[developers] behaviour of read-lnk with <>

[Ann Copestake]

The version of read-lnk currently in the LKB trunk (in mrs/lnk.lisp) sometimes 
causes an error by swallowing too many characters when there's a empty link in 
an MRS (example below).  The error is a complaint about #\l being expected and 
not found because the read-mrs code is looking for LBL after calling read-lnk. 
 Apparently not all cases of <> trigger the problem but in a set of wescience 
treebank output files originally obtained from Dan, there were 4 cases which 
did throw an error.

I am uncertain under what circumstances empty links are allowed - if the 
intention is that they are invalid (under this sort of circumstance) then the 
mrs output code should presumably also be fixed to avoid producing them.

I have a feeling a related problem was mentioned somewhere recently, but I 
can't find it in the list - so sorry if this has been covered elsewhere.

Ann

[ LTOP: h1 INDEX: e2 [ e SF: PROP ] RELS: < [ implicit_conj_rel<1:28> LBL: h3 
ARG0: e2 L-HNDL: h4 L-INDEX: e7 [ e SF: PROP TENSE: PRES MOOD: INDICATIVE 
PROG: - PERF: - ] R-HNDL: h5 R-INDEX: e6 [ e SF: PROP TENSE: TENSED MOOD: 
INDICATIVE PROG: - PERF: - ] ] [ pron_rel<1:4> LBL: h8 ARG0: x9 [ x PERS: 2 
PRONTYPE: STD_PRON ] ] [ pronoun_q_rel<1:4> LBL: h10 ARG0: x9 RSTR: h11 BODY: 
h12 ] [ "_welcome_a_1_rel"<8:16> LBL: h13 ARG0: e7 ARG1: x9 ] [ 
_colon_v_id_rel<16:17> LBL: h14 ARG0: e6 ARG1: i15 ARG2: i16 [ i PERS: 3 NUM: 
SG ] ] [ udef_q_rel<16:17> LBL: h17 ARG0: i18 RSTR: h19 BODY: h20 ] [ 
"_go_v_1_rel"<18:28> LBL: h21 ARG0: e22 [ e SF: PROP TENSE: UNTENSED MOOD: 
INDICATIVE PROG: - PERF: - ] ARG1: i23 ] [ "_pre-_a_ante_rel"<18:28> LBL: h21 
ARG0: i24 ARG1: e22 ] [ fw_seq_rel<> LBL: h21 ARG0: i16 L-INDEX: e22 R-INDEX: 
i25 ] > HCONS: < h4 qeq h13 h5 qeq h14 h11 qeq h8 h19 qeq h26 > ]