fix(grammar): Correct ambiguities and restructure expression parsing

Signed-off-by: erick-alcachofa <erick@artichoke.dev>

The grammar contained several structural issues and ambiguities,
particularly in expression parsing, operator precedence, and the
`export` keyword. This commit restructures significant parts of the
grammar to resolve these problems and improve its formal correctness,
making it more suitable for parser generation.

The most relevant changes include:

* **Centralized Export Handling:** Corrects the definition of exports by
  introducing a top-level `<declaration>` rule that distinguishes
  between `<exportable_declaration>` and `<non_exportable_declaration>`.
  This removes the repetitive and ambiguous `export?` prefix from
  multiple individual declarations (`module`, `struct`, `fn`, etc.).

* **Unified Postfix Operations:** Integrates scoped access into the
  suffix operations . This provides an unambiguous and unified
  definition for these common constructs.

* **Updated Identifier Chain Issue:** Several rules in the precedence
  chain ultimately resolved into starting with an identifier, this
  caused ambiguitiy and issues for parsing, this was refactored in order
  to correctly handle the cases.

* **Reduced Ambiguity in Statements:** Refactors complex rules like
  `<variable_declaration>` and `<else_statement>` into smaller, more
  explicit sub-rules (`<variable_declaration_tail>`,
  `<else_statement_tail>`). This eliminates potential parsing conflicts
  and improves the overall clarity of the grammar.

* **Simplified Access Expressions:** Removes the separate
  `<scoped_access_expression>` and `<reflection_expression>` rules.
  Their logic has been integrated directly into the more generic and
  powerful postfix expression system, simplifying the grammar.

docs/grammar.ebnf

@@ -11,16 +11,29 @@
 /* A program is a sequence of top-level declarations and statements. */
 
 <program> =
-  ( <import_statement>
-  | <module_statement>
-  | <alias_statement>
-  | <struct_declaration>
-  | <enum_declaration>
-  | <function_declaration> )*
+  <declaration>*
   <eof>
 
+<declaration> =
+    "export" <exportable_declaration>
+  | <non_exportable_declaration>
+
+<exportable_declaration> =
+    <module_statement>
+  | <struct_declaration>
+  | <enum_declaration>
+  | <function_declaration>
+
+non_exportable_declaration =
+    <import_statement>
+  | <alias_statement>
+  | <module_statement>
+  | <struct_declaration>
+  | <enum_declaration>
+  | <function_declaration>
+
 <module_statement> =
-  "export"? "module" <namespaced_identifier> "{"
+  "module" <namespaced_identifier> "{"
     ( <module_statement>
     | <alias_statement>
     | <struct_declaration>
@@ -42,7 +55,7 @@
 /* Rules for defining functions, structs, enums, and their components. */
 
 <function_declaration> =
-  "export"? "fn" <identifier> <generic_params>? "(" <fn_params_list>? ")" ( "->" <type> )? <code_block>
+  "fn" <identifier> <generic_params>? "(" <fn_params_list>? ")" ( "->" <type> )? <code_block>
 
 <fn_params_list> =
     "this" <type> ("," <fn_param> ( "," <fn_param> )* )?
@@ -52,7 +65,7 @@
   <identifier> ":" <type>
 
 <struct_declaration> =
-  "export"? "struct" <identifier> <generic_params>? "{" <struct_members> "}"
+  "struct" <identifier> <generic_params>? "{" <struct_members> "}"
 
 <struct_members> =
   <struct_member> ( "," <struct_member> )*
@@ -61,7 +74,7 @@
   <identifier> ":" <type>
 
 <enum_declaration> =
-  "export"? "enum" <identifier> <generic_params>? "{" <enum_members> "}"
+  "enum" <identifier> <generic_params>? "{" <enum_members> "}"
 
 <enum_members> =
   <enum_member> ( "," <enum_member> )*
@@ -88,20 +101,23 @@
 <statement> =
     <variable_declaration> ";"
   | <if_statement>
-  | <loop_statement>
   | <defer_statement> ";"
   | <errdefer_statement> ";"
   | <return_statement> ";"
   | <break_statement> ";"
   | <continue_statement> ";"
-  | <expression> ";"
   | <alias_statement>
   | <match_statement>
   | <switch_statement>
+  | <loop_statement>
+  | <expression> ";"
 
 <variable_declaration> =
-    <variable_declarator> <identifier> ( ":" <type> )? "=" <expression>
-  | <variable_declarator> <identifier> ":" <type> ( "=" <expression> )?
+    <variable_declarator> <identifier> <variable_declaration_tail>
+
+<variable_declaration_tail> =
+    ":" <type> ( "=" <expression> )?
+  | "=" <expression>
 
 <variable_declarator> =
     "let"
@@ -112,8 +128,11 @@
   <else_statement>?
 
