unwrap fate_to_erlang results

fate_to_erlang can only really fail at runtime if the wrong AACI is provided, in which case the details of how failure occured are not helpful, or recoverable. Anything else will be so broken that dialyzer will catch it, or is a bug in hakuzaru, that we want to know about.
Add special anonymous variant syntax
2026-06-08 07:23:34 +00:00 · 2026-06-05 03:08:38 +00:00 · 2026-05-28 00:41:51 +00:00
2 changed files with 308 additions and 214 deletions
@@ -527,10 +527,7 @@ opaque_type(Params, #{record := FieldDefs}) ->
              || #{name := Name, type := Type} <- FieldDefs],
    {record, Fields};
 opaque_type(Params, #{variant := VariantDefs}) ->
-    ConvertVariant = fun(Pair) ->
-        [{Name, Types}] = maps:to_list(Pair),
-        {binary_to_list(Name), [opaque_type(Params, Type) || Type <- Types]}
-    end,
+    ConvertVariant = fun(Pair) -> opaque_variant_each(Params, Pair) end,
    Variants = lists:map(ConvertVariant, VariantDefs),
    {variant, Variants};
 opaque_type(Params, #{tuple := TypeDefs}) ->
@@ -541,6 +538,11 @@ opaque_type(Params, Pair) when is_map(Pair) ->
    [{Name, TypeArgs}] = maps:to_list(Pair),
    {opaque_type_name(Name), [opaque_type(Params, Arg) || Arg <- TypeArgs]}.

+opaque_variant_each(Params, Pair) ->
+    [{Name, Types}] = maps:to_list(Pair),
+    ElemTypes = [opaque_type(Params, Type) || Type <- Types],
+    {binary_to_list(Name), ElemTypes}.
+

 -spec opaque_type_name(binary()) -> atom() | string().
 % Atoms for any builtins that aren't qualified by a namespace in Sophia.
@@ -848,7 +850,7 @@ erlang_args_to_fate(VarTypes, Terms) ->
    DefLength = length(VarTypes),
    ArgLength = length(Terms),
    if
-        DefLength =:= ArgLength -> coerce_zipped_bindings(lists:zip(VarTypes, Terms), to_fate, arg);
+        DefLength =:= ArgLength -> coerce_zipped_bindings(lists:zip(VarTypes, Terms), arg);
        DefLength >   ArgLength -> {error, too_few_args};
        DefLength   < ArgLength -> {error, too_many_args}
    end.
@@ -926,7 +928,10 @@ erlang_to_fate({O, N, char}, Str) ->
            single_error({invalid, O, N, Str})
    end;
 erlang_to_fate({O, N, {bytes, [Count]}}, Bytes) when is_bitstring(Bytes) ->
-    coerce_bytes(O, N, Count, Bytes);
+    case check_bytes(O, N, Count, Bytes) of
+        ok              -> {ok, {bytes, Bytes}};
+        {error, Reason} -> {error, Reason}
+    end;
 erlang_to_fate({_, _, bits}, Num) when is_integer(Num) ->
    {ok, {bits, Num}};
 erlang_to_fate({_, _, bits}, Bits) when is_bitstring(Bits) ->
@@ -934,19 +939,19 @@ erlang_to_fate({_, _, bits}, Bits) when is_bitstring(Bits) ->
    <<IntValue:Size>> = Bits,
    {ok, {bits, IntValue}};
 erlang_to_fate({_, _, {list, [Type]}}, Data) when is_list(Data) ->
-    coerce_list(Type, Data, to_fate);
+    coerce_list(Type, Data);
 erlang_to_fate({_, _, {map, [KeyType, ValType]}}, Data) when is_map(Data) ->
-    coerce_map(KeyType, ValType, Data, to_fate);
+    coerce_map(KeyType, ValType, Data);
 erlang_to_fate({O, N, {tuple, ElementTypes}}, Data) when is_tuple(Data) ->
    ElementList = tuple_to_list(Data),
-    coerce_tuple(O, N, ElementTypes, ElementList, to_fate);
+    coerce_tuple(O, N, ElementTypes, ElementList);
 erlang_to_fate({O, N, {variant, Variants}}, Name) when is_list(Name) ->
    erlang_to_fate({O, N, {variant, Variants}}, {Name});
 erlang_to_fate({O, N, {variant, Variants}}, Data) when is_tuple(Data), tuple_size(Data) > 0 ->
    [Name | Terms] = tuple_to_list(Data),
    case lookup_variant(Name, Variants) of
        {Tag, TermTypes} ->
-            coerce_variant2(O, N, Variants, Name, Tag, TermTypes, Terms, to_fate);
+            coerce_variant2(O, N, Variants, Name, Tag, TermTypes, Terms);
        not_found ->
            ValidNames = [Valid || {Valid, _} <- Variants],
            single_error({invalid_variant, O, N, Name, ValidNames})
@@ -954,17 +959,15 @@ erlang_to_fate({O, N, {variant, Variants}}, Data) when is_tuple(Data), tuple_siz
 erlang_to_fate({O, N, {record, MemberTypes}}, Map) when is_map(Map) ->
    coerce_map_to_record(O, N, MemberTypes, Map);
 erlang_to_fate({O, N, {unknown_type, _}}, Data) ->
-    case N of
-        already_normalized ->
-            Message = "Warning: Unknown type ~p. Using term ~p as is.~n",
-            io:format(Message, [O, Data]);
-        _ ->
-            Message = "Warning: Unknown type ~p (i.e. ~p). Using term ~p as is.~n",
-            io:format(Message, [O, N, Data])
-    end,
+    warn_unknown_type(O, N, Data),
    {ok, Data};
 erlang_to_fate({O, N, _}, Data) -> single_error({invalid, O, N, Data}).

