Added print, raised level on which UnboundGeneric error is returned

4 files changed, 26 insertions, 1 deletions

diff --git a/src/sexp/display.rs b/src/sexp/display.rs
index c3db144..dc5d6cb 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(),
+            Print  => "print".to_string(),
             Let    => "let".to_string(),
             Nil    => "()".to_string(),
         })
diff --git a/src/sexp/mod.rs b/src/sexp/mod.rs
index 7aa517b..c674ee9 100644
--- a/src/sexp/mod.rs
+++ b/src/sexp/mod.rs
@@ -33,6 +33,8 @@ pub enum SLeaf {
 
     Let,
 
+    Print,
+
     Int(i32),
     True,
     False,
@@ -69,7 +71,7 @@ impl SExp {
             SCons(a, b) =>
                 SCons(a.clone(), b.clone()).check_let().is_some() ||
                 (
-                    (**a == Atom(Quote) || **a == Atom(Vector))
+                    (**a == Atom(Quote) || **a == Atom(Vector) || **a == Atom(Print))
                     && b.consists_of_values()
                 ),
             Atom(Var(_)) => false,
diff --git a/src/sexp/step.rs b/src/sexp/step.rs
index 816582c..94f6381 100644
--- a/src/sexp/step.rs
+++ b/src/sexp/step.rs
@@ -309,6 +309,21 @@ impl SExp {
                 None => panic!("unreachable as per match guard arm"),
             },
 
+            // prints
+            SCons(op, l) if op.clone().is_print() => match *op {
+                SCons(_, b) => {
+                    println!("{}", match *b {
+                        SCons(a, b) if *b == Atom(Nil) => *a,
+                        t => t,
+                    });
+                    Ok(match *l {
+                        SCons(a, b) if *b == Atom(Nil) => *a,
+                        t => t
+                    })
+                },
+                Atom(_) => panic!("unreachable as per match arm guard"),
+            },
+
 
             // op value and a1 .. an values, and b0, b1 .. bn not values
             // ---------------------------------------------------------
diff --git a/src/sexp/util.rs b/src/sexp/util.rs
index a28aaad..507455f 100644
--- a/src/sexp/util.rs
+++ b/src/sexp/util.rs
@@ -86,4 +86,11 @@ impl SExp {
             _ => None
         }
     }
+
+    pub fn is_print(&self) -> bool {
+        match self {
+            SCons(op, _) if **op == Atom(Print) => true,
+            _ => false
+        }
+    }
 }