1 files changed, 21 insertions, 0 deletions
diff --git a/src/sexp/subst.rs b/src/sexp/subst.rs
new file mode 100644
index 0000000..7cfa180
--- /dev/null
+++ b/src/sexp/subst.rs
@@ -0,0 +1,21 @@
+
+use crate::sexp::{SExp, SExp::*, SLeaf::*, util::*};
+
+impl SExp {
+    /// Performs substitution on the s-expression.
+    ///
+    /// Replaces all free occurrences of variables
+    /// named `name` with the given `value`
+    /// in this s-expression.
+    /// ```rust
+    /// use melisp::sexp::{SExp::*, SLeaf::*, util::*};
+    /// 
+    /// assert_eq!(
+    ///     scons(Add, scons(var("a"), var("b"))).subst("b", scons(Sub, scons(2, 1))),
+    ///     scons(Add, scons(var("a"), scons(Sub, scons(2, 1))))
+    /// );
+    /// ```
+    pub fn subst(self, name: &str, value: SExp) -> SExp {
+        todo!();
+    }
+}