+warn_unknown_type(O, already_normalized, Data) ->
+    io:format("Warning: Unknown type ~p. Using term ~p as is.~n", [O, Data]);
+warn_unknown_type(O, N, Data) ->
+    io:format("Warning: Unknown type ~p (i.e. ~p). Using term ~p as is.~n", [O, N, Data]).
+
 coerce_chain_object(_, _, _, _, {raw, Binary}) ->
    {ok, Binary};
 coerce_chain_object(O, N, T, Tag, S) ->
@@ -988,78 +991,78 @@ decode_chain_object(Tag, S) ->
        error:incorrect_size -> {error, incorrect_size}
    end.

-coerce_bytes(O, N, _, Bytes) when bit_size(Bytes) rem 8 /= 0 ->
+check_bytes(O, N, _, Bytes) when bit_size(Bytes) rem 8 /= 0 ->
    single_error({partial_bytes, O, N, bit_size(Bytes)});
-coerce_bytes(_, _, any, Bytes) ->
-    {ok, Bytes};
-coerce_bytes(O, N, Count, Bytes) when byte_size(Bytes) /= Count ->
+check_bytes(_, _, any, _) ->
+    ok;
+check_bytes(O, N, Count, Bytes) when byte_size(Bytes) /= Count ->
    single_error({incorrect_size, O, N, Bytes});
-coerce_bytes(_, _, _, Bytes) ->
-    {ok, Bytes}.
+check_bytes(_, _, _, _) ->
+    ok.

-coerce_zipped_bindings(Bindings, Direction, Tag) ->
-    coerce_zipped_bindings(Bindings, Direction, Tag, [], []).
+coerce_zipped_bindings(Bindings, Tag) ->
+    coerce_zipped_bindings(Bindings, Tag, [], []).

-coerce_zipped_bindings([Next | Rest], Direction, Tag, Good, Broken) ->
+coerce_zipped_bindings([Next | Rest], Tag, Good, Broken) ->
    {{ArgName, Type}, Term} = Next,
-    case coerce_direction(Type, Term, Direction) of
+    case erlang_to_fate(Type, Term) of
        {ok, NewTerm} ->
-            coerce_zipped_bindings(Rest, Direction, Tag, [NewTerm | Good], Broken);
+            coerce_zipped_bindings(Rest, Tag, [NewTerm | Good], Broken);
        {error, Errors} ->
            Wrapped = wrap_errors({Tag, ArgName}, Errors),
-            coerce_zipped_bindings(Rest, Direction, Tag, Good, [Wrapped | Broken])
+            coerce_zipped_bindings(Rest, Tag, Good, [Wrapped | Broken])
    end;
-coerce_zipped_bindings([], _, _, Good, []) ->
+coerce_zipped_bindings([], _, Good, []) ->
    {ok, lists:reverse(Good)};
-coerce_zipped_bindings([], _, _, _, Broken) ->
+coerce_zipped_bindings([], _, _, Broken) ->
    {error, combine_errors(Broken)}.

-coerce_list(Type, Elements, Direction) ->
+coerce_list(Type, Elements) ->
    % 0 index since it represents a sophia list
-    coerce_list(Type, Elements, Direction, 0, [], []).
+    coerce_list(Type, Elements, 0, [], []).

-coerce_list(Type, [Next | Rest], Direction, Index, Good, Broken) ->
-    case coerce_direction(Type, Next, Direction) of
-        {ok, Coerced} -> coerce_list(Type, Rest, Direction, Index + 1, [Coerced | Good], Broken);
+coerce_list(Type, [Next | Rest], Index, Good, Broken) ->
+    case erlang_to_fate(Type, Next) of
+        {ok, Coerced} -> coerce_list(Type, Rest, Index + 1, [Coerced | Good], Broken);
        {error, Errors} ->
            Wrapped = wrap_errors({index, Index}, Errors),
-            coerce_list(Type, Rest, Direction, Index + 1, Good, [Wrapped | Broken])
+            coerce_list(Type, Rest, Index + 1, Good, [Wrapped | Broken])
    end;
-coerce_list(_Type, [], _, _, Good, []) ->
+coerce_list(_Type, [], _, Good, []) ->
    {ok, lists:reverse(Good)};
-coerce_list(_, [], _, _, _, Broken) ->
+coerce_list(_, [], _, _, Broken) ->
    {error, combine_errors(Broken)}.

-coerce_map(KeyType, ValType, Data, Direction) ->
-    coerce_map(KeyType, ValType, maps:iterator(Data), Direction, #{}, []).
+coerce_map(KeyType, ValType, Data) ->
+    coerce_map(KeyType, ValType, maps:iterator(Data), #{}, []).

-coerce_map(KeyType, ValType, Remaining, Direction, Good, Broken) ->
+coerce_map(KeyType, ValType, Remaining, Good, Broken) ->
    case maps:next(Remaining) of
        {K, V, RemainingAfter} ->
-            coerce_map2(KeyType, ValType, RemainingAfter, Direction, Good, Broken, K, V);
+            coerce_map2(KeyType, ValType, RemainingAfter, Good, Broken, K, V);
        none ->
            coerce_map_finish(Good, Broken)
    end.

-coerce_map2(KeyType, ValType, Remaining, Direction, Good, Broken, K, V) ->
-    case coerce_direction(KeyType, K, Direction) of
+coerce_map2(KeyType, ValType, Remaining, Good, Broken, K, V) ->
+    case erlang_to_fate(KeyType, K) of
        {ok, KFATE} ->
-            coerce_map3(KeyType, ValType, Remaining, Direction, Good, Broken, K, V, KFATE);
+            coerce_map3(KeyType, ValType, Remaining, Good, Broken, K, V, KFATE);
        {error, Errors} ->
            Wrapped = wrap_errors(map_key, Errors),
            % Continue as if the key coerced successfully, so that we can give
            % errors for both the key and the value.
-            coerce_map3(KeyType, ValType, Remaining, Direction, Good, [Wrapped | Broken], K, V, error)
+            coerce_map3(KeyType, ValType, Remaining, Good, [Wrapped | Broken], K, V, error)
    end.

