Couple more tweaks to number printing

types/src/number/mod.rs

@@ -66,10 +66,8 @@ impl Number {
 
 impl fmt::Display for Number {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", self.real).and_then(|r| match self.imag {
-            Some(ref imag) => write!(f, "{}i", imag),
-            None => Ok(r),
-        })
+        write!(f, "{}", self.real).and_then(
+            |r| self.imag.map(|i| write!(f, "{:+}i", i)).unwrap_or(Ok(r)))
     }
 }
 

types/src/number/real.rs

@@ -130,6 +130,7 @@ impl PartialEq for Real {
 
 impl fmt::Display for Real {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // TODO: Figure out how to print the sign if `f.sign_plus() == true`.
         match *self {
             Real::Integer(v) => write!(f, "{}", v),
             Real::Rational(p, q) => write!(f, "{}/{}", p, q),