 <else_statement> =
-    "else" <variable_unwrapper>? <code_block>
-  | "else" <if_statement>
+    "else" <else_statement_tail>
+
+<else_statement_tail> =
+    <if_statement>
+  | <variable_unwrapper>? <code_block>
 
 <variable_unwrapper> =
   "|" <identifier> "|"
@@ -152,7 +171,7 @@
   "switch" "(" <expression> ")" "{" <switch_case>* <default_case>? "}"
 
 <match_case> =
-  ( <type_name> | <scoped_access_expression> ) ( "(" <identifier> ")" )? "->" <code_block>
+  <type_name> ( "(" <identifier> ")" )? "->" <code_block>
 
 <switch_case> =
   <expression> "->" <code_block>
@@ -204,45 +223,41 @@
   <prefix_expression> ( <multiply_op> <prefix_expression> )*
 
 <prefix_expression> =
-  <prefix_op>* <primary_expression>
+  <prefix_op>* <postfix_expression>
 
-<primary_expression> =
-  <primary_type_expression> ( <suffix_op> | <fn_call_arguments> )*
+<postfix_expression> =
+  <primary_expression> ( <suffix_op> | <fn_call_arguments> )*
 
 
 /* --- Primary Expressions & Literals --- */
 /* The highest-precedence expressions, including literals and grouped expressions. */
 
-<primary_type_expression> =
+<primary_expression> =
     <grouped_expression>
-  | <scoped_access_expression>
-  | <reflection_expression>
-  | <struct_literal>
-  | <type_name>
-  | <char_literal>
+  | <literal>
+  | <access_expression> ( "{" <struct_literal_body> "}" )?
+
+<access_expression> =
+  <identifier> ( "<" <types_list> ">" )?
+
+<literal> =
+    <char_literal>
   | <null_literal>
   | <string_literal>
   | <number_literal>
   | <boolean_literal>
-  | <identifier>
 
 <grouped_expression> =
   "(" <expression> ")"
 
-<scoped_access_expression> =
-  <type_name> "::" <identifier>
-
-<reflection_expression> =
-  ( <type_name> | <scoped_access_expression> ) ".@" <identifier>?
-
 <fn_call_arguments> =
   "(" <expression_list> ")"
 
 <expression_list> =
   (<expression> ",")* <expression>?
 
-<struct_literal> =
-  <type> "{" ( <named_field_list> | <positional_field_list> )? ","? "}"
+<struct_literal_body> =
+  ( <named_field_list> | <positional_field_list> )? ","?
 
 <named_field_list> =
   <named_field_init> ( "," <named_field_init> )*
@@ -278,15 +293,23 @@
 <prefix_op> = "!" | "-" | "~" | "&" | "*"
 
 <suffix_op> =
-    "[" <expression>? ":" <expression>? "]"
-  | "[" <expression> "]"
+    "[" <array_access_tail>
   | "." <identifier>
+  | "::" <identifier> ( "<" <types_list> ">" )?
   | "->" <identifier>
   | ".@" <identifier>?
   | ".[" <expression> "]"
   | ".#"
   | ".*"
 
+<array_access_tail> =
+    <expression> <slice_or_index_tail>
+  | ":" <expression>? "]"
+
+<slice_or_index_tail> =
+    "]"
+  | ":" <expression>? "]"
+
 /* --- Type System --- */
 /* Rules for defining types, type names, and type qualifiers. */
 
@@ -307,11 +330,10 @@
   | "?" <type_qualifier_chain_after_optional>?
 
 <type_name> =
-  <namespaced_identifier> ( "<" <types_list> ">" )?
+  <access_expression> ( "::" <identifier> ( "<" <types_list> ">" )? )*
 
 <namespaced_identifier> =
-    <identifier>
-  | <identifier> "::" <namespaced_identifier>
+    <identifier> ( "::" identifier )*
 
 <types_list> =
   <type> ( "," <types_list> )*