-coerce_map3(KeyType, ValType, Remaining, Direction, Good, Broken, K, V, KFATE) ->
-    case coerce_direction(ValType, V, Direction) of
+coerce_map3(KeyType, ValType, Remaining, Good, Broken, K, V, KFATE) ->
+    case erlang_to_fate(ValType, V) of
        {ok, VFATE} ->
            NewGood = Good#{KFATE => VFATE},
-            coerce_map(KeyType, ValType, Remaining, Direction, NewGood, Broken);
+            coerce_map(KeyType, ValType, Remaining, NewGood, Broken);
        {error, Errors} ->
            Wrapped = wrap_errors({map_value, K}, Errors),
-            coerce_map(KeyType, ValType, Remaining, Direction, Good, [Wrapped | Broken])
+            coerce_map(KeyType, ValType, Remaining, Good, [Wrapped | Broken])
    end.

 coerce_map_finish(Good, []) ->
@@ -1076,13 +1079,10 @@ lookup_variant(Name, [_ | Rest], Tag) ->
 lookup_variant(_Name, [], _Tag) ->
    not_found.

-coerce_tuple(O, N, TermTypes, Terms, Direction) ->
-    case coerce_tuple_elements(TermTypes, Terms, Direction, tuple_element) of
+coerce_tuple(O, N, TermTypes, Terms) ->
+    case coerce_elems_to_fate(TermTypes, Terms, tuple_element) of
        {ok, Converted} ->
-            case Direction of
-                to_fate -> {ok, {tuple, list_to_tuple(Converted)}};
-                from_fate -> {ok, list_to_tuple(Converted)}
-            end;
+            {ok, {tuple, list_to_tuple(Converted)}};
        {error, too_few_terms} ->
            single_error({tuple_too_few_terms, O, N, list_to_tuple(Terms)});
        {error, too_many_terms} ->
@@ -1090,19 +1090,14 @@ coerce_tuple(O, N, TermTypes, Terms, Direction) ->
        Errors -> Errors
    end.

-coerce_variant2(O, N, Variants, Name, Tag, TermTypes, Terms, Direction) ->
+coerce_variant2(O, N, Variants, Name, Tag, TermTypes, Terms) ->
    % FIXME: we could go through and add the variant tag to the adt_element
    % paths?
-    case coerce_tuple_elements(TermTypes, Terms, Direction, adt_element) of
+    case coerce_elems_to_fate(TermTypes, Terms, adt_element) of
        {ok, Converted} ->
-            case Direction of
-                to_fate ->
-                    Arities = [length(VariantTerms)
-                               || {_, VariantTerms} <- Variants],
-                    {ok, {variant, Arities, Tag, list_to_tuple(Converted)}};
-                from_fate ->
-                    {ok, list_to_tuple([Name | Converted])}
-            end;
+            Arities = [length(VariantTerms)
+                       || {_, VariantTerms} <- Variants],
+            {ok, {variant, Arities, Tag, list_to_tuple(Converted)}};
        {error, too_few_terms} ->
            single_error({adt_too_few_terms, O, N, Name, TermTypes, Terms});
        {error, too_many_terms} ->
@@ -1110,32 +1105,32 @@ coerce_variant2(O, N, Variants, Name, Tag, TermTypes, Terms, Direction) ->
        Errors -> Errors
    end.

-coerce_tuple_elements(Types, Terms, Direction, Tag) ->
+coerce_elems_to_fate(Types, Terms, Tag) ->
    % The sophia standard library uses 0 indexing for lists, and fst/snd/thd
    % for tuples... Not sure how we should report errors in tuples, then.
-    coerce_tuple_elements(Types, Terms, Direction, Tag, 0, [], []).
+    coerce_elems_to_fate(Types, Terms, Tag, 0, [], []).

-coerce_tuple_elements([Type | Types], [Term | Terms], Direction, Tag, Index, Good, Broken) ->
-    case coerce_direction(Type, Term, Direction) of
+coerce_elems_to_fate([Type | Types], [Term | Terms], Tag, Index, Good, Broken) ->
+    case erlang_to_fate(Type, Term) of
        {ok, Value} ->
-            coerce_tuple_elements(Types, Terms, Direction, Tag, Index + 1, [Value | Good], Broken);
+            coerce_elems_to_fate(Types, Terms, Tag, Index + 1, [Value | Good], Broken);
        {error, Errors} ->
            Wrapped = wrap_errors({Tag, Index}, Errors),
-            coerce_tuple_elements(Types, Terms, Direction, Tag, Index + 1, Good, [Wrapped | Broken])
+            coerce_elems_to_fate(Types, Terms, Tag, Index + 1, Good, [Wrapped | Broken])
    end;
-coerce_tuple_elements([], [], _, _, _, Good, []) ->
+coerce_elems_to_fate([], [], _, _, Good, []) ->
    {ok, lists:reverse(Good)};
-coerce_tuple_elements([], [], _, _, _, _, Broken) ->
+coerce_elems_to_fate([], [], _, _, _, Broken) ->
    {error, combine_errors(Broken)};
-coerce_tuple_elements(_, [], _, _, _, _, _) ->
+coerce_elems_to_fate(_, [], _, _, _, _) ->
    {error, too_few_terms};
-coerce_tuple_elements([], _, _, _, _, _, _) ->
+coerce_elems_to_fate([], _, _, _, _, _) ->
    {error, too_many_terms}.

 coerce_map_to_record(O, N, MemberTypes, Map) ->
    case zip_record_fields(MemberTypes, Map) of
        {ok, Zipped} ->
-            case coerce_zipped_bindings(Zipped, to_fate, field) of
+            case coerce_zipped_bindings(Zipped, field) of
                {ok, [SingleElem]} ->
                    % Singleton records aren't implemented as FATE tuples at
                    % all.
@@ -1152,31 +1147,6 @@ coerce_map_to_record(O, N, MemberTypes, Map) ->
            single_error({unexpected_fields, O, N, Names})
    end.

