Added boilerplate and tests for let-binds

3 files changed, 33 insertions, 0 deletions

diff --git a/src/sexp/display.rs b/src/sexp/display.rs
index 57d1b50..c3db144 100644
--- a/src/sexp/display.rs
+++ b/src/sexp/display.rs
@@ -27,6 +27,7 @@ impl fmt::Display for SLeaf {
             Var(s) => s.to_string(),
             Quote  => "quote".to_string(),
             Vector => "vector".to_string(),
+            Let    => "let".to_string(),
             Nil    => "()".to_string(),
         })
     }
diff --git a/src/sexp/mod.rs b/src/sexp/mod.rs
index 07d8373..4e3c11c 100644
--- a/src/sexp/mod.rs
+++ b/src/sexp/mod.rs
@@ -31,6 +31,8 @@ pub enum SLeaf {
     Quote,
     Vector,
 
+    Let,
+
     Int(i32),
     True,
     False,
diff --git a/src/sexp/step.rs b/src/sexp/step.rs
index 535b183..e031fca 100644
--- a/src/sexp/step.rs
+++ b/src/sexp/step.rs
@@ -237,6 +237,36 @@ impl SExp {
     ///     scons(2, Nil))).step(),
     ///     Ok(scons(Vector, scons(1, scons(2, Nil))))
     /// );
+    /// ```
+    ///
+    /// **Let-bindings**
+    /// ```rust
+    /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
+    ///
+    /// assert_eq!(
+    ///     scons(
+    ///         scons(Let, scons(var("x"), scons(5, Nil))), scons(
+    ///             scons(Add, scons(var("x"), scons(1, Nil))), Nil
+    ///         )
+    ///     ).step(),
+    ///     Ok(scons(Add, scons(5, scons(1, Nil))))
+    /// );
+    /// assert_eq!(
+    ///     scons(
+    ///         scons(Let, scons(var("y"), scons(4, Nil))),
+    ///         scons(
+    ///             scons(Let, scons(var("x"), scons(5, Nil))),
+    ///             scons(scons(Add, scons(var("x"), scons(var("y"), Nil))), Nil)
+    ///         )
+    ///     ).step(),
+    ///     Ok(scons(
+    ///         scons(Let, scons(var("x"), scons(5, Nil))), scons(
+    ///             scons(Add, scons(var("x"), scons(1, Nil))), Nil
+    ///         )
+    ///     ))
+    /// );
+    /// ```
+    /// 
     pub fn step(self) -> Result<Self, String> {
         match self {