Hi Perhaps the error message for an unimplemented protocol could be made more friendly. I don't have any suggestions myself, but perhaps Edouard had some ideas for Map.drop that could be generalised to all protocols.
Cheers, Louis On Sun, 13 Jan 2019, 12:02 José Valim, <jose.va...@plataformatec.com.br> wrote: > It would be possible only if you manually write error messages for every > existing function. There is no trivial way to automate it without adding a > type system. > > > *José Valim* > www.plataformatec.com.br > Skype: jv.ptec > Founder and Director of R&D > > > On Sun, Jan 13, 2019 at 12:42 PM Edouard Mnd <edouard.mena...@gmail.com> > wrote: > >> Oh i see so the only simple option would be to add something along the >> line `drop(map, a) when is_atom(a)` but it would mean making the widening >> the api surface. >> Maybe the answer does not lie directly in elixir core but in something >> that would run after the elixir compiler able to give suggestions about the >> errors ? It clearly is not the scope of the discussion but I would be >> interested to know what you think about it and what elixir api could be >> used to make such a hint/suggestion layer. >> >> On Saturday, January 12, 2019 at 8:38:20 PM UTC+1, Andrea Leopardi wrote: >>> >>> The problem here is that Map.drop/2 expects a term as the second >>> argument that implements the Enumerable protocol. This means that >>> realistically we can't check for a specifically supported data type or >>> types, since anything could implement the Enumerable protocol. For example, >>> I might implement Enumerable for atoms and then your code would work. >>> >>> On Sat, 12 Jan 2019 at 19:10, Edouard Mnd <edouard...@gmail.com> wrote: >>> >>>> Hi, >>>> >>>> I have been running into the same issue again and again with elixir >>>> where I get a weird error like >>>> >>>>> (Protocol.UndefinedError) protocol Enumerable not implemented for >>>>> "foo". This protocol is implemented for: DBConnection.PrepareStream, DBCo >>>>> nnection.Stream, Date.Range, Ecto.Adapters.SQL.Stream, File.Stream, >>>>> Function, GenEvent.Stream, HashDict, HashSet, IO.Stream, List, Map, >>>>> MapSet, >>>>> Postgr ex.Stream, Range, Stream, StreamData, Timex.Interval >>>>> >>>> when doing `Map.drop(foo, :sth). >>>> Obviously i'm doing something wrong : I should give a list as a second >>>> argument but I keep forgetting and I bet i'm not the only one. >>>> My proposal would consist in handling this case explicitly either by >>>> allowing for such a case to work or giving back a clear error message such >>>> as "Are you trying to do Map.drop(foo,[:sth]) ?". >>>> I'm greatly inspired by the rust language in asking this, indeed rust >>>> gives you really great error messages when doing silly things. >>>> >>>> I hope you find my proposal clear and interesting as it clearly is not >>>> just about Map.drop but also about giving better error messages to the >>>> developer when doing silly things which I think is important. >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "elixir-lang-core" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to elixir-lang-co...@