-coerce_record_to_map(O, N, MemberTypes, Tuple) ->
-    {Names, Types} = lists:unzip(MemberTypes),
-    Terms = tuple_to_list(Tuple),
-    % FIXME: We could go through and change the record_element paths into field
-    % paths?
-    case coerce_tuple_elements(Types, Terms, from_fate, record_element) of
-        {ok, Converted} ->
-            Map = maps:from_list(lists:zip(Names, Converted)),
-            {ok, Map};
-        {error, too_few_terms} ->
-            single_error({record_too_few_terms, O, N, Tuple});
-        {error, too_many_terms} ->
-            single_error({record_too_many_terms, O, N, Tuple});
-        {error, Errors} ->
-            correct_record_error_paths(Names, Errors)
-    end.
-
-correct_record_error_paths(Names, Errors) ->
-    CorrectOne = fun({Error, [{record_element, N} | Path]}) ->
-                     FieldName = lists:nth(N + 1, Names),
-                     {Error, [{record_element, N, FieldName} | Path]}
-                 end,
-    Corrected = lists:map(CorrectOne, Errors),
-    {error, Corrected}.
-
 zip_record_fields(Fields, Map) ->
    case lists:mapfoldl(fun zip_record_field/2, {Map, []}, Fields) of
        {_, {_, Missing = [_|_]}} ->
@@ -1217,20 +1187,10 @@ combine_errors(Broken) ->

 %%% FATE to Erlang

-% Not sure if this is needed... fate_to_erlang shouldn't fail.
-coerce_direction(Type, Term, to_fate) ->
-    erlang_to_fate(Type, Term);
-coerce_direction(Type, Term, from_fate) ->
-    fate_to_erlang(Type, Term).
-
-
-spec fate_to_erlang(Type, FATE) -> {ok, Erlang} | {error, Errors}
+-spec fate_to_erlang(Type, FATE) -> Erlang
    when Type     :: annotated_type(),
         FATE     :: gmb_fate_data:fate_type(),
-         Erlang   :: erlang_repr(),
-         Errors   :: [{Reason, [PathStep]}],
-         Reason   :: term(),
-         PathStep :: term().
+         Erlang   :: erlang_repr().
 %% @doc
 %% Convert a FATE-flavored Erlang term into a Sophia-flavored Erlang term
 %% Typically this is called by hakuzaru for you when decoding results from the
@@ -1240,83 +1200,81 @@ coerce_direction(Type, Term, from_fate) ->
 %% information.

 fate_to_erlang({_, _, integer}, S) when is_integer(S) ->
-    {ok, S};
+    S;
 fate_to_erlang({_, _, address}, {address, Bin}) ->
    Address = gmser_api_encoder:encode(account_pubkey, Bin),
-    {ok, unicode:characters_to_list(Address)};
+    unicode:characters_to_list(Address);
 fate_to_erlang({_, _, contract}, {contract, Bin}) ->
    Address = gmser_api_encoder:encode(contract_pubkey, Bin),
-    {ok, unicode:characters_to_list(Address)};
+    unicode:characters_to_list(Address);
 fate_to_erlang({_, _, signature}, Bin) ->
    Address = gmser_api_encoder:encode(signature, Bin),
-    {ok, unicode:characters_to_list(Address)};
+    unicode:characters_to_list(Address);
 %fate_to_erlang({_, _, channel}, {channel, S}) when is_binary(S) ->
-    %{ok, S};
+    %S;
 fate_to_erlang({_, _, boolean}, true) ->
-    {ok, true};
+    true;
 fate_to_erlang({_, _, boolean}, false) ->
-    {ok, false};
+    false;
 fate_to_erlang({_, _, string}, Bin) ->
-    Str = binary_to_list(Bin),
-    {ok, Str};
+    binary_to_list(Bin);
 fate_to_erlang({_, _, char}, Val) ->
-    {ok, Val};
-fate_to_erlang({O, N, {bytes, [Count]}}, Bytes) when is_bitstring(Bytes) ->
-    coerce_bytes(O, N, Count, Bytes);
+    Val;
+fate_to_erlang({O, N, {bytes, [Count]}}, {bytes, Bytes}) when is_bitstring(Bytes) ->
+    case check_bytes(O, N, Count, Bytes) of
+        ok              -> Bytes;
+        {error, Reason} -> erlang:exit(Reason)
+    end;
 fate_to_erlang({_, _, bits}, {bits, Num}) ->
-    {ok, Num};
+    Num;
 fate_to_erlang({_, _, {list, [Type]}}, Data) when is_list(Data) ->
-    coerce_list(Type, Data, from_fate);
+    Each = fun(Elem) -> fate_to_erlang(Type, Elem) end,
+    lists:map(Each, Data);
 fate_to_erlang({_, _, {map, [KeyType, ValType]}}, Data) when is_map(Data) ->
-    coerce_map(KeyType, ValType, Data, from_fate);
-fate_to_erlang({O, N, {tuple, ElementTypes}}, {tuple, Data}) ->
+    coerce_map_to_erlang(KeyType, ValType, maps:iterator(Data), #{});
+fate_to_erlang({_, _, {tuple, ElementTypes}}, {tuple, Data}) ->
    ElementList = tuple_to_list(Data),
-    coerce_tuple(O, N, ElementTypes, ElementList, from_fate);
-fate_to_erlang({O, N, {variant, Variants}}, {variant, _, Tag, Tuple}) ->
+    Elems = coerce_elems_to_erlang(ElementTypes, ElementList),
+    list_to_tuple(Elems);
+fate_to_erlang({_, _, {variant, Variants}}, {variant, _, Tag, Tuple}) ->
    Terms = tuple_to_list(Tuple),
-    {Name, TermTypes} = lists:nth(Tag + 1, Variants),
-    coerce_variant2(O, N, Variants, Name, Tag, TermTypes, Terms, from_fate);
-fate_to_erlang({O, N, {record, [SingleMemberType]}}, Data) ->
+    {Name, Types} = lists:nth(Tag + 1, Variants),
+    Elems = coerce_elems_to_erlang(Types, Terms),
+    list_to_tuple([Name | Elems]);
+fate_to_erlang({_, _, {record, [SingleField]}}, Data) ->
    % Singleton records aren't implemented as FATE tuples at all.
-    % Pretend they are, so we can get the full error indexing of the
-    % non-singletone case.
-    coerce_record_to_map(O, N, [SingleMemberType], {Data});
-fate_to_erlang({O, N, {record, MemberTypes}}, {tuple, Tuple}) ->
-    coerce_record_to_map(O, N, MemberTypes, Tuple);
+    coerce_record_to_map([SingleField], [Data], #{});
+fate_to_erlang({_, _, {record, MemberTypes}}, {tuple, Tuple}) ->
+    Terms = tuple_to_list(Tuple),
+    coerce_record_to_map(MemberTypes, Terms, #{});
 fate_to_erlang({O, N, {unknown_type, _}}, Data) ->
-    case N of
-        already_normalized ->
-            Message = "Warning: Unknown type ~p. Using term ~p as is.~n",
-            io:format(Message, [O, Data]);
-        _ ->
-            Message = "Warning: Unknown type ~p (i.e. ~p). Using term ~p as is.~n",
-            io:format(Message, [O, N, Data])
-    end,
-    {ok, Data};
-fate_to_erlang(Type, Data) ->
-    TypeStr = type_to_iolist(Type),
-    io:format("Warning: Could not coerce term into ~s. Using term as is: ~p~n", [TypeStr, Data]),
-    {ok, Data}.
+    warn_unknown_type(O, N, Data),
+    Data;
+fate_to_erlang({O, N, _}, Data) ->
+    erlang:exit({invalid, O, N, Data}).

