { String::from("asinh") },
-			Function::Acosh => { String::from("acosh") },
-			Function::Atanh => { String::from("atanh") },
-			Function::Csch => { String::from("csch") },
-			Function::Sech => { String::from("sech") },
-			Function::Coth => { String::from("coth") },
-		}
-	}
-
-	pub fn apply(&self, args: &VecDeque<Token>) -> Result<Token, EvalError> {
-		if args.len() != 1 {panic!()};
-		let a = args[0].as_number();
-		let Token::Number(q) = a else {panic!()};
-
-		if !q.unitless() {
-			return Err(EvalError::IncompatibleUnit);
-		}
-
-		match self {
-			Function::Abs => { return Ok(Token::Number(q.abs())); },
-			Function::Floor => { return Ok(Token::Number(q.floor())); },
-			Function::Ceil => { return Ok(Token::Number(q.ceil())); },
-			Function::Round => { return Ok(Token::Number(q.round())); },
-
-			Function::NaturalLog => { return Ok(Token::Number(q.ln())); },
-			Function::TenLog => { return Ok(Token::Number(q.log10())); },
-
-			Function::Sin => { return Ok(Token::Number(q.sin())); },
-			Function::Cos => { return Ok(Token::Number(q.cos())); },
-			Function::Tan => { return Ok(Token::Number(q.tan())); },
-			Function::Asin => { return Ok(Token::Number(q.asin())); },
-			Function::Acos => { return Ok(Token::Number(q.acos())); },
-			Function::Atan => { return Ok(Token::Number(q.atan())); },
-
-			Function::Csc => {
-				return Ok(
-					Token::Operator(
-						Operator::Flip,
-						VecDeque::from(vec!(Token::Number(q.sin())))
-					).eval()?
-				);
-			},
-			Function::Sec => {
-				return Ok(
-					Token::Operator(
-						Operator::Flip,
-						VecDeque::from(vec!(Token::Number(q.cos())))
-					).eval()?
-				);
-			},
-			Function::Cot => {
-				return Ok(
-					Token::Operator(
-						Operator::Flip,
-						VecDeque::from(vec!(Token::Number(q.tan())))
-					).eval()?
-				);
-			},
-
-
-			Function::Sinh => { return Ok(Token::Number(q.sinh())); },
-			Function::Cosh => { return Ok(Token::Number(q.cosh())); },
-			Function::Tanh => { return Ok(Token::Number(q.tanh())); },
-			Function::Asinh => { return Ok(Token::Number(q.asinh())); },
-			Function::Acosh => { return Ok(Token::Number(q.acosh())); },
-			Function::Atanh => { return Ok(Token::Number(q.atanh())); },
-
-			Function::Csch => {
-				return Ok(
-					Token::Operator(
-						Operator::Flip,
-						VecDeque::from(vec!(Token::Number(q.sinh())))
-					).eval()?
-				);
-			},
-			Function::Sech => {
-				return Ok(
-					Token::Operator(
-						Operator::Flip,
-						VecDeque::from(vec!(Token::Number(q.cosh())))
-					).eval()?
-				);
-			},
-			Function::Coth => {
-				return Ok(
-					Token::Operator(
-						Operator::Flip,
-						VecDeque::from(vec!(Token::Number(q.tanh())))
-					).eval()?
-				);
-			},
-
-		}
-	}
-}
diff --git a/src/tokens/mod.rs b/src/tokens/mod.rs
deleted file mode 100644
index d9dc9f6..0000000
--- a/src/tokens/mod.rs
+++ /dev/null
@@ -1,14 +0,0 @@
-mod function;
-mod operator;
-mod token;
-
-pub use crate::tokens::token::Token;
-pub use crate::tokens::function::Function;
-pub use crate::tokens::operator::Operator;
-
-pub enum EvalError {
-	BadMath,
-	TooBig,
-	ZeroDivision,
-	IncompatibleUnit
-}
\ No newline at end of file
diff --git a/src/tokens/token.rs b/src/tokens/token.rs
deleted file mode 100644
index a2e86cf..0000000
--- a/src/tokens/token.rs
+++ /dev/null
@@ -1,147 +0,0 @@
-use std::collections::VecDeque;
-
-use crate::tokens::EvalError;
-use crate::tokens::Operator;
-use crate::quantity::Quantity;
-
-
-/// Tokens represent logical objects in an expession.
