From 5d0874a8f9fd617308d9024783db1e4e24268184 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20Muska=C5=82a?= Date: Fri, 27 Apr 2018 12:40:07 +0200 Subject: Introduce is_map_key/2 guard BIF This complements the `map_get/2` guard BIF introduced in #1784. Rationale. `map_get/2` allows accessing map fields in guards, but it might be problematic in more complex guard expressions, for example: foo(X) when map_get(a, X) =:= 1 or is_list(X) -> ... The `is_list/1` part of the guard could never succeed since the `map_get/2` guard would fail the whole guard expression. In this situation, this could be solved by using `;` instead of `or` to separate the guards, but it is not possible in every case. To solve this situation, this PR proposes a `is_map_key/2` guard that allows to check if a map has key inside a guard before trying to access that key. When combined with `is_map/1` this allows to construct a purely boolean guard expression testing a value of a key in a map. Implementation. Given the use case motivating the introduction of this function, the PR contains compiler optimisations that produce optimial code for the following guard expression: foo(X) when is_map(X) and is_map_key(a, X) and map_get(a, X) =:= 1 -> ok; foo(_) -> error. Given all three tests share the failure label, the `is_map_key/2` and `is_map/2` tests are optimised away. As with `map_get/2` the `is_map_key/2` BIF is allowed in match specs. --- lib/hipe/cerl/erl_bif_types.erl | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'lib/hipe') diff --git a/lib/hipe/cerl/erl_bif_types.erl b/lib/hipe/cerl/erl_bif_types.erl index fe6ab0659c..48ce641ab9 100644 --- a/lib/hipe/cerl/erl_bif_types.erl +++ b/lib/hipe/cerl/erl_bif_types.erl @@ -665,6 +665,8 @@ type(erlang, is_map, 1, Xs, Opaques) -> check_guard(X, fun (Y) -> t_is_map(Y, Opaques) end, t_map(), Opaques) end, strict(erlang, is_map, 1, Xs, Fun, Opaques); +type(erlang, is_map_key, 2, Xs, Opaques) -> + type(maps, is_key, 2, Xs, Opaques); type(erlang, is_number, 1, Xs, Opaques) -> Fun = fun (X) -> check_guard(X, fun (Y) -> t_is_number(Y, Opaques) end, @@ -2374,6 +2376,8 @@ arg_types(erlang, is_list, 1) -> [t_any()]; arg_types(erlang, is_map, 1) -> [t_any()]; +arg_types(erlang, is_map_key, 2) -> + [t_any(), t_map()]; arg_types(erlang, is_number, 1) -> [t_any()]; arg_types(erlang, is_pid, 1) -> @@ -2396,7 +2400,7 @@ arg_types(erlang, map_size, 1) -> [t_map()]; %% Guard bif, needs to be here. arg_types(erlang, map_get, 2) -> - [t_map(), t_any()]; + [t_any(), t_map()]; arg_types(erlang, make_fun, 3) -> [t_atom(), t_atom(), t_arity()]; arg_types(erlang, make_tuple, 2) -> -- cgit v1.2.3