-type_to_iolist({O, already_normalized, S}) ->
-    % Already normalized. Example output:
-    %    type {map, [string, integer]}
-    opaque_type_to_iolist(O, S);
-type_to_iolist({O, N, S}) ->
-    % Type alias. Print the alias, and then print the normalized version in
-    % parentheses. Example output:
-    %    type "my_alias" (i.e. record type {"my_record_type", [integer]})
-    io_lib:format("type ~p (i.e. ~s)", [O, opaque_type_to_iolist(N, S)]).
+coerce_elems_to_erlang(Types, Elems) ->
+    Zipped = lists:zip(Types, Elems),
+    Each = fun({Type, Elem}) -> fate_to_erlang(Type, Elem) end,
+    lists:map(Each, Zipped).

-opaque_type_to_iolist(N, {record, _}) ->
-    % N is the name of a record definition.
-    io_lib:format("record type ~p", [N]);
-opaque_type_to_iolist(N, {variant, _}) ->
-    % N is the name of a variant definition.
-    io_lib:format("variant type ~p", [N]);
-opaque_type_to_iolist(N, _) ->
-    % N is some other constructive type.
-    io_lib:format("type ~p", [N]).
+coerce_record_to_map([{Name, Type} | Types], [Term | Terms], Acc) ->
+    Coerced = fate_to_erlang(Type, Term),
+    NewAcc = maps:put(Name, Coerced, Acc),
+    coerce_record_to_map(Types, Terms, NewAcc);
+coerce_record_to_map([], [], Acc) ->
+    Acc.
+
+coerce_map_to_erlang(KeyType, ValType, Iter, Acc) ->
+    case maps:next(Iter) of
+        {KeyFATE, ValFATE, Rest} ->
+            Key = fate_to_erlang(KeyType, KeyFATE),
+            Val = fate_to_erlang(ValType, ValFATE),
+            NewAcc = maps:put(Key, Val, Acc),
+            coerce_map_to_erlang(KeyType, ValType, Rest, NewAcc);
+        none ->
+            Acc
+    end.



@@ -1354,7 +1312,7 @@ check_erlang_to_fate(Type, Sophia, Fate) ->
    end.

 check_fate_to_erlang(Type, Fate, Sophia) ->
-    {ok, SophiaActual} = fate_to_erlang(Type, Fate),
+    SophiaActual = fate_to_erlang(Type, Fate),
    % Now check that the results were what we expected.
    case SophiaActual of
        Sophia ->
@@ -1452,7 +1410,7 @@ coerce_record_test() ->

 coerce_bytes_test() ->
    {ok, Type} = annotate_type({tuple, [{bytes, [4]}, {bytes, [any]}]}, #{}),
-    check_roundtrip(Type, {<<"abcd">>, <<"efghi">>}, {tuple, {<<"abcd">>, <<"efghi">>}}).
+    check_roundtrip(Type, {<<"abcd">>, <<"efghi">>}, {tuple, {{bytes, <<"abcd">>}, {bytes, <<"efghi">>}}}).

 coerce_bits_test() ->
    {ok, Type} = annotate_type(bits, #{}),
@@ -1471,7 +1429,7 @@ coerce_unicode_test() ->
 coerce_hash_test() ->
    {ok, Type} = annotate_type("hash", builtin_typedefs()),
    Hash = list_to_binary(lists:seq(1,32)),
-    check_roundtrip(Type, Hash, Hash),
+    check_roundtrip(Type, Hash, {bytes, Hash}),
    ok.


