Add function to merge clauses

resolution.py

@@ -1,6 +1,8 @@
 from emis_funky_funktions import *
 
-from ir import IRNeg, IRProp, IRTerm, IRVar, Substitutions, unify, unify_clauses
+from itertools import product
+
+from ir import Clause, IRNeg, IRProp, IRTerm, IRVar, Substitutions, sub_all, unify, unify_clauses
 
 def terms_cancel(t1: IRTerm, t2: IRTerm) -> Option[Substitutions]:
 	"""
@@ -27,6 +29,52 @@ def terms_cancel(t1: IRTerm, t2: IRTerm) -> Option[Substitutions]:
 			return hush(unify(x, IRNeg(a)))
 	return None
 
+def merge_clauses(c1: Clause, c2: Clause) -> Sequence[Clause]:
+    """
+    Produce a list of all possible clauses which resolution could derive from c1 and c2
+
+    For each term in c1 that could cancel with a term in c2 using a substitution, a
+    possible clause is produced equal to the concatenation of c1 and c2 with the canceled
+    terms removed and the substitution applied.
+
+    >>> merge_clauses(
+    ...     [ IRProp('day'), IRNeg(IRProp('night')) ],
+    ...     [ IRProp('night') ]
+    ... )
+    [[day()]]
+
+    >>> merge_clauses(
+    ...     [ IRNeg(IRProp('transgender', [IRVar('x1')])), IRProp('powerful', [IRVar('x1')]) ],
+    ...     [ IRNeg(IRProp('powerful', [IRVar('x2')])), IRProp('god', [IRVar('x2')]) ]
+    ... )
+    [[¬transgender(*x1), god(*x1)]]
+
+    >>> merge_clauses(
+    ...     [ IRNeg(IRProp('day')), IRProp('night') ],
+    ...     [ IRVar('x2') ]
+    ... )
+    [[night()], [¬day()]]
+
+    If two clauses cannot merge, an empty list is returned
+
+    >>> merge_clauses(
+    ...     [ IRProp('day') ],
+    ...     [ IRProp('wet') ]
+    ... )
+    []
+    """
+    valid_substitutions = drop_none(
+        map_opt(lambda subs: (subs, i1, i2), terms_cancel(t1, t2))
+        for ((i1, t1), (i2, t2)) in product(enumerate(c1), enumerate(c2))
+    )
+    return [
+        [
+            sub_all(subs, term)
+            for term in (*c1[:i1], *c1[i1 + 1:], *c2[:i2], *c2[i2 + 1:])
+        ]
+        for (subs, i1, i2) in valid_substitutions
+    ]
+
 if __name__ == '__main__':
 	import doctest
 	doctest.testmod()