Cleaned up evaluator

src/evaluate/evaluate.rs

@@ -7,62 +7,57 @@ use super::operator::eval_operator;
 use super::function::eval_function;
 use super::EvalError;
 
-pub fn evaluate(t: &Token, context: &Context) -> Result<Token, EvalError> {
-	let mut g = t.clone();
+pub fn evaluate(t: &Token, context: &mut Context) -> Result<Token, EvalError> {
+
+	// Keeps track of our position in the token tree.
+	// For example, the coordinates [0, 2, 1] are interpreted as follows:
+	// Start at the root node,
+	//    then move to that node's 0th child,
+	//    then move to that node's 2nd child,
+	//    then move to that node's 1st child.
+	//
 	let mut coords: Vec<usize> = Vec::with_capacity(16);
+	let mut root = t.clone();
+
+	// coords points to the *next* node we will move to.
 	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 mut e = p.clone();
-
-				// Evaluate until we get a single number.
-				// This loop is necessary because some eval_* functions
-				// May return an incomplete result.
-				// ( For example, csc(x) is treated as 1/sin(x) )
+	// Repeats while we have coordinates to parse.
+	// Exits when we finish parsing the root node.
 	loop {
-					e = match e {
-						Token::Quantity(_) => { break; },
+		// Current position in the tree
+		let g = root.get_at_coords_mut(&coords[0 .. coords.len() - 1]);
+
+		// "Move up" step.
+		// We move up if we're at a leaf or if we're out of children to move down to.
+		if {
+			g.is_quantity() ||
+			g.get_args().is_none() ||
+			(coords.len() != 0 && (*coords.last().unwrap() >= g.get_args().unwrap().len()))
+		} {
+
+			if !g.is_quantity() {
+				*g = match g {
+					Token::Quantity(_) => panic!(),
+
 					Token::Constant(c) => { evaluate(&c.value(), context).unwrap() },
+					Token::Variable(s) => { context.get_variable(&s).unwrap() },
 					Token::Operator(Operator::Function(f), v) => { eval_function(&f, &v)? },
-						Token::Operator(o, v) => { eval_operator(&o, &v)? },
-						Token::Variable(s) => { context.get_variable(&s).unwrap() }
-					};
+					Token::Operator(o, v) => { eval_operator(&o, &v, context)? },
+				}
 			}
 
-				*p = e;
+			// Move up the tree
+			coords.pop();
+			if coords.len() != 0 {
+				*coords.last_mut().unwrap() += 1;
+			} else { break; }
 
-				if coords.len() == 0 { break 'outer; }
-				let l = coords.pop().unwrap();
-				coords.push(l + 1);
-				continue 'outer;
+		} else {
+			// Move down the tree
+			coords.push(0);
+		}
 	}
 
-			h = &mut inner.unwrap()[*t];
-		}
-
-
-		match h {
-			Token::Operator(_,_)
-			| Token::Constant(_)
-			| Token::Variable(_)
-			=> { coords.push(0); },
-
-			Token::Quantity(_) => {
-				let l = coords.pop().unwrap();
-				coords.push(l + 1);
-			}
-		};
-	}
-
-	return Ok(g);
+	return Ok(root);
 }