@@ -1519,10 +1477,7 @@ singleton_record_substitution_test() ->
    {ok, {[], GOutput}} = get_function_signature(AACI, "g"),
    check_roundtrip(GOutput, #{"it" => #{"it" => 123}}, 123),
    {ok, {[], HOutput}} = get_function_signature(AACI, "h"),
-    check_roundtrip(HOutput, #{"it" => {123, 456}}, {tuple, {123, 456}}),
-    % Also check that records have accurate paths, since the implementation for
-    % record error paths is a bit fiddly.
-    {error, [{{tuple_too_many_terms, _, _, _}, [{record_element, 0, "it"}]}]} = fate_to_erlang(HOutput, {tuple, {1, 2, 3}}).
+    check_roundtrip(HOutput, #{"it" => {123, 456}}, {tuple, {123, 456}}).

 tuple_substitution_test() ->
    Contract = "
@@ -343,6 +343,12 @@ parse_expression2(_, _, _, Token) ->
 unknown_type() ->
    {unknown_type, already_normalized, unknown_type}.

+int_type() ->
+    {integer, already_normalized, integer}.
+
+int_list_type() ->
+    {{list, [integer]}, alread_normalized, {list, [int_type()]}}.
+
 expect_tokens([], Pos, String) ->
    {ok, {Pos, String}};
 expect_tokens([Str | Rest], Pos, String) ->
@@ -377,11 +383,14 @@ parse_alphanum(Type, Pos, String, ["Bits", "all"], Row, Start, End) ->
    typecheck_bits(Type, Pos, String, -1, Row, Start, End);
 parse_alphanum(Type, Pos, String, ["Bits", "none"], Row, Start, End) ->
    typecheck_bits(Type, Pos, String, 0, Row, Start, End);
+parse_alphanum(Type, Pos, String, ["variant"], Row, Start, End) ->
+    parse_anonymous_variant(Type, Pos, String, Row, Start, End);
 parse_alphanum(Type, Pos, String, [[C | _] = S], Row, Start, End) when ?IS_LATIN_LOWER(C) ->
    % From a programming perspective, we are trying to parse a constant, so
    % an alphanum token can really only be a constructor, or a chain object.
-    % Constructors start with uppercase characters, so lowercase can only be a
-    % chain object.
+    % Constructors start with uppercase characters, and we have handled our
+    % made-up 'variant' case explicitly, so the only other lowercase constants
+    % are serialized chain objects.
    try
        case gmser_api_encoder:decode(unicode:characters_to_binary(S)) of
            {account_pubkey, Data} ->
@@ -400,8 +409,8 @@ parse_alphanum(Type, Pos, String, [[C | _] = S], Row, Start, End) when ?IS_LATIN
        _:_ -> {error, {unexpected_identifier, S, Row, Start, End}}
    end;
 parse_alphanum(Type, Pos, String, Path, Row, Start, End) ->
-    % Inversely, chain object prefixes are always lowercase, so any other path
-    % must be a variant constructor, or invalid.
+    % Now having handled all lowercase terms, anything else must be uppercase,
+    % which is either a variant constructor, or totally invalid.
    parse_variant(Type, Pos, String, Path, Row, Start, End).

 typecheck_integer({_, _, integer}, Pos, String, Value, _, _, _) ->
@@ -731,6 +740,12 @@ parse_variant({O, N, {variant, Variants}}, Pos, String, [Namespace, Constructor]
        _ ->
            {error, {invalid_constructor, O, N, Namespace ++ "." ++ Constructor, Row, Start, End}}
    end;
+parse_variant({_, _, unknown_type}, Pos, String, ["None"], _, _, _) ->
+    % Special case for None without type info.
+    parse_variant3([0, 1], 0, [], Pos, String);
+parse_variant({_, _, unknown_type}, Pos, String, ["Some"], _, _, _) ->
+    % Also a special case for Some.
+    parse_variant3([0, 1], 1, [unknown_type()], Pos, String);
 parse_variant({_, _, unknown_type}, _, _, _, Row, Start, End) ->
    {error, {unresolved_variant, Row, Start, End}};
 parse_variant({O, N, _}, _, _, _, Row, Start, End) ->
@@ -753,8 +768,7 @@ get_typename(Name) ->
 parse_variant2(O, N, Variants, Pos, String, Prefix, Constructor, Row, Start, End) ->
    case lookup_variant(Constructor, Variants, 0) of
        {ok, {Tag, ElemTypes}} ->
-            GetArity = fun({_, OtherElemTypes}) -> length(OtherElemTypes) end,
-            Arities = lists:map(GetArity, Variants),
+            Arities = get_arities(Variants),
            parse_variant3(Arities, Tag, ElemTypes, Pos, String);
        error ->
            {error, {invalid_constructor, O, N, Prefix ++ Constructor, Row, Start, End}}
@@ -790,6 +804,112 @@ lookup_variant(Ident, [{Ident, ElemTypes} | _], Tag) ->
 lookup_variant(Ident, [_ | Rest], Tag) ->
    lookup_variant(Ident, Rest, Tag + 1).

