Start sketching out Split transition implementation

spacy/syntax/arc_eager.pyx

@@ -35,6 +35,8 @@ cdef enum:
 
     BREAK
 
+    SPLIT
+
     N_MOVES
 
 
@@ -44,6 +46,7 @@ MOVE_NAMES[REDUCE] = 'D'
 MOVE_NAMES[LEFT] = 'L'
 MOVE_NAMES[RIGHT] = 'R'
 MOVE_NAMES[BREAK] = 'B'
+MOVE_NAMES[SPLIT] = 'P'
 
 
 # Helper functions for the arc-eager oracle
@@ -60,6 +63,10 @@ cdef weight_t push_cost(StateClass stcls, const GoldParseC* gold, int target) no
         if BINARY_COSTS and cost >= 1:
             return cost
     cost += Break.is_valid(stcls.c, 0) and Break.move_cost(stcls, gold) == 0
+    # If the token wasn't split before, but gold says it *should* be split,
+    # don't push (split instead)
+    if USE_SPLIT and not stcls.c.was_split[stcls.c.B(0)]:
+        cost += gold.fused[stcls.c.B(0)]
     return cost
 
 
@@ -112,6 +119,7 @@ cdef bint label_is_gold(const GoldParseC* gold, int head, int child, attr_t labe
 cdef bint _is_gold_root(const GoldParseC* gold, int word) nogil:
     return gold.heads[word] == word or not gold.has_dep[word]
 
+
 cdef class Shift:
     @staticmethod
     cdef bint is_valid(const StateC* st, attr_t label) nogil:
@@ -124,8 +132,6 @@ cdef class Shift:
 
     @staticmethod
     cdef int transition(StateC* st, attr_t label) nogil:
-        #if label != 0:
-        #    st.split(st.B(1), label)
         st.shifted[st.B(0)] = 1
         st.push()
 
@@ -140,10 +146,41 @@ cdef class Shift:
     @staticmethod
     cdef inline weight_t label_cost(StateClass s, const GoldParseC* gold, attr_t label) nogil:
         return 0
-        #if gold.fused_tokens[s.B(1)] == label: TODO
-        #    return 0
-        #else:
-        #    return 1
+
+
+cdef class Split:
+    @staticmethod
+    cdef bint is_valid(const StateC* st, attr_t label) nogil:
+        if not USE_SPLIT:
+            return 0
+        elif st.buffer_length == 0:
+            return 0
+        elif st.is_split[st.B(0)]:
+            return 0
+        else:
+            return 1
+
+    @staticmethod
+    cdef int transition(StateC* st, attr_t label) nogil:
+        st.split(0, label)
+
+    @staticmethod
+    cdef weight_t cost(StateClass st, const GoldParseC* gold, attr_t label) nogil:
+        return Split.move_cost(st, gold) + Split.label_cost(st, gold, label)
+
+    @staticmethod
+    cdef weight_t move_cost(StateClass st, const GoldParseC* gold) nogil:
+        if gold.fused[st.B(0)]:
+            return 0
+        else:
+            return 1
+
+    @staticmethod
+    cdef weight_t label_cost(StateClass st, const GoldParseC* gold, attr_t label) nogil:
+        if gold.fused[st.B(0)] == label:
+            return 0
+        else:
+            return 1
 
 
 cdef class Reduce:
@@ -247,7 +284,11 @@ cdef class RightArc:
 
     @staticmethod
     cdef inline weight_t move_cost(StateClass s, const GoldParseC* gold) nogil:
-        if arc_is_gold(gold, s.S(0), s.B(0)):
+        # If the token wasn't split before, but gold says it *should* be split,
+        # don't right-arc (split instead)
+        if not s.c.was_split[s.c.B(0)] and gold.fused[s.c.B(0)]:
+            return gold.fused[s.c.B(0)]
+        elif arc_is_gold(gold, s.S(0), s.B(0)):
             return 0
         elif s.c.shifted[s.B(0)]:
             return push_cost(s, gold, s.B(0))
@@ -374,7 +415,7 @@ cdef class ArcEager(TransitionSystem):
 
     property action_types:
         def __get__(self):
-            return (SHIFT, REDUCE, LEFT, RIGHT, BREAK)
+            return (SHIFT, REDUCE, LEFT, RIGHT, BREAK, SPLIT)
 
     def get_cost(self, StateClass state, GoldParse gold, action):
         cdef Transition t = self.lookup_transition(action)
@@ -513,6 +554,10 @@ cdef class ArcEager(TransitionSystem):
             t.is_valid = Break.is_valid
             t.do = Break.transition
             t.get_cost = Break.cost
+        elif move == SPLIT:
+            t.is_valid = Split.is_valid
+            t.do = Split.transition
+            t.get_cost = Split.cost
         else:
             raise Exception(move)
         return t
@@ -543,6 +588,7 @@ cdef class ArcEager(TransitionSystem):
         is_valid[LEFT] = LeftArc.is_valid(st, 0)
         is_valid[RIGHT] = RightArc.is_valid(st, 0)
         is_valid[BREAK] = Break.is_valid(st, 0)
+        is_valid[SPLIT] = Split.is_valid(st, 0)
         cdef int i
         for i in range(self.n_moves):
             output[i] = is_valid[self.c[i].move]
@@ -561,12 +607,14 @@ cdef class ArcEager(TransitionSystem):
         move_cost_funcs[LEFT] = LeftArc.move_cost
         move_cost_funcs[RIGHT] = RightArc.move_cost
         move_cost_funcs[BREAK] = Break.move_cost
+        move_cost_funcs[SPLIT] = Split.move_cost
 
         label_cost_funcs[SHIFT] = Shift.label_cost
         label_cost_funcs[REDUCE] = Reduce.label_cost
         label_cost_funcs[LEFT] = LeftArc.label_cost
         label_cost_funcs[RIGHT] = RightArc.label_cost
         label_cost_funcs[BREAK] = Break.label_cost
+        label_cost_funcs[SPLIT] = Split.label_cost
 
         cdef attr_t* labels = gold.c.labels
         cdef int* heads = gold.c.heads