Integer and Rational correctly report exactness

types/src/number/integer.rs

@@ -11,6 +11,8 @@ pub struct Integer(pub Int);
 
 impl Number for Integer {
     fn convert_down(&self) -> Option<Box<Number>> { None }
+
+    fn is_exact(&self) -> bool { true }
 }
 
 impl Value for Integer {
@@ -35,6 +37,7 @@ impl ValueEq for Integer {
 #[cfg(test)]
 mod tests {
     use super::Integer;
+    use number::*;
     use value::*;
 
     #[test]
@@ -52,4 +55,10 @@ mod tests {
         assert_eq!(Integer(6).is_char(), false);
         assert_eq!(Integer(6).is_bool(), false);
     }
+
+    #[test]
+    fn integers_are_exact() {
+        assert!(Integer(4).is_exact());
+        assert!(!Integer(4).is_inexact());
+    }
 }

types/src/number/mod.rs

@@ -24,6 +24,14 @@ type Flt = f64;
 trait Number: Debug + IsBool + IsChar + IsNumber + Value {
     /// Convert a Number to the next lowest type in Scheme's number pyramid, if possible.
     fn convert_down(&self) -> Option<Box<Number>>;
+
+    /// Should return `true` if this Number is represented exactly. This should be an inverse of
+    /// `is_inexact()`.
+    fn is_exact(&self) -> bool { false }
+
+    /// Should return `true` if this Number is not represented exactly. This should be an inverse
+    /// of `is_exact()`.
+    fn is_inexact(&self) -> bool { !self.is_exact() }
 }
 
 impl Value for Box<Number> {

types/src/number/rational.rs

@@ -18,6 +18,8 @@ impl Number for Rational {
             None
         }
     }
+
+    fn is_exact(&self) -> bool { true }
 }
 
 impl Value for Rational {
@@ -77,4 +79,10 @@ mod tests {
         let rational_as_integer = Rational(3, 2).convert_down();
         assert!(rational_as_integer.is_none());
     }
+
+    #[test]
+    fn rationals_are_exact() {
+        assert!(Rational(4, 2).is_exact());
+        assert!(!Rational(4, 2).is_inexact());
+    }
 }