1 files changed, 49 insertions, 0 deletions
diff --git a/src/sexp/step.rs b/src/sexp/step.rs
new file mode 100644
index 0000000..86ad9ea
--- /dev/null
+++ b/src/sexp/step.rs
@@ -0,0 +1,49 @@
+
+use crate::sexp::SExp;
+
+impl SExp {
+
+    /// Evaluates the s-expression one step.
+    ///
+    /// **Integer operations**
+    ///
+    /// Addition, subtraction, multiplication and division
+    /// are supported.
+    /// ```rust
+    /// use melisp::sexp::{SExp::*, SLeaf::*, util::*};
+    ///
+    /// assert_eq!(
+    ///     sexp(Add, sexp(1, 1)).step().unwrap(),
+    ///     Atom(Int(2))
+    /// );
+    ///
+    /// assert_eq!(
+    ///     sexp(Sub, sexp(1, 2).step().unwrap()),
+    ///     Atom(Int(-1))
+    /// );
+    ///
+    /// assert_eq!(
+    ///     sexp(Mul, sexp(2, 3).step().unwrap()),
+    ///     Atom(Int(6))
+    /// );
+    ///
+    /// assert_eq!(
+    ///     sexp(Div, sexp(6, 2).step().unwrap()),
+    ///     Atom(Int(3))
+    /// );
+    /// ```
+    ///
+    /// Division truncates the decimals.
+    /// ```rust
+    /// use melisp::sexp::{SExp::*, SLeaf::*, util::*};
+    ///
+    /// assert_eq!(
+    ///     sexp(Div, sexp(5, 2).step().unwrap()),
+    ///     Atom(Int(2))
+    /// );
+    ///
+    /// ```
+    pub fn step(self) -> Result<Self, String> {
+        todo!();
+    }
+}