BW BQL entry seems to have sticky parser errors

[Joseph Oswald]

$ bw --driver=VOLATILE bql
...
bql> CREATE GRAPH ?foo;
[OK]
bql> INSERT DATA INTO ?foo {
/u<joe> "parent_of"@[2016-12-12T15:00Z] /u<julia>
};
[ERROR] failed to parse BQL statement with error predicate.Parse failed to parse time anchor
2016-12-12T15:00Z in "parent_of"@[2016-12-12T15:00Z] with error parsing time 
"2016-12-12T15:00Z" as "2006-01-02T15:04:05.999999999Z07:00": cannot parse "Z" as ":"

bql> INSERT DATA INTO ?foo { /u<joe> "parent_of"@[] /u<julia> };
[ERROR] failed to parse BQL statement with error hook.DataAccumulator requires a predicate to
create a predicate, got &{NODE /u<joe> } instead

# This second error is spurious, but sticky. Only quitting and restarting bw seems to allow data to be
# inserted. If I enter the same sequence but with an acceptable timestamp, the second error does not
# occur.

bql> INSERT DATA INTO ?foo { /u<joe> "parent_of"@[] /u<fred> };
[ERROR] failed to parse BQL statement with error hook.DataAccumulator requires a predicate to create a predicate, got &{NODE /u<joe> } instead

bql> quit;
Thanks for all those BQL queries!

$ bw --driver=VOLATILE bql
Welcome to BadWolf vCli (0.5.1-dev @141940248)
Using driver "VOLATILE". Type quit; to exit
Session started at 2016-12-21 13:50:07.001652809 -0500 EST

bql> CREATE GRAPH ?foo;
[OK]
bql> INSERT DATA INTO ?foo {
/u<joe> "parent_of"@[2016-12-12T15:00:00Z] /u<julia>
};
[OK]
bql> INSERT DATA INTO ?foo { /u<joe> "parent_of"@[] /u<julia> };
[OK]
bql> INSERT DATA INTO ?foo { /u<joe> "parent_of"@[] /u<fred> };
[OK]

[Xavier Llorà]

Thanks @jaoswald for reporting. I have been looking at it and I found the issue. There semantic structures are not properly flushed between parser runs. Working on a fix.