+get_arities(Variants) ->
+    GetArity = fun({_, OtherElemTypes}) -> length(OtherElemTypes) end,
+    lists:map(GetArity, Variants).
+
+parse_anonymous_variant({O, N, {variant, Variants}}, Pos, String, _, _, _) ->
+    parse_anonymous_variant2({O, N, {variant, Variants}}, Pos, String);
+parse_anonymous_variant({O, N, unknown_type}, Pos, String, _, _, _) ->
+    parse_anonymous_variant2({O, N, unknown_type}, Pos, String);
+parse_anonymous_variant({O, N, _}, _, _, Row, Start, End) ->
+    {error, {wrong_type, O, N, variant, Row, Start, End}}.
+
+parse_anonymous_variant2(Type, Pos, String) ->
+    case expect_tokens(["("], Pos, String) of
+        {ok, {NewPos, NewString}} ->
+            parse_anonymous_variant3(Type, NewPos, NewString);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_anonymous_variant3(Type, Pos, String) ->
+    case parse_arities(Type, Pos, String) of
+        {ok, {Arities, NewPos, NewString}} ->
+            parse_anonymous_variant4(Type, NewPos, NewString, Arities);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_anonymous_variant4(Type, Pos, String, Arities) ->
+    case expect_tokens([","], Pos, String) of
+        {ok, {NewPos, NewString}} ->
+            parse_anonymous_variant5(Type, NewPos, NewString, Arities);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_anonymous_variant5(Type, Pos, String, Arities) ->
+    case parse_anonymous_tag(Pos, String, Arities) of
+        {ok, {Tag, NewPos, NewString}} ->
+            parse_anonymous_variant6(Type, NewPos, NewString, Arities, Tag);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_anonymous_variant6(Type, Pos, String, Arities, Tag) ->
+    ElemTypes = infer_anonymous_variant_elem_types(Type, Arities, Tag),
+    case parse_multivalue3(ElemTypes, Pos, String, []) of
+        {ok, {Terms, NewPos, NewString}} ->
+            Result = {variant, Arities, Tag, list_to_tuple(Terms)},
+            {ok, {Result, NewPos, NewString}};
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_arities(Type, Pos, String) ->
+    case next_token(Pos, String) of
+        {ok, {Token, NewPos, NewString}} ->
+            parse_arities2(Type, NewPos, NewString, Token);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_arities2(Type, Pos, String, Token = {_, _, _, Row, Start, _}) ->
+    case parse_expression2(int_list_type(), Pos, String, Token) of
+        {ok, {Arities, NewPos, NewString}} ->
+            parse_arities3(Type, NewPos, NewString, Arities, Row, Start);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_arities3({O, N, {variant, Variants}}, Pos, String, Arities, Row, Start) ->
+    ExpectedArities = get_arities(Variants),
+    case Arities == ExpectedArities of
+        true ->
+            {ok, {Arities, Pos, String}};
+        false ->
+            {error, {wrong_arities, O, N, Arities, Row, Start}}
+    end;
+parse_arities3(_, Pos, String, Arities, _, _) ->
+    {ok, {Arities, Pos, String}}.
+
+parse_anonymous_tag(Pos, String, Arities) ->
+    case next_token(Pos, String) of
+        {ok, {Token, NewPos, NewString}} ->
+            parse_anonymous_tag2(NewPos, NewString, Arities, Token);
+        {error, Reason} ->
+            {error, Reason}
+    end.
+
+parse_anonymous_tag2(Pos, String, Arities, Token = {_, _, _, Row, Start, End}) ->
+    TagCount = length(Arities),
+    case parse_expression2(int_type(), Pos, String, Token) of
+        {ok, {Tag, _, _}} when Tag < 0 ->
+            {error, {negative_tag, Tag, Row, Start, End}};
+        {ok, {Tag, _, _}} when Tag >= TagCount ->
+            {error, {invalid_tag, Tag, TagCount, Row, Start, End}};
+        Result ->
+            Result
+    end.
+
+infer_anonymous_variant_elem_types({_, _, {variant, Variants}}, _, Tag) ->
+    {_Name, ElemTypes} = lists:nth(Tag + 1, Variants),
+    ElemTypes;
+infer_anonymous_variant_elem_types({_, _, unknown_type}, Arities, Tag) ->
+    Arity = lists:nth(Tag + 1, Arities),
+    lists:duplicate(Arity, unknown_type()).
+
 %%% Record parsing

 parse_record_or_map({_, _, {map, [KeyType, ValueType]}}, Pos, String, _, _) ->
@@ -1027,15 +1147,12 @@ fate_to_iolist(Type, {tuple, Tuple}) ->
        _ ->
            tuple_to_iolist([], Tuple)
    end;
-fate_to_iolist(Type, {variant, _, Tag, Tuple}) ->
+fate_to_iolist(Type, {variant, Arities, Tag, Tuple}) ->
    case Type of
        {O, N, {variant, VariantTypes}} when Tag < length(VariantTypes) ->
            variant_to_iolist(O, N, VariantTypes, Tag, Tuple);
-        {O, N, _} ->
-            % TODO: Make up a special syntax for anonymous variant terms.
-            erlang:exit({untyped_variant, O, N});
-        _ ->
-            erlang:exit({untyped_variant, unknown_type, already_normalized})
+        {_, _, _} ->
+            anonymous_variant_to_iolist(Arities, Tag, Tuple)
    end;
 fate_to_iolist(Type, List) when is_list(List) ->
    case Type of
@@ -1130,6 +1247,22 @@ choose_variant_prefix(O, N) ->
            []
    end.

+% We don't have type information, but the Sophia programming language doesn't
+% have syntax for anonymous variants, so we have to make a syntax up. This
+% syntax is also supported when parsing terms, so that the output of one
+% contract call can be fed easily into another contract call.
+anonymous_variant_to_iolist(Arities, Tag, Tuple) ->
+    % Extract the elements of the tuple.
+    Elems = tuple_to_list(Tuple),
+
+    % Turn the arities, tag, and elements into an iolist.
+    AritiesStr = list_to_iolist(int_type(), Arities),
+    TagStr = integer_to_list(Tag),
+    FullTermsStr = list_elems_to_iolist(unknown_type(), Elems, [AritiesStr, ", ", TagStr]),
+
+    % Wrap that iolist in the anonymous 'variant' constructor.
+    ["variant(", FullTermsStr, ")"].
+
 multivalue_to_iolist([FirstType | ElemTypes], [FirstTerm | Elems]) ->
    FirstTermChars = fate_to_iolist(FirstType, FirstTerm),
    multivalue_to_iolist(ElemTypes, Elems, FirstTermChars);
@@ -1282,16 +1415,18 @@ check_parser_roundtrip(Sophia) ->
    % syntax. Let's do a lenient test.
    roundtrip_parser_lenient(unknown_type(), Sophia, Fate).

