diff --git a/aoc.bqn b/aoc.bqn
index e33f8eb..e68f9a3 100644
--- a/aoc.bqn
+++ b/aoc.bqn
@@ -1,6 +1,6 @@
 Day1 ⇐ {
   nums ← •BQN⎊0¨ •FLines 𝕩
-  sums ← ∨ (+´ {𝕩↑𝕨↓nums}´)¨ (»⋈¨ ⊢-») / 0⊸≡¨ nums
+  sums ← ∨ (+´ {𝕩↑𝕨↓nums}´)¨ (»⋈¨ ⊢-») /0=nums
   ⟨⊑sums, +´ 3↑sums⟩
 }
 •Show Day1 ⊑•args
diff --git a/aoc.m b/aoc.m
index b419b07..3d84b57 100644
--- a/aoc.m
+++ b/aoc.m
@@ -9,32 +9,33 @@
 :- import_module string.
 :- import_module list.
 :- import_module exception.
+:- import_module univ.
 
 main(!IO) :- wrap_main(main2, !IO).
 
-:- pred main2(io::di, io::uo) is det.
+:- pred main2(io::di, io::uo) is cc_multi.
 main2(!IO) :-
   command_line_arguments(Args, !IO),
-  (if Args = [DayS, PartS | Rest],
+  (if Args = [DayS, PartS, File],
       to_int(DayS, Day),
-      part(PartS, Part) then
-    run(Day, Part, Rest, !IO)
-   else if Args = [D, P | _] then
-    die("expected a day and a part, got ""%s"" ""%s""", [s(D), s(P)])
-   else
-    die("expected at least two args")).
+      part(PartS, Part) then (
+    read_lines_need(File, Lines, !IO),
+    run_day(Day, Part, Lines, Out),
+    write_line(univ_value(Out), !IO)
+   ) else
+    die("expected day, part, filename")).
 
-:- type sol == (pred(part, list(string), io, io)).
-:- inst sol == (pred(in, in, di, uo) is det).
+:- type sol == (pred(part, list(string), univ)).
+:- inst sol == (pred(in, in, out) is cc_multi).
 
 :- pred solution(int::in, sol::out(sol)) is semidet.
 :- import_module day1.
 solution(1, day1.run).
 
-:- pred run(int::in, part::in, list(string)::in, io::di, io::uo) is det.
-
-run(Day, Part, Args, !IO) :-
+:- pred run_day(int, part, list(string), univ).
+:- mode run_day(in, in, in, out) is cc_multi.
+run_day(Day, Part, Lines, Out) :-
   if solution(Day, P) then
-    P(Part, Args, !IO)
+    P(Part, Lines, Out)
   else
     die("no solution for day %d", [i(Day)]).
diff --git a/basics.m b/basics.m
index 8229ec7..236595e 100644
--- a/basics.m
+++ b/basics.m
@@ -1,7 +1,7 @@
 :- module basics.
 :- interface.
-:- type part ---> one; two.
 
+:- type part ---> one; two.
 :- pred part(string, part).
 :- mode part(in,  out) is semidet.
 :- mode part(out, in)  is det.
@@ -18,10 +18,9 @@
 :- pred read_lines_need(string::in, list(string)::out, io::di, io::uo) is det.
 
 
-:- type main == (pred(io, io)).
-:- inst main == (pred(di, uo) is det).
-
-:- pred wrap_main(main::in(main), io::di, io::uo) is cc_multi.
+:- pred wrap_main(pred(io, io), io, io).
+:- mode wrap_main(pred(di, uo) is cc_multi, di, uo) is cc_multi.
+:- mode wrap_main(pred(di, uo) is det,      di, uo) is cc_multi.
 
 
 :- import_module maybe.
diff --git a/day1.m b/day1.m
index 73321e1..df3589d 100644
--- a/day1.m
+++ b/day1.m
@@ -1,10 +1,10 @@
 :- module day1.
 :- interface.
 :- import_module basics.
-:- import_module io.
 :- import_module list.
+:- import_module univ.
 
-:- pred run(part::in, list(string)::in, io::di, io::uo) is det.
+:- pred run(part::in, list(string)::in, univ::out) is cc_multi.
 
 :- implementation.
 :- import_module std_util.
@@ -12,17 +12,9 @@
 :- import_module string.
 :- import_module int.
 
-run(Part, Args, !IO) :-
-  if Args = [File] then (
-    read_lines_need(File, Lines, !IO),
-    Totals = go(Lines),
-    ( Part = one,
-        format("%d\n", [i(det_head(Totals))], !IO)
-    ; Part = two,
-        Res = sum(take_upto(3, Totals)),
-        format("%d\n", [i(Res)], !IO)
-    )
-  ) else die("expected one readable file").
+:- pragma no_determinism_warning(run/3).
+run(one, Lines, univ(det_head(go(Lines)))).
+run(two, Lines, univ(sum(take_upto(3, go(Lines))))).
 
 :- func go(list(string)) = list(int).
 go(Lines) =