fix(grammar): Simplify and improve EBNF definition

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

The EBNF grammar definition contained several redundancies,
inconsistencies, and minor omissions. This commit refactors the grammar
to make it more concise, readable, and robust for parsing.

Key changes include:

- **Rule Simplification**: Redundant intermediate rules (`fn_params`,
  `statements`, `assign_expression`) have been removed. Rules like
  `code_block` and `import_target` are now more concisely expressed
  using standard EBNF operators (`?`, `*`).

- **EOF Enforcement**: The top-level `program` rule now requires an
  `<eof>` token. This is a crucial fix to ensure the parser consumes the
  entire file and fails on trailing invalid tokens.

- **Optional Generics**: Generic parameters (`<... >`) are now correctly
  marked as optional on `function`, `struct`, and `enum` declarations,
  which was the original intent.

- **Flexible For-Loops**: The update/increment expression (the third
  part) in a C-style `for` loop is now optional, aligning with behavior
  in languages like C and C++.

- **Primary Expressions**: Primary type expressions failed to parse
  correctly namespaced elements and types, now it's fixed and improved.

docs/grammar.ebnf

@@ -7,7 +7,6 @@
 ================================================================================
 */
 
-
 /* --- Program Structure --- */
 /* A program is a sequence of top-level declarations and statements. */
 
@@ -18,6 +17,7 @@
   | <struct_declaration>
   | <enum_declaration>
   | <function_declaration> )*
+  <eof>
 
 <module_statement> =
   "export"? "module" <namespaced_identifier> "{"
@@ -32,8 +32,7 @@
   "import" <import_target> ";"
 
 <import_target> =
-    <namespaced_identifier>
-  | <namespaced_identifier> "::" "*"
+    <namespaced_identifier> ( "::" "*" )?
 
 <alias_statement> =
   "using" <identifier> "=" <namespaced_identifier> ";"
@@ -43,10 +42,7 @@
 /* Rules for defining functions, structs, enums, and their components. */
 
 <function_declaration> =
-  "export"? "fn" <identifier> <generic_params> "(" <fn_params> ")" ( "->" <type> )? <code_block>
-
-<fn_params> =
-  <fn_params_list>?
+  "export"? "fn" <identifier> <generic_params>? "(" <fn_params_list>? ")" ( "->" <type> )? <code_block>
 
 <fn_params_list> =
     "this" <type> ("," <fn_param> ( "," <fn_param> )* )?
@@ -56,7 +52,7 @@
   <identifier> ":" <type>
 
 <struct_declaration> =
-  "export"? "struct" <identifier> <generic_params> "{" <struct_members> "}"
+  "export"? "struct" <identifier> <generic_params>? "{" <struct_members> "}"
 
 <struct_members> =
   <struct_member> ( "," <struct_member> )*
@@ -65,7 +61,7 @@
   <identifier> ":" <type>
 
 <enum_declaration> =
-  "export"? "enum" <identifier> <generic_params> "{" <enum_members> "}"
+  "export"? "enum" <identifier> <generic_params>? "{" <enum_members> "}"
 
 <enum_members> =
   <enum_member> ( "," <enum_member> )*
@@ -74,7 +70,7 @@
   <identifier> ( "(" <type> ")" )?
 
 <generic_params> =
-  ( "<" <generic_params_list> ">" )?
+  "<" <generic_params_list> ">"
 
 <generic_params_list> =
   <generic_param> ( "," <generic_param> )*
@@ -87,10 +83,7 @@
 /* Rules for code blocks, variable declarations, and control structures. */
 
 <code_block> =
-  "{" <statements>? "}"
-
-<statements> =
-  <statement> ( <statement> )*
+  "{" <statement>* "}"
 
 <statement> =
     <variable_declaration> ";"
@@ -101,7 +94,7 @@
   | <return_statement> ";"
   | <break_statement> ";"
   | <continue_statement> ";"
-  | <expression_statement>
+  | <expression> ";"
   | <alias_statement>
   | <match_statement>
   | <switch_statement>
@@ -135,7 +128,7 @@
   )
 
 <c_for_statement> =
-  "for" "(" <variable_declaration>? ";" <expression> ";" <expression> ")"
+  "for" "(" <variable_declaration>? ";" <expression> ";" <expression>? ")"
   <code_block>
 
 <range_for_statement> =
@@ -182,17 +175,11 @@
 <return_statement> =
   "return" <expression>?
 
-<expression_statement> =
-  <expression> ";"
-
 
 /* --- Expressions & Operator Precedence --- */
 /* The full expression hierarchy, from lowest to highest precedence. */
 
 <expression> =
-  <assign_expression>
-
-<assign_expression> =
   <bool_or_expression> ( ( <assign_op> | <compound_assign_op> ) <expression> )?
 
 <bool_or_expression> =
@@ -227,16 +214,17 @@
 /* The highest-precedence expressions, including literals and grouped expressions. */
 
 <primary_type_expression> =
-    <char_literal>
+    <grouped_expression>
+  | <scoped_access_expression>
+  | <reflection_expression>
+  | <struct_literal>
+  | <type_name>
+  | <char_literal>
   | <null_literal>
   | <string_literal>
   | <number_literal>
   | <boolean_literal>
-  | <grouped_expression>
   | <identifier>
-  | <struct_literal>
-  | <scoped_access_expression>
-  | <reflection_expression>
 
 <grouped_expression> =
   "(" <expression> ")"
@@ -245,7 +233,7 @@
   <type_name> "::" <identifier>
 
 <reflection_expression> =
-  ( <primary_expression> | <type_name> | <scoped_access_expression> ) ".@" <identifier>?
+  ( <type_name> | <scoped_access_expression> ) ".@" <identifier>?
 
 <fn_call_arguments> =
   "(" <expression_list> ")"
@@ -292,9 +280,10 @@
 <suffix_op> =
     "[" <expression>? ":" <expression>? "]"
   | "[" <expression> "]"
-  | ".[" <expression> "]"
   | "." <identifier>
   | "->" <identifier>
+  | ".@" <identifier>?
+  | ".[" <expression> "]"
   | ".#"
   | ".*"
 
@@ -302,7 +291,7 @@
 /* Rules for defining types, type names, and type qualifiers. */
 
 <type> =
-  <type_qualifier_chain> <type_name>
+  <type_qualifier_chain>? <type_name>
 
 <type_qualifier_chain> =
     ( "*" | "[]" ) <type_qualifier_chain>?
@@ -345,4 +334,4 @@
 <nonzero_digit> = [1-9]
 
 <empty> = E /* Represents an empty terminal string */
-
+<eof> = /* End Of File */