ruby-core

I think I've found why this is happening. The trace hook for NODE_IF is
getting called a before the expression evaluation occurs when it should be
called afterwards. Attached is a patch. I will also update
#18722<http://rubyforge.org/tracker/index.php?func=detail&aid=18722&group_id=426&atid=22040>with
this information.

Thanks.

On Thu, Mar 13, 2008 at 2:32 PM, Rocky Bernstein <rocky.bernstein@gmail.com>
wrote:

> Thanks. The output you report matches what I get in 1.8.6 and suggests
> where to start looking for a bug. I'm not sure this is strictly related to
> blocks. In particular try this:
>
> x = 6.2*1 if
>   x=6.1
>
> The line break after the "if" is intentional since it more clearly shows
> which part gets run when. In this code,
> first there are two stops on the x=6.1 presumably before and after the
> assignment. But by the time of the c-call to multiply 6.2*1, the value of
> x is 6.1. It is like some sort of register flushing that is going before
> the c-call, but again that's pure guess.
>
> On Thu, Mar 13, 2008 at 12:59 PM, Yemi I. D. Bedu <yemi@weldfast.com>
> wrote:
>
> >  Hello,
> >
> >  I tried this and it has to do with implicit / explicit block. Also I
> > expanded example:
> >
> >
> >
> > p RUBY_VERSION
> >
> >
> >
> > def trace_func(event, file, line, id, binding, klass, *)
> >
> >   printf("%s:%d (%s) x=%s\n", file, line, event, eval("x", binding))
> >
> > end
> >
> >
> >
> > set_trace_func method(:trace_func).to_proc
> >
> >
> >
> > x=2
> >
> > (x=3.2) if x=3.1
> >
> > begin x=4.2 end if x=4.1
> >
> > x=5.2 if x=5.1
> >
> > x=6.2*1 if x=6.1*1
> >
> > if x=7.1 then x=7.2 end
> >
> > x=8
> >
> > x=9
> >
> >
> >
> > My Results were:
> >
> >
> >
> > "1.8.2"
> >
> >
> >
> > tt.rb:9 (line) x=
> >
> >
> >
> > tt.rb:10 (line) x=2
> >
> > tt.rb:10 (line) x=2
> >
> > tt.rb:10 (line) x=3.1
> >
> >
> >
> > tt.rb:11 (line) x=3.2
> >
> > tt.rb:11 (line) x=3.2
> >
> > tt.rb:11 (line) x=4.1
> >
> >
> >
> > tt.rb:12 (line) x=4.2
> >
> > tt.rb:12 (line) x=4.2
> >
> >
> >
> > tt.rb:13 (line) x=5.2
> >
> > tt.rb:13 (line) x=5.2
> >
> > tt.rb:13 (c-call) x=5.2
> >
> > tt.rb:13 (c-return) x=5.2
> >
> > tt.rb:13 (c-call) x=6.1
> >
> > tt.rb:13 (c-return) x=6.1
> >
> >
> >
> > tt.rb:14 (line) x=6.2
> >
> > tt.rb:14 (line) x=6.2
> >
> > tt.rb:14 (line) x=7.1
> >
> >
> >
> > tt.rb:15 (line) x=7.2
> >
> >
> >
> > tt.rb:16 (line) x=8
> >
> >
> >
> > You would need to either have parens, explicit block or use the other if
> > form to get that last firing from the trace. It seems to token out each
> > expression unit on a line and then call eval to get the previous lines
> > value. I don't know if you can confirm this on your 1.8.6 install. The
> > lines with the multiply do func calls so they eval before going into the new
> > env and when the come back. You might want to have a more complex expression
> > execute like a list comprehension or a map. Good day.
> >
> > Yemi Bedu
> >
> > P&R Fasteners, Inc.
> > P&R Castings, LLC.
> > 325 Pierce St
> > Somerset, NJ 08873
> > (T) 732-302-3600
> > (F) 732-302-3636
> >   ------------------------------
> >
> > *From:* Rocky Bernstein [mailto:rocky.bernstein@gmail.com]
> > *Sent:* Wednesday, March 12, 2008 11:21 PM
> > *To:* ruby-core@ruby-lang.org
> > *Subject:* Ruby 1.8.6 binding value after "if" expression evaluation
> >
> >
> >
> > Here's another trace hook weirdness that I've encountered.
> >
> > Consider this program and its output:
> >
> > def trace_func(event, file, line, id, binding, klass, *)
> >   printf("%s:%d (%s) x=%s\n", file, line, event, eval("x", binding))
> > end
> > set_trace_func method(:trace_func).to_proc
> > x=5
> > x=6.2 if x=6.1
> > x=7
> >
> >
> > $ ruby bug2.rb
> > bug2.rb:6: warning: found = in conditional, should be ==
> > bug2.rb:5 (line) x=
> > bug2.rb:6 (line) x=5
> > bug2.rb:6 (line) x=5
> > bug2.rb:7 (line) x=6.2
> >
> > Why does x appear to have value 5 the second time on line 7 rather than
> > 6.1?
> >
> > Looking at eval.c what's supposed to happen (I think) is that the trace
> > hook is called before the expression (x=6.1) is evaluated and then
> > called before the assignment "x=6.2" in which case it should have value
> > 6.1, not 5.
> >
> > Can anyone explain why this happens?
> >
> > Again this is ruby 1.8.6
> >
>
>

Attachments (1)

eval.c.diff (666 Bytes, text/x-diff)

Index: eval.c
===================================================================
--- eval.c	(revision 15769)
+++ eval.c	(working copy)
@@ -3038,13 +3038,16 @@
 	RETURN(Qfalse);
 
       case NODE_IF:
-	EXEC_EVENT_HOOK(RUBY_EVENT_LINE, node, self,
-			ruby_frame->last_func,
-			ruby_frame->last_class);
 	if (RTEST(rb_eval(self, node->nd_cond))) {
+	    EXEC_EVENT_HOOK(RUBY_EVENT_LINE, node, self,
+			    ruby_frame->last_func,
+			    ruby_frame->last_class);
 	    node = node->nd_body;
 	}
 	else {
+	    EXEC_EVENT_HOOK(RUBY_EVENT_LINE, node, self,
+			    ruby_frame->last_func,
+			    ruby_frame->last_class);
 	    node = node->nd_else;
 	}
 	goto again;

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