Fixed unit matching

src/quantity/quantity.rs

@@ -111,7 +111,6 @@ impl Quantity {
 		return Some(n.mul_no_convert(fa).div_no_convert(fb))
 	}
 
-
 	pub fn match_units(&mut self, other: &Quantity) {
 
 		let mut new_units = Quantity::new_rational_from_string("1").unwrap();
@@ -123,14 +122,15 @@ impl Quantity {
 
 			// Check if `us` matches some unit in `other`
 			for (uo, _) in other.unit.get_val() {
-				if {
-					uo.to_base().unit.compatible_with(&us.to_base().unit)
-				} {
-					// If it does, convert `us` to `uo`
-					new_units.insert_unit(uo.clone(), ps.clone());
-					flag = true;
-					break;
-				}
+				// Use generalized compatible_with check to match reciprocal units
+				// (for example, 1Hz * 1 sec.)
+				let f = uo.to_base().unit.compatible_with_power(&us.to_base().unit);
+				if f.is_none() { continue; }
+				let f = f.unwrap();
+
+				new_units.insert_unit(uo.clone(), ps.clone() * f);
+				flag = true;
+				break;
 			}
 			if !flag {
 				// If no unit in `other` matches `us`, don't convert `us`

src/quantity/unit/unit.rs

@@ -162,6 +162,55 @@ impl Unit {
 		return o == s;
 	}
 
+
+	// True if all base units are the same AND there is a constant factor between their powers.
+	// This is a generalization of `compatible_with`. `compatible_with` is true iff
+	// `compatible_with_power` is one.
+	pub fn compatible_with_power(&self, other: &Unit) -> Option<Scalar> {
+		let mut flag;
+		let mut pow_factor: Option<Scalar> = None;
+
+		let sbu = self.to_base().unit;
+		let obu = other.to_base().unit;
+
+		for (us, ps) in sbu.get_val() {
+			flag = false;
+			for (uo, po) in obu.get_val() {
+				if uo.whole == us.whole {
+					if pow_factor.is_none() {
+						pow_factor = Some(po.clone() / ps.clone());
+					} else if let Some(ref f) = pow_factor {
+						if *f != po.clone() / ps.clone() { return None; }
+					}
+
+					flag = true;
+					break;
+				}
+			}
+			if !flag { return None; }
+		}
+
+		pow_factor = None;
+		for (uo, po) in obu.get_val() {
+			flag = false;
+			for (us, ps) in sbu.get_val() {
+				if uo.whole == us.whole {
+					if pow_factor.is_none() {
+						pow_factor = Some(po.clone() / ps.clone());
+					} else if let Some(ref f) = pow_factor {
+						if *f != po.clone() / ps.clone() { return None; }
+					}
+
+					flag = true;
+					break;
+				}
+			}
+			if !flag { return None; }
+		}
+
+		return pow_factor;
+	}
+
 	pub fn insert(&mut self, u: FreeUnit, p: Scalar) {
 		let v = self.get_val_mut();
 		match v.get_mut(&u) {

src/tests.rs

@@ -211,4 +211,6 @@ fn complex_units() {
 	good_expr("20 mi", "10 mph * 2 hours");
 	good_expr("120 m", "1 (m/s) * 2 min");
 	good_expr("120 m", "(2 min) * (1 m/s)");
+	good_expr("180", "1 Hz * 3 min");
+	good_expr("3600", "1 hour * 1 Hz");
 }