Changed UndefinedType to VarType(String) for generics and added tests for inferring them.

Inferring is done by method Type::infer_generics.
Whether it is executed is controlled by method Type::is_concrete.
Also had to change the Display for Type and its tests,
as the enum variants changed.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/type/display.rs b/src/type/display.rs
index 781d614..be51858 100644
--- a/src/type/display.rs
+++ b/src/type/display.rs
@@ -26,7 +26,7 @@ impl fmt::Display for Type {
                                     .collect::<Vec<String>>()
                                     .join(" ")
                            ),
-            UndefinedType => write!(f, "?"),
+            VarType(name) => write!(f, "{}", name),
         }
     }
 }
@@ -47,7 +47,7 @@ impl fmt::Display for TypeError {
     /// assert_eq!(
     ///     InvalidOperator {
     ///         operator: Atom(Int(1)),
-    ///         expected: arr(UndefinedType, UndefinedType),
+    ///         expected: arr(VarType("?".to_string()), VarType("?".to_string())),
     ///         found:    Integer
     ///     }.to_string(),
     ///     "invalid operator: '1'\nexpected: '? -> ?'\nfound: 'Int'".to_string()
@@ -60,10 +60,15 @@ impl fmt::Display for TypeError {
     ///     }.to_string(),
     ///     "invalid argument list: '(1 2 3)'\nexpected: '(Int Int)'\nfound: '(Int Int Int)'".to_string()
     /// );
+    /// assert_eq!(
+    ///     UnboundGeneric(String::from("?")).to_string(),
+    ///     "unbound generic type: '?'".to_string()
+    /// );
     /// ```
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             UndefinedVariable(name) => write!(f, "undefined variable: '{}'", name),
+            UnboundGeneric(name)    => write!(f, "unbound generic type: '{}'", name),
             InvalidOperator { operator, expected, found } => {
                 write!(
                     f,