Hi,

At Wed, 4 Feb 2004 09:21:49 +0900,
Jamis Buck wrote:
> What if we just use the keyword 'in' to introduce a flipflop, and retain 
> the range-ish syntax to separate the conditions?  Something like this:
> 
>   if in l=~/BEGIN/ .. l=~/END/
>      ...
>   end
> 
> The advantage of using a boolean phrase is that you can use it in 
> conditions, where it is most common.  That also lets you do something 
> when the flipflop is false, which the 'from..do' construct you suggested 
> doesn't (easily) allow.

Agreed, and it seems easy to implement.

> Since getting at the object that encapsulates the state of the flipflop 
> will be less common (one might even say "rare", although its hard to say 
> at this point since neither Perl nor Ruby allow it), the common case 
> (just getting the boolean result) should be simple and straightforward.  
> Getting at the object might be done via something like this:
> 
>   in l=~/BEGIN/ .. l=~/END/ => state
> 
> The expression itself still returns boolean, but the object 
> encapsulating the flipflop is placed in 'state'.

How will you use it, in other words, how and when it will be
changed?


Index: node.h
===================================================================
RCS file: /cvs/ruby/src/ruby/node.h,v
retrieving revision 1.52
diff -u -2 -p -d -r1.52 node.h
--- node.h	22 Jan 2004 08:31:33 -0000	1.52
+++ node.h	4 Feb 2004 00:53:13 -0000
@@ -327,4 +327,6 @@ typedef struct RNode {
 #define NEW_DOT2(b,e) NEW_NODE(NODE_DOT2,b,e,0)
 #define NEW_DOT3(b,e) NEW_NODE(NODE_DOT3,b,e,0)
+#define NEW_FLIP2(b,e) NEW_NODE(NODE_FLIP2,b,e,local_append(internal_id()))
+#define NEW_FLIP3(b,e) NEW_NODE(NODE_FLIP3,b,e,local_append(internal_id()))
 #define NEW_ATTRSET(a) NEW_NODE(NODE_ATTRSET,a,0,0)
 #define NEW_SELF() NEW_NODE(NODE_SELF,0,0,0)
Index: parse.y
===================================================================
RCS file: /cvs/ruby/src/ruby/parse.y,v
retrieving revision 1.315
diff -u -2 -p -d -r1.315 parse.y
--- parse.y	3 Feb 2004 02:23:20 -0000	1.315
+++ parse.y	4 Feb 2004 00:53:13 -0000
@@ -619,4 +619,12 @@ expr		: command_call
 			$$ = NEW_NOT(cond($2));
 		    }
+		| kIN arg tDOT2 arg
+		    {
+			$$ = NEW_FLIP2($2, $4);
+		    }
+		| kIN arg tDOT3 arg
+		    {
+			$$ = NEW_FLIP3($2, $4);
+		    }
 		| arg
 		;


-- 
Nobu Nakada