Cleanup for 'be' statement and comments about future typestate

src/comp/front/ast.rs

@@ -315,6 +315,17 @@ fn index_native_item(native_mod_index index, @native_item it) {
     }
 }
 
+fn is_call_expr(@expr e) -> bool {
+    alt (e.node) {
+        case (expr_call(_, _, _)) {
+            ret true;
+        }
+        case (_) {
+            ret false;
+        }
+    }
+}
+
 //
 // Local Variables:
 // mode: rust

src/comp/front/parser.rs

@@ -1203,7 +1203,13 @@ impure fn parse_stmt(parser p) -> @ast.stmt {
         case (token.BE) {
             p.bump();
             auto e = parse_expr(p);
-            ret @spanned(lo, e.span, ast.stmt_be(e));
+            // FIXME: Is this the right place for this check?
+            if /*check*/ (ast.is_call_expr(e)) {
+                ret @spanned(lo, e.span, ast.stmt_be(e));
+            }
+            else {
+                p.err("Non-call expression in tail call");
+            }
         }
 
         case (token.LET) {

src/comp/middle/trans.rs

@@ -3129,7 +3129,10 @@ fn trans_ret(@block_ctxt cx, &option.t[@ast.expr] e) -> result {
 }
 
 fn trans_be(@block_ctxt cx, @ast.expr e) -> result {
-    // FIXME: So this isn't actually a tail call
+    // FIXME: This should be a typestate precondition
+    check ast.is_call_expr(e);
+    // FIXME: Turn this into a real tail call once
+    // calling convention issues are settled
     ret trans_ret(cx, some(e));
 }
 

src/comp/middle/typeck.rs

@@ -1720,18 +1720,12 @@ fn check_stmt(&@fn_ctxt fcx, &@ast.stmt stmt) -> @ast.stmt {
         }
 
         case (ast.stmt_be(?expr)) {
-            alt (expr.node) {
-                case (ast.expr_call(_, _, _)) {
-                    auto expr_0 = check_expr(fcx, expr);
-                    auto expr_1 = demand_expr(fcx, fcx.ret_ty, expr_0);
-                    ret @fold.respan[ast.stmt_](stmt.span,
-                                                ast.stmt_be(expr_1));
-                }
-                case (_) {
-                    fcx.ccx.sess.err("Non-call expression in tail call");
-                    fail;
-                }
-            }
+            /* FIXME: prove instead of check */
+            check ast.is_call_expr(expr);
+            auto expr_0 = check_expr(fcx, expr);
+            auto expr_1 = demand_expr(fcx, fcx.ret_ty, expr_0);
+            ret @fold.respan[ast.stmt_](stmt.span,
+                                        ast.stmt_be(expr_1));
         }
 
         case (ast.stmt_log(?expr)) {

src/test/compile-fail/tail-non-call.rs

@@ -7,4 +7,4 @@ fn f() -> int {
 
 fn main() {
   auto y = f();
-}
+}

src/test/compile-fail/tail-typeck.rs

@@ -10,4 +10,4 @@ fn g() -> uint {
 
 fn main() {
   auto y = f();
-}
+}