-check_parser_with_typedef(Typedef, Sophia) ->
+check_parser_with_typedef(Typedef, Sophia, UntypedSophia) ->
    % Compile the type definitions alongside the usual literal expression.
    Source = "contract C =\n  " ++ Typedef ++ "\n  entrypoint f() = " ++ Sophia,
    {Fate, Type} = compile_entrypoint_value_and_type(Source, "f"),

-    % Do a typed parse, as usual, but there are probably record/variant
-    % definitions in the AACI, so untyped parses probably don't work, and
-    % variants often have optional namespaces, so the sophia result might not
-    % match exactly, but should still be equivalent.
-    roundtrip_parser_lenient(Type, Sophia, Fate).
+    % Do a typed parse, as usual. Variant namespaces can make pretty printing
+    % ambiguous, so make the roundtrip lenient.
+    roundtrip_parser_lenient(Type, Sophia, Fate),
+    % Do an untyped parse, but using a second special Sophia expression that
+    % doesn't require type info to parse. This one *doesn't* need to be
+    % lenient, since we are specifying a distinct sophia expression.
+    roundtrip_parser(unknown_type(), UntypedSophia, Fate).

 anon_types_test() ->
    % Integers.
@@ -1323,6 +1458,10 @@ anon_types_test() ->
    check_parser_roundtrip("(1, [2, 3], (4, 5))"),
    % Map.
    check_parser_roundtrip("{[1] = 2, [3] = 4}"),
+    % Option.
+    check_parser_roundtrip("None"),
+    check_parser_roundtrip("Some(1)"),
+    check_parser_roundtrip("Some([1, 2, 3])"),

    ok.

@@ -1342,7 +1481,7 @@ string_escape_codes_test() ->
 records_test() ->
    TypeDef = "record pair = {x: int, y: int}",
    Sophia = "{x = 1, y = 2}",
-    check_parser_with_typedef(TypeDef, Sophia),
+    check_parser_with_typedef(TypeDef, Sophia, "(1, 2)"),
    % The above won't run an untyped parse on the expression, but we can. It
    % will error, though.
    {error, {unresolved_record, _, _, _}} = parse_literal(unknown_type(), Sophia).
@@ -1350,11 +1489,11 @@ records_test() ->
 variant_test() ->
    TypeDef = "datatype multi('a) = Zero | One('a) | Two('a, 'a)",

-    check_parser_with_typedef(TypeDef, "Zero"),
-    check_parser_with_typedef(TypeDef, "One(0)"),
-    check_parser_with_typedef(TypeDef, "Two(0, 1)"),
-    check_parser_with_typedef(TypeDef, "Two([], [1, 2, 3])"),
-    check_parser_with_typedef(TypeDef, "C.Zero"),
+    check_parser_with_typedef(TypeDef, "Zero", "variant([0, 1, 2], 0)"),
+    check_parser_with_typedef(TypeDef, "One(0)", "variant([0, 1, 2], 1, 0)"),
+    check_parser_with_typedef(TypeDef, "Two(0, 1)", "variant([0, 1, 2], 2, 0, 1)"),
+    check_parser_with_typedef(TypeDef, "Two([], [1, 2, 3])", "variant([0, 1, 2], 2, [], [1, 2, 3])"),
+    check_parser_with_typedef(TypeDef, "C.Zero", "variant([0, 1, 2], 0)"),

    {error, {unresolved_variant, _, _, _}} = parse_literal(unknown_type(), "Zero"),

@@ -1362,10 +1501,10 @@ variant_test() ->

 ambiguous_variant_test() ->
    TypeDef = "datatype mytype = C | D",
-    check_parser_with_typedef(TypeDef, "C"),
-    check_parser_with_typedef(TypeDef, "D"),
-    check_parser_with_typedef(TypeDef, "C.C"),
-    check_parser_with_typedef(TypeDef, "C.D"),
+    check_parser_with_typedef(TypeDef, "C", "variant([0, 0], 0)"),
+    check_parser_with_typedef(TypeDef, "D", "variant([0, 0], 1)"),
+    check_parser_with_typedef(TypeDef, "C.C", "variant([0, 0], 0)"),
+    check_parser_with_typedef(TypeDef, "C.D", "variant([0, 0], 1)"),

    ok.

@@ -1410,9 +1549,9 @@ bits_test() ->

 singleton_records_test() ->
    TypeDef = "record singleton('a) = {it: 'a}",
-    check_parser_with_typedef(TypeDef, "{it = 123}"),
-    check_parser_with_typedef(TypeDef, "{it = {it = {it = 5}}}"),
-    check_parser_with_typedef(TypeDef, "[{it = 1}, {it = 2}, {it = 3}]"),
+    check_parser_with_typedef(TypeDef, "{it = 123}", "123"),
+    check_parser_with_typedef(TypeDef, "{it = {it = {it = 5}}}", "5"),
+    check_parser_with_typedef(TypeDef, "[{it = 1}, {it = 2}, {it = 3}]", "[1, 2, 3]"),

    ok.

@@ -1421,9 +1560,9 @@ singleton_variants_test() ->
    % actually a special case; singleton variants are in fact wrapped in the
    % FATE too.
    TypeDef = "datatype wrapped('a) = Wrap('a)",
-    check_parser_with_typedef(TypeDef, "Wrap(123)"),
-    check_parser_with_typedef(TypeDef, "Wrap(Wrap(123))"),
-    check_parser_with_typedef(TypeDef, "[Wrap(1), Wrap(2), Wrap(3)]"),
+    check_parser_with_typedef(TypeDef, "Wrap(123)", "variant([1], 0, 123)"),
+    check_parser_with_typedef(TypeDef, "Wrap(Wrap(123))", "variant([1], 0, variant([1], 0, 123))"),
+    check_parser_with_typedef(TypeDef, "[Wrap(1), Wrap(2), Wrap(3)]", "[variant([1], 0, 1), variant([1], 0, 2), variant([1], 0, 3)]"),

    ok.