If statement generates two outputs

This is probably due to that in the gram.y file :

case ':':
   if (nextchar(':')) {
       if (nextchar(':')) {
       yylval = install(":::");
       return NS_GET_INT;
       }
       else {
       yylval = install("::");
       return NS_GET;
       }
   }
   if (nextchar('=')) {
       yylval = install(":=");
       return LEFT_ASSIGN;
   }
   yylval = install(":");
   return ':';
   which gives a meaning to ":=", so that parsing x := 2 makes sense.

parse( text = "x := 2" )

expression(x := 2)
attr(,"srcfile")
<text>

thanks.  so it seems to be intentionally parsable, though i wouldn't say
that this gives a meaning to ':=' -- the operator has a syntactic
category, but no semantics.  the syntactic category does not imply any
semantics, as in

    '<-' = function(a, b) NULL
    1 <- a
    # NULL

where '<-' is still parsed the original way (as a LEFT_ASSIGN, gram.y
again), but has now a completely different semantics.

it looks like a bug to me:  ':=' is parsed on par with '<-' as a
LEFT_ASSIGN, but apparently is not backed by any function.  it's a
zombie.  (unless rvalues is used, that is.)

vQ