Implemented let-bindings

1 files changed, 8 insertions, 1 deletions

diff --git a/src/sexp/subst.rs b/src/sexp/subst.rs
index 87f9b50..4cfa48d 100644
--- a/src/sexp/subst.rs
+++ b/src/sexp/subst.rs
@@ -17,7 +17,14 @@ impl SExp {
     /// ```
     pub fn subst(self, name: &str, value: &SExp) -> SExp {
         match self {
-            SCons(a, b) => scons((*a).subst(name, value), (*b).subst(name, value)),
+            SCons(a, b) => {
+                if let Some((varname, _)) = a.clone().check_let() {
+                    if &varname == name {
+                        return SCons(a, b);
+                    }
+                }
+                scons((*a).subst(name, value), (*b).subst(name, value))
+            },
             Atom(Var(x)) if x == name => value.clone(),
             t => t,
         }