add a `Display` implementation to `Expression` HEAD canon

this change adds a string formatter for `Expression`s using the `Display`
trait. additionally, it standardizes the way `Display` implementations
are written and makes some minor adjustments to the parameters used for
the proptest-based test for `Expression`.

Change-Id: I6a6a6964cd5c04e95341a499dcd73297ca2f514a

1 files changed, 13 insertions, 3 deletions

diff --git a/crates/core/src/numerics/rational.rs b/crates/core/src/numerics/rational.rs
index e814dbd..173e6f6 100644
--- a/crates/core/src/numerics/rational.rs
+++ b/crates/core/src/numerics/rational.rs
@@ -106,6 +106,16 @@ where
     }
 }
 
+#[cfg(feature = "core-fmt")]
+impl<T> fmt::Display for Rational<T>
+where
+    T: Integer + fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}/{}", self.numerator, self.denominator)
+    }
+}
+
 /// Representation of an error that occurred within [`Rational`].
 #[non_exhaustive]
 #[derive(Eq, PartialEq)]
@@ -117,12 +127,12 @@ pub enum Error {
 
 #[cfg(feature = "core-fmt")]
 impl fmt::Display for Error {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
-        fmt.write_str("rational number construction failed")?;
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("rational number construction failed")?;
         let reason = match self {
             Error::ZeroDenominator => " because the denominator was zero",
         };
-        fmt.write_str(reason)
+        f.write_str(reason)
     }
 }