Get rid of ReducedAST unit

Treat it as the empty tuple instead

schala-lang/language/src/eval/mod.rs

@@ -118,7 +118,7 @@ impl Expr {
 
     match self {
       ConditionalTargetSigilValue => replacement.clone(),
-      Unit | Lit(_) | Func(_) | Sym(_) | Constructor { .. } |
+      Lit(_) | Func(_) | Sym(_) | Constructor { .. } |
        CaseMatch { .. } | UnimplementedSigilValue | ReductionError(_) => self,
       Tuple(exprs) => Tuple(exprs.into_iter().map(|e| e.replace_conditional_target_sigil(replacement)).collect()),
       Call { f, args } => {
@@ -186,7 +186,7 @@ impl<'a> State<'a> {
     for stmt in stmts {
       ret = self.statement(stmt)?;
     }
-    Ok(ret.unwrap_or(Node::Expr(Expr::Unit)))
+    Ok(ret.unwrap_or(Node::Expr(Expr::unit())))
   }
 
   fn expression(&mut self, node: Node) -> EvalResult<Node> {
@@ -210,7 +210,6 @@ impl<'a> State<'a> {
         },
         Conditional { box cond, then_clause, else_clause } => self.conditional(cond, then_clause, else_clause),
         Assign { box val, box expr } => self.assign_expression(val, expr),
-        Unit => Ok(Node::Expr(Unit)),
         CaseMatch { box cond, alternatives } => self.case_match_expression(cond, alternatives),
         ConditionalTargetSigilValue => Ok(Node::Expr(ConditionalTargetSigilValue)),
         UnimplementedSigilValue => Err("Sigil value eval not implemented".to_string()),
@@ -331,11 +330,11 @@ impl<'a> State<'a> {
       /* builtin functions */
       (IOPrint, &[ref anything]) => {
         print!("{}", anything.to_repl());
-        Expr::Unit.to_node()
+        Expr::unit().to_node()
       },
       (IOPrintLn, &[ref anything]) => {
         println!("{}", anything.to_repl());
-        Expr::Unit.to_node()
+        Expr::unit().to_node()
       },
       (IOGetLine, &[]) => {
         let mut buf = String::new();
@@ -370,7 +369,7 @@ impl<'a> State<'a> {
     }
     let val = self.expression(Node::Expr(expr))?;
     self.values.insert(name, ValueEntry::Binding { constant: false, val });
-    Ok(Node::Expr(Expr::Unit))
+    Ok(Node::Expr(Expr::unit()))
   }
 
   fn guard_passes(&mut self, guard: &Option<Expr>, cond: &Node) -> EvalResult<bool> {

schala-lang/language/src/eval/test.rs

@@ -30,7 +30,7 @@ macro_rules! test_in_fresh_env {
 #[test]
 fn test_basic_eval() {
   test_in_fresh_env!("1 + 2", "3");
-  test_in_fresh_env!("let mut a = 1; a = 2", "Unit");
+  test_in_fresh_env!("let mut a = 1; a = 2", "()");
   /*
      test_in_fresh_env!("let mut a = 1; a = 2; a", "2");
      test_in_fresh_env!(r#"("a", 1 + 2)"#, r#"("a", 3)"#);

schala-lang/language/src/reduced_ast/types.rs

@@ -23,7 +23,6 @@ pub enum Stmt {
 
 #[derive(Debug, Clone)]
 pub enum Expr {
-    Unit,
     Lit(Lit),
     Sym(Rc<String>), //a Sym is anything that can be looked up by name at runtime - i.e. a function or variable address
     Tuple(Vec<Expr>),
@@ -56,6 +55,13 @@ pub enum Expr {
     ReductionError(String),
 }
 
+impl Expr {
+    // The unit value is an empty tuple
+    pub fn unit() -> Expr {
+        Expr::Tuple(vec![])
+    }
+}
+
 pub type BoundVars = Vec<Option<Rc<String>>>; //remember that order matters here
 
 #[derive(Debug, Clone)]