2 files changed, 47 insertions, 0 deletions
diff --git a/src/sexp/display.rs b/src/sexp/display.rs
new file mode 100644
index 0000000..e6dbb7c
--- /dev/null
+++ b/src/sexp/display.rs
@@ -0,0 +1,45 @@
+
+use std::fmt;
+use crate::sexp::{SLeaf, SExp, SLeaf::*, SExp::*, util::*};
+
+
+impl fmt::Display for SLeaf {
+
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", match self {
+            Add    => "+".to_string(),
+            Sub    => "-".to_string(),
+            Mul    => "*".to_string(),
+            Div    => "/".to_string(),
+            Int(x) => x.to_string(),
+            Var(s) => s.to_string(),
+            Quote  => "quote".to_string(),
+            Nil    => "()".to_string(),
+        })
+    }
+
+}
+
+
+impl fmt::Display for SExp {
+
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Atom(leaf) => write!(f, "{}", leaf.to_string()),
+            SCons(a, b) => {
+                match scons(a.clone(), b.clone()).into_vec() {
+                    Ok(l) => write!(
+                        f,
+                        "({})",
+                        l.into_iter()
+                         .map(|x| x.to_string())
+                         .collect::<Vec<String>>()
+                         .join(" ")
+                    ),
+                    Err(_) => write!(f, "({} {})", *a, *b),
+                }
+            }
+        }
+    }
+
+}
diff --git a/src/sexp/mod.rs b/src/sexp/mod.rs
index 71e62e9..0fb5e25 100644
--- a/src/sexp/mod.rs
+++ b/src/sexp/mod.rs
@@ -2,6 +2,7 @@
 pub mod step;
 pub mod util;
 pub mod subst;
+pub mod display;
 
 /// A leaf node for S-Expressions.
 ///
@@ -36,6 +37,7 @@ pub enum SExp {
 use SExp::*;
 use SLeaf::*;
 
+
 impl SExp {
     pub fn is_value(&self) -> bool {
         match self {