Implement support for cond resolves #4

src/environment.rs

@@ -5,6 +5,7 @@ use std::mem;
 
 type Mapping = (Datum, Datum);
 
+#[derive(Debug)]
 pub struct Frame<'a> {
     mappings: Vec<Mapping>,
     outer: Option<&'a Frame<'a>>,

src/interpreter.rs

@@ -83,8 +83,17 @@ fn interpret_define(args: &Vec<Datum>, env: &mut Env) -> Datum {
     }
 }
 
-fn interpret_cond(_vec: &Vec<Datum>, _env: &mut Env) -> Datum {
-    Datum::Unspecified
+fn interpret_cond(vec: &Vec<Datum>, env: &mut Env) -> Datum {
+    for i in 1..vec.len() {
+        if let List(v) = &vec[i] {
+            if has_tag(v, "else") || is_true(&interpret(&v[0], env)) {
+                return interpret_begin(v, env);
+            }
+        } else {
+            panic!("INTERPRET-COND -- not a list {:?}", vec[i])
+        }
+    }
+    panic!("INTERPRET-COND -- missing else statement? {:?}", vec)
 }
 
 fn interpret_begin(vec: &Vec<Datum>, env: &mut Env) -> Datum {

src/primitives.rs

@@ -94,7 +94,7 @@ pub fn display(args: Vec<Datum>) -> Datum {
             Number(n) => print!("{}", n),
             String(s) => print!("{}", s),
             List(v) => print!("{:?}", v),
-            _ => panic!("DISPLAY -- cannot-print {:?}", args[1]),
+            _ => panic!("DISPLAY -- cannot-print {:?}", args[i]),
         };
     }
     io::stdout().flush().ok().expect("Could not flush stdout");