Custom syntax for floating attributes: [@@@id].

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14588 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

experimental/frisch/extension_points.txt

@@ -78,10 +78,11 @@ Attributes on items:
     let x1 = ... [@@id1] [@@id2] and x2 = ... [@@id3] [@@id4]
 
 
-  The [@@id s] form, when used at the beginning of a signature or
-  structure, or after a double semi-colon (;;), defines an attribute
-  which stands as a stand-alone signature or structure item (not
-  attached to another item).
+Floating attributes:
+
+  The [@@@id s] form defines an attribute which stands as a
+  stand-alone signature or structure item (not attached to another
+  item).
 
   Example:
 
@@ -89,13 +90,13 @@ Attributes on items:
     [@@id1]
     type t
     [@@id2]
-    ;; [@@id3] [@@id4]
-    ;; [@@id5]
+    [@@@id3] [@@@id4]
+    [@@@id5]
     type s
     [@@id6]
   end
 
-  Here, id1, id3, id4, id5 are stand-alone attributes, while
+  Here, id1, id3, id4, id5 are floating attributes, while
   id2 is attached to the type t and id6 is attached to the type s.
 
 === Extension nodes
@@ -249,9 +250,21 @@ to represent attributes.
 It is now possible to start a signature or a structure with a ";;" token and to have two successive ";;" tokens.
 
 Rationale:
-   It makes it possible to always prefix a "standalone" attribute by ";;" independently
-   from its context (this will work at the beginning of the signature/structure and after
-   another item finished with ";;").
+   In an intermediate version of this branch, floating attributes shared
+   the same syntax as item attributes, with the constraints that they
+   had to appear either at the beginning of their structure or signature,
+   or after ";;".  The relaxation above made is possible to always prefix
+   a floating attributes by ";;" independently of its context.
+
+   Floating attributes now have a custom syntax [@@@id], but this changes
+   is harmless, and the same argument holds for toplevel expressions:
+   it is always possile to write:
+
+     ;; print_endline "bla";;
+
+   without having to care about whether the previous structure item
+   ends with ";;" or not.
+
 
 -- Relaxing the syntax for exception declarations
 

parsing/lexer.mll

@@ -446,6 +446,7 @@ rule token = parse
   | "[%" { LBRACKETPERCENT }
   | "[%%" { LBRACKETPERCENTPERCENT }
   | "[@@" { LBRACKETATAT }
+  | "[@@@" { LBRACKETATATAT }
   | "!"  { BANG }
   | "!=" { INFIXOP0 "!=" }
   | "+"  { PLUS }

parsing/parser.mly

@@ -354,6 +354,7 @@ let mkexp_attrs d attrs =
 %token LPAREN
 %token LBRACKETAT
 %token LBRACKETATAT
+%token LBRACKETATATAT
 %token MATCH
 %token METHOD
 %token MINUS
@@ -500,8 +501,7 @@ toplevel_phrase:
   | EOF                                  { raise End_of_file }
 ;
 top_structure:
-    str_attribute top_structure   { $1 :: $2 }
-  | seq_expr post_item_attributes { [mkstrexp $1 $2] }
+    seq_expr post_item_attributes { [mkstrexp $1 $2] }
   | top_structure_tail            { $1 }
 ;
 top_structure_tail:
@@ -603,8 +603,7 @@ module_expr:
 ;
 
 structure:
-    str_attribute structure { $1 :: $2 }
-  | seq_expr post_item_attributes structure_tail { mkstrexp $1 $2 :: $3 }
+    seq_expr post_item_attributes structure_tail { mkstrexp $1 $2 :: $3 }
   | structure_tail { $1 }
 ;
 structure_tail:
@@ -612,9 +611,6 @@ structure_tail:
   | SEMISEMI structure   { $2 }
   | structure_item structure_tail { $1 :: $2 }
 ;
-str_attribute:
-    post_item_attribute { mkstr(Pstr_attribute $1) }
-;
 structure_item:
     LET ext_attributes rec_flag let_bindings
       {
@@ -661,6 +657,8 @@ structure_item:
       { mkstr(Pstr_include ($2, $3)) }
   | item_extension post_item_attributes
       { mkstr(Pstr_extension ($1, $2)) }
+  | floating_attribute
+      { mkstr(Pstr_attribute $1) }
 ;
 module_binding_body:
     EQUAL module_expr
@@ -708,16 +706,9 @@ module_type:
       { Mty.attr $1 $2 }
 ;
 signature:
-    sig_attribute signature { $1 :: $2 }
-  | signature_tail { $1 }
-;
-signature_tail:
     /* empty */          { [] }
   | SEMISEMI signature   { $2 }
-  | signature_item signature_tail { $1 :: $2 }
-;
-sig_attribute:
-    post_item_attribute { mksig(Psig_attribute $1) }
+  | signature_item signature { $1 :: $2 }
 ;
 signature_item:
     VAL val_ident COLON core_type post_item_attributes
@@ -760,6 +751,8 @@ signature_item:
       { mksig(Psig_class_type (List.rev $3)) }
   | item_extension post_item_attributes
       { mksig(Psig_extension ($1, $2)) }
+  | floating_attribute
+      { mksig(Psig_attribute $1) }
 ;
 
 module_declaration:
@@ -2069,6 +2062,9 @@ attribute:
 post_item_attribute:
   LBRACKETATAT attr_id payload RBRACKET { ($2, $3) }
 ;
+floating_attribute:
+  LBRACKETATATAT attr_id payload RBRACKET { ($2, $3) }
+;
 post_item_attributes:
     /* empty */  { [] }
   | post_item_attribute post_item_attributes { $1 :: $2 }