2 files changed, 130 insertions, 0 deletions
diff --git a/src/type/conversion.rs b/src/type/conversion.rs
new file mode 100644
index 0000000..128d1aa
--- /dev/null
+++ b/src/type/conversion.rs
@@ -0,0 +1,129 @@
+
+use crate::r#type::Type;
+
+impl Type {
+
+    /// Checks if this type is known as the given other type,
+    /// ie. checks if there exists an implicit conversion from
+    /// one to the other.
+    ///
+    /// Currently this is only needed for list to vec conversions.
+    /// ```rust
+    /// use myslip::r#type::{Type::*, util::*};
+    /// assert!(List(vec![Integer, Integer, Integer]).aka(&vecof(Integer)));
+    /// ```
+    ///
+    /// Preferrably this should also work with generics:
+    /// ```rust
+    /// use myslip::r#type::{Type::*, util::*};
+    /// assert!(List(vec![Integer, Boolean, Integer]).aka(&vecof(vt("T"))));
+    /// assert!(List(vec![Integer, Boolean, vt("X")]).aka(&vecof(vt("T"))));
+    /// ```
+    ///
+    /// But of course it also should know when to fail:
+    /// ```rust
+    /// use myslip::r#type::{Type::*, util::*};
+    /// assert!(!List(vec![Integer, Boolean]).aka(&vecof(Integer)));
+    /// assert!(!List(vec![Integer, Boolean]).aka(&vecof(Boolean)));
+    /// ```
+    pub fn aka(&self, known_as: &Type) -> bool {
+	todo!()
+    }
+
+    fn least_general_supertype(&self, other: &Type) -> Type {
+	todo!()
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::r#type::{Type::*, util::*};
+
+    #[test]
+    fn test_basic_general_supertypes() {
+
+	assert_eq!(Integer.least_general_supertype(&Integer), Integer);
+	assert_eq!(Integer.least_general_supertype(&Boolean), vt("T"));
+
+    }
+
+    #[test]
+    fn test_compound_general_supertypes() {
+
+	assert_eq!(
+	    List(vec![Integer, Integer])
+		.least_general_supertype(
+		    &List(vec![Integer, Integer])
+		),
+	    List(vec![Integer, Integer])
+	);
+
+	assert_eq!(
+	    List(vec![Integer, Boolean])
+		.least_general_supertype(
+		    &List(vec![Integer, Integer])
+		),
+	    List(vec![Integer, vt("T")])
+	);
+
+	assert_eq!(
+	    vecof(Integer)
+		.least_general_supertype(
+		    &vecof(Integer)
+		),
+	    vecof(Integer)
+	);
+
+	assert_eq!(
+	    vecof(Integer)
+		.least_general_supertype(
+		    &vecof(Boolean)
+		),
+	    vecof(vt("T"))
+	);
+
+	assert_eq!(
+	    List(vec![Integer, Boolean]).least_general_supertype(
+		&List(vec![Boolean, Integer])
+	    ),
+	    List(vec![vt("T"), vt("T")])
+	);
+
+    }
+
+    #[test]
+    fn test_conversion_in_general_supertypes() {
+
+	assert_eq!(
+	    List(vec![Integer, Integer]).least_general_supertype(
+		&vecof(Integer)
+	    ),
+	    vecof(Integer)
+	);
+
+	assert_eq!(
+	    List(vec![Integer, Integer]).least_general_supertype(
+		&List(vec![Integer, Integer, Integer])
+	    ),
+	    vecof(Integer)
+	);
+
+	assert_eq!(
+	    List(vec![Integer, Boolean]).least_general_supertype(
+		&List(vec![Integer, Boolean, Integer])
+	    ),
+	    vecof(vt("T"))
+	);
+
+	assert_eq!(
+	    List(vec![Boolean, Integer]).least_general_supertype(
+		&vecof(Integer)
+	    ),
+	    vecof(vt("T"))
+	);
+
+    }
+
+}
diff --git a/src/type/mod.rs b/src/type/mod.rs
index afb5a0b..eba817b 100644
--- a/src/type/mod.rs
+++ b/src/type/mod.rs
@@ -4,6 +4,7 @@ pub mod util;
 pub mod display;
 pub mod check;
 pub mod subst;
+pub mod conversion;
 
 
 use crate::sexp::SExp;