From 4df9192586cb1b24678a0b3cb31f3ee4b7d84484 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Thu, 1 Aug 2024 16:56:08 +1000
Subject: [PATCH] xo-parser: feature: def may omit explicit type

---
 include/xo/parser/parser.hpp | 10 +++-------
 src/parser/parser.cpp        | 24 +++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/xo/parser/parser.hpp b/include/xo/parser/parser.hpp
index 75dd22dd..e4e8943a 100644
--- a/include/xo/parser/parser.hpp
+++ b/include/xo/parser/parser.hpp
@@ -141,14 +141,10 @@ namespace xo {
 
             /** scaffold a define-expression here **/
             rp<DefineExprAccess> def_expr_;
-            rp<ConvertExprAccess> cvt_expr_;
-
-#ifdef OBSOLETE
-            /** e.g. f64 in
-             *    def foo : f64 = 1
+            /** scafford a convert-expression here.
+             *  May be nested within a def_expr
              **/
-            TypeDescr def_lhs_td_ = nullptr;
-#endif
+            rp<ConvertExprAccess> cvt_expr_;
         }; /*exprstate*/
 
         inline std::ostream &
diff --git a/src/parser/parser.cpp b/src/parser/parser.cpp
index eef5f821..79c9b73f 100644
--- a/src/parser/parser.cpp
+++ b/src/parser/parser.cpp
@@ -194,8 +194,27 @@ namespace xo {
         exprstate::admits_singleassign() const {
             switch(exs_type_) {
             case exprstatetype::expect_toplevel_expression_sequence:
+
+                /*
+                 *   def foo       = 1
+                 *   def foo : f64 = 1
+                 *  ^   ^   ^ ^   ^ ^ ^
+                 *  |   |   | |   | | (done)
+                 *  |   |   | |   | def_4:expect_rhs_expression
+                 *  |   |   | |   def_3
+                 *  |   |   | def_2:expect_type
+                 *  |   |   def_1
+                 *  |   def_0:expect_symbol
+                 *  expect_toplevel_expression_sequence
+                 *
+                 * note that we skip from def_1 -> def_4 if '=' instead of ':'
+                 */
             case exprstatetype::def_0:
+                return false;
+
             case exprstatetype::def_1:
+                return true;
+
             case exprstatetype::def_2:
                 return false;
 
@@ -203,6 +222,7 @@ namespace xo {
                 return true;
 
             case exprstatetype::def_4:
+
             case exprstatetype::expect_rhs_expression:
                 /* rhs-expressions (or expressions for that matter)
                  * may not begin with singleassign '='
@@ -437,7 +457,9 @@ namespace xo {
                                                xtag("state", *this)));
             }
 
-            if (this->exs_type_ == exprstatetype::def_3) {
+            if ((this->exs_type_ == exprstatetype::def_1)
+                || (this->exs_type_ == exprstatetype::def_3))
+            {
                 this->exs_type_ = exprstatetype::def_4;
 
                 p_stack->push_exprstate(exprstatetype::expect_rhs_expression);