feat: Add a `Display` impl for `SimpleType`

Fixes https://github.com/Nadrieril/dhall-rust/issues/179

2 files changed, 23 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2b6388f..f976b59 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 #### [Unreleased]
 
+- Add a `Display` impl for `SimpleType` (https://github.com/Nadrieril/dhall-rust/issues/179)
+
 #### [0.7.0] - 2020-09-15
 
 - BREAKING CHANGE: Support Dhall v18.0.0
diff --git a/serde_dhall/src/value.rs b/serde_dhall/src/value.rs
index 0f0b256..b26985b 100644
--- a/serde_dhall/src/value.rs
+++ b/serde_dhall/src/value.rs
@@ -290,6 +290,11 @@ impl SimpleType {
             ),
         })
     }
+
+    /// Converts back to the corresponding AST expression.
+    pub(crate) fn to_expr(&self) -> Expr {
+        self.to_hir().to_expr(Default::default())
+    }
 }
 
 impl Sealed for Value {}
@@ -336,3 +341,19 @@ impl std::fmt::Display for Value {
         self.to_expr().fmt(f)
     }
 }
+
+impl std::fmt::Display for SimpleType {
+    fn fmt(
+        &self,
+        f: &mut std::fmt::Formatter,
+    ) -> std::result::Result<(), std::fmt::Error> {
+        self.to_expr().fmt(f)
+    }
+}
+
+#[test]
+fn test_display_simpletype() {
+    use SimpleType::*;
+    let ty = List(Box::new(Optional(Box::new(Natural))));
+    assert_eq!(ty.to_string(), "List (Optional Natural)".to_string())
+}