Added boilerplate and tests for let-binds

1 files changed, 38 insertions, 0 deletions

diff --git a/src/type/check.rs b/src/type/check.rs
index df3f4d9..d0ce807 100644
--- a/src/type/check.rs
+++ b/src/type/check.rs
@@ -81,6 +81,43 @@ impl SExp {
     /// assert_eq!(Atom(Not).type_check(), Ok(arr(List(vec![Boolean]), Boolean)));
     /// ```
     ///
+    ///
+    /// **Let-binding types**
+    ///
+    /// Let-bindings are quite interesting. Implementation is still a bit uncertain,
+    /// but at least we know that
+    /// ```rust
+    /// use myslip::{
+    ///     r#type::{*, Type::*, TypeError::*, util::*},
+    ///     sexp::{SExp::*, SLeaf::*, util::*},
+    /// };
+    ///
+    /// assert_eq!(
+    ///     scons(
+    ///         scons(Let, scons(var("x"), scons(False, Nil))),
+    ///         scons(var("x"), Nil)
+    ///     ).type_check(),
+    ///     Ok(Boolean)
+    /// );
+    /// ```
+    ///
+    /// As such it must be that the type of the let-binding s-expression is st.
+    /// ```rust
+    /// use myslip::{
+    ///     r#type::{*, Type::*, TypeError::*, util::*},
+    ///     sexp::{SExp::*, SLeaf::*, util::*},
+    /// };
+    ///
+    /// assert_eq!(
+    ///     scons(Let, scons(var("x"), scons(1, Nil))).type_check(),
+    ///     Ok(arr(vt("T"), vt("T")))
+    /// );
+    /// ```
+    /// ie. the identity function.
+    ///
+    /// No more behavior on typing let can be defined, as typing the let-keyword
+    /// would require the yet untyped variable to be typed.
+    ///
     /// Though perhaps the most important task of the type system
     /// is to increase safety by being able to warn about errors
     /// before evaluation. Here are some failing examples:
@@ -173,6 +210,7 @@ impl SExp {
                                 vecof(vt("T")),
                                 List(vec![VecType, vecof(vt("T"))])
                             )),
+            Atom(Let)    => todo!(),
 
 
             SCons(op, l) => {