improve do & recur errs

src/main.rs

@@ -167,10 +167,7 @@ pub fn run(src: &'static str) {
 
 pub fn main() {
     let src = "
-match foo with {
+do 42 > recur ()
-    :a -> :b
-    :c -> :d
-}
     ";
     run(src);
     // struct_scalpel::print_dissection_info::<value::Value>()

src/validator.rs

@@ -282,6 +282,8 @@ impl<'a> Validator<'a> {
                         self.ast = expr;
                         self.span = *span;
                         self.validate();
+
+                        //TODO: check arity of call
                     }
                     _ => unreachable!(),
                 }
@@ -389,13 +391,25 @@ impl<'a> Validator<'a> {
                 self.validate();
                 self.status.tail_position = tailpos;
             }
+            // TODO: fix the tail call here?
             Ast::Do(terms) => {
-                for term in terms {
+                if terms.len() < 2 {
+                    return self.err("do expressions must have at least two terms".to_string());
+                }
+                for term in terms.iter().take(terms.len() - 1) {
                     let (expr, span) = term;
                     self.ast = expr;
                     self.span = *span;
                     self.validate();
                 }
+
+                let (expr, span) = terms.last().unwrap();
+                self.ast = expr;
+                self.span = *span;
+                if matches!(expr, Ast::Recur(_)) {
+                    self.err("`recur` may not be used in `do` forms".to_string());
+                }
+                self.validate();
             }
             Ast::Repeat(times, body) => {
                 self.status.tail_position = false;
@@ -427,7 +441,8 @@ impl<'a> Validator<'a> {
             }
             Ast::Recur(args) => {
                 if !self.status.in_loop {
-                    self.err("you may only use `recur` in a loop form".to_string());
+                    self.err("you may only use `recur` in a `loop` form".to_string());
+                    return;
                 }
                 if !self.status.tail_position {
                     self.err("you may only use `recur` in tail position".to_string());