Typed Midrule Actions

NEWS.md

@@ -1,5 +1,45 @@
 # NEWS for Lrama
 
+## Lrama 0.6.5 (2024-03-xx)
+
+### Typed Midrule Actions
+
+User can specify the type of mid rule action by tag (`<bar>`) instead of specifying it with in an action.
+
+```
+primary: k_case expr_value terms?
+           {
+               $<val>$ = p->case_labels;
+               p->case_labels = Qnil;
+           }
+         case_body
+         k_end
+           {
+             ...
+           }
+```
+
+can be written as
+
+```
+primary: k_case expr_value terms?
+           {
+               $$ = p->case_labels;
+               p->case_labels = Qnil;
+           }<val>
+         case_body
+         k_end
+           {
+             ...
+           }
+```
+
+`%destructor` for midrule action is invoked only when tag is specified by Typed Midrule Actions.
+
+Difference from Bison's Typed Midrule Actions is that tag is postposed in Lrama however it's preposed in Bison.
+
+Bison supports this feature from 3.1.
+
 ## Lrama 0.6.4 (2024-03-22)
 
 ### Parameterizing rules (preceded, terminated, delimited)

lib/lrama/grammar/rule_builder.rb

@@ -128,10 +128,11 @@ def process_rhs(parameterizing_rule_resolver)
             end
           when Lrama::Lexer::Token::UserCode
             prefix = token.referred ? "@" : "$@"
+            tag = token.tag || lhs_tag
             new_token = Lrama::Lexer::Token::Ident.new(s_value: prefix + @midrule_action_counter.increment.to_s)
             @replaced_rhs << new_token
 
-            rule_builder = RuleBuilder.new(@rule_counter, @midrule_action_counter, i, lhs_tag: lhs_tag, skip_preprocess_references: true)
+            rule_builder = RuleBuilder.new(@rule_counter, @midrule_action_counter, i, lhs_tag: tag, skip_preprocess_references: true)
             rule_builder.lhs = new_token
             rule_builder.user_code = token
             rule_builder.complete_input

lib/lrama/lexer/token/user_code.rb

@@ -4,6 +4,8 @@ module Lrama
   class Lexer
     class Token
       class UserCode < Token
+        attr_accessor :tag
+
         def references
           @references ||= _references
         end

parser.y

@@ -462,10 +462,11 @@ rule
          {
            end_c_declaration
          }
-       "}" named_ref_opt
+       "}" named_ref_opt tag_opt
          {
            user_code = val[3]
            user_code.alias_name = val[6]
+           user_code.tag = val[7]
            builder = val[0]
            builder.user_code = user_code
            result = builder

sig/lrama/lexer/token/user_code.rbs

@@ -2,6 +2,7 @@ module Lrama
   class Lexer
     class Token
       class UserCode < Token
+        attr_accessor tag: Lexer::Token::Tag
         @references: Array[Lrama::Grammar::Reference]
 
         def references: () -> Array[Lrama::Grammar::Reference]