-///
-/// Tokens starting with `Pre*` are intermediate tokens, and
-/// will never show up in a fully-parsed expression tree.
-#[derive(Debug)]
-#[derive(Clone)]
-pub enum Token {
-	Number(Quantity),
-
-	Constant(Quantity, String),
-
-	Operator(
-		Operator,
-		VecDeque<Token>
-	),
-}
-
-impl ToString for Token {
-	fn to_string(&self) -> String {
-		match self {
-			Token::Number(v) => v.to_string(),
-			Token::Constant(_, s) => s.clone(),
-			Token::Operator(o,a) => o.print(a)
-		}
-	}
-}
-
-impl Token {
-
-	// This is called only when this is the outermost token.
-	// This sometimes leads to different--usually more verbose--behavior.
-	pub fn to_string_outer(&self) -> String {
-		match self {
-			Token::Number(v) => v.to_string_outer(),
-			Token::Constant(_, s) => s.clone(),
-			Token::Operator(o,a) => o.print(a)
-		}
-	}
-
-
-	#[inline(always)]
-	pub fn get_args(&self) -> Option<&VecDeque<Token>> {
-		match self {
-			Token::Operator(_, ref a) => Some(a),
-			_ => None
-		}
-	}
-
-	#[inline(always)]
-	pub fn get_args_mut(&mut self) -> Option<&mut VecDeque<Token>> {
-		match self {
-			Token::Operator(_, ref mut a) => Some(a),
-			_ => None
-		}
-	}
-
-	#[inline(always)]
-	pub fn eval(&self) -> Result<Token, EvalError> {
-		Ok(match self {
-			Token::Number(_) => { self.clone() },
-			Token::Constant(v,_) => { Token::Number(v.clone()) },
-			Token::Operator(o,v) => { o.apply(&v)? }
-		})
-	}
-
-	// Temporary solution
-	#[inline(always)]
-	pub fn as_number(&self) -> Token {
-		match self {
-			Token::Number(v) => { Token::Number(v.clone()) },
-			Token::Constant(v,_) => { Token::Number(v.clone()) },
-			_ => panic!()
-		}
-	}
-
-}
-
-
-// Evaluate
-impl Token {
-	#[inline(always)]
-	fn get_at_coords<'a>(g: &'a mut Token, coords: &Vec<usize>) -> &'a mut Token {
-		let mut h = &mut *g;
-
-		for t in coords.iter() {
-			let inner = h.get_args_mut().unwrap();
-			h = &mut inner[*t];
-		}
-
-		return h;
-	}
-
-
-	pub fn evaluate(&self) -> Result<Token, EvalError> {
-		let mut g = self.clone();
-		let mut coords: Vec<usize> = Vec::with_capacity(16);
-		coords.push(0);
-
-		'outer: loop {
-
-			let mut h = &mut g;
-			for t in coords.iter() {
-				let inner = h.get_args_mut();
-
-				if inner.is_none() || *t >= inner.as_ref().unwrap().len() {
-					coords.pop();
-
-
-					let p = Token::get_at_coords(&mut g, &coords);
-					let e = p.eval()?;
-					*p = e;
-
-					if coords.len() == 0 { break 'outer; }
-					let l = coords.pop().unwrap();
-					coords.push(l + 1);
-					continue 'outer;
-				}
-
-				h = &mut inner.unwrap()[*t];
-			}
-
-			match h {
-				Token::Operator(_,_)
-				=> {
-					coords.push(0);
-					continue 'outer;
-				},
-
-				Token::Constant(_,_) |
-				Token::Number(_) => {
-					let l = coords.pop().unwrap();
-					coords.push(l + 1);
-					continue 'outer;
-				}
-			};
-		}
-
-		return Ok(g);
-	}
-}
\ No newline at end of file