Add unit test for missing lins

testsuite/lpgf/unittests/Missing.gf

@@ -0,0 +1,7 @@
+abstract Missing = {
+  cat S; NP; V2;
+  fun
+    Pred: NP -> V2 -> NP -> S;
+    John, Dogs, Fish: NP ;
+    Love, Eat: V2 ;
+}

testsuite/lpgf/unittests/Missing.treebank

@@ -0,0 +1,12 @@
+Missing: Pred John Love Fish
+MissingCnc: John loves fish a lot
+
+Missing: Pred John Eat Fish
+MissingCnc: John [Eat] fish [Eat]
+
+Missing: Pred Fish Love Dogs
+MissingCnc: fish love [Dogs] a lot
+
+Missing: Pred Dogs Eat Fish
+MissingCnc: [Dogs] [Eat] fish [Eat]
+

testsuite/lpgf/unittests/Missing.trees

@@ -0,0 +1,4 @@
+Pred John Love Fish
+Pred John Eat Fish
+Pred Fish Love Dogs
+Pred Dogs Eat Fish

testsuite/lpgf/unittests/MissingCnc.gf

@@ -0,0 +1,25 @@
+concrete MissingCnc of Missing = open Prelude, ParamX in {
+  lincat
+    S = SS ;
+    NP = { s : Str ; n : Number } ;
+    V2 = { s : Number => Str; s2 : Str } ;
+  lin
+    Pred subj verb obj = ss (subj.s ++ verb.s ! subj.n ++ obj.s ++ verb.s2) ;
+    John = { s = "John" ; n = Sg } ;
+    -- Dogs = { s = "dogs" ; n = Pl } ;
+    Fish = { s = "fish" ; n = Pl } ;
+    Love = {
+      s = table {
+        Sg => "loves" ;
+        Pl => "love"
+      } ;
+      s2 = "a lot"
+    } ;
+    -- Eat = {
+    --   s = table {
+    --     Sg => "eats" ;
+    --     Pl => "eat"
+    --   } ;
+    --   s2 = "often"
+    -- } ;
+}