Re: [bug-gawk] use of ;; as terminator, request for grammar help

[Richard Hansen]

On 2014-04-03 12:18, Eric Blake wrote:
> 2. Based on existing implementations, there is consensus that the POSIX
> grammar is overly restrictive, and that we should change it to permit:
>     awk '{print} {print}'
> and:
>     awk '/foo/; {print}'
> 
> since existing implementations all support it.  But to do that, we need
> someone with help in writing grammars to propose the changes to the one
> appearing on the POSIX page.  Any input would be appreciated.

Attached are two files:
  * awk-posix.y:  the current POSIX awk grammar (Issue 7 2013 Edition)
  * awk-proposed.y:  my attempt at modifying the grammar to accept the
    above examples and to reject actionless BEGIN and END patterns (to
    match the normative text)

For convenience you will find a unified diff of the two files below.

I am not an expert in either awk or yacc, so reviews would be appreciated.

Thanks,
Richard


diff --git a/awk.y b/awk.y
index b12ecd9..21f7357 100644
--- a/awk.y
+++ b/awk.y
@@ -49,23 +49,18 @@


 program          : item_list
-                 | actionless_item_list
+                 | item_list actionless_item
                  ;


-item_list        : newline_opt
-                 | actionless_item_list item terminator
-                 | item_list            item terminator
-                 | item_list          action terminator
+item_list        :                           terminator_opt
+                 | item_list item            terminator_opt
+                 | item_list actionless_item terminator
                  ;


-actionless_item_list : item_list            pattern terminator
-                 | actionless_item_list pattern terminator
-                 ;
-
-
-item             : pattern action
+item             : action
+                 | pattern action
                  | Function NAME      '(' param_list_opt ')'
                        newline_opt action
                  | Function FUNC_NAME '(' param_list_opt ')'
@@ -73,6 +68,10 @@ item             : pattern action
                  ;


+actionless_item  : normal_pattern
+                 ;
+
+
 param_list_opt   : /* empty */
                  | param_list
                  ;
@@ -83,13 +82,20 @@ param_list       : NAME
                  ;


-pattern          : Begin
-                 | End
-                 | expr
+pattern          : normal_pattern
+                 | special_pattern
+                 ;
+
+normal_pattern   : expr
                  | expr ',' newline_opt expr
                  ;


+special_pattern  : Begin
+                 | End
+                 ;
+
+
 action           : '{' newline_opt                             '}'
                  | '{' newline_opt terminated_statement_list   '}'
                  | '{' newline_opt unterminated_statement_list '}'
@@ -103,6 +109,11 @@ terminator       : terminator ';'
                  ;


+terminator_opt   : /* empty */
+                 | terminator
+                 ;
+
+
 terminated_statement_list : terminated_statement
                  | terminated_statement_list terminated_statement
                  ;

awk-posix.y
Description: Text document

awk-proposed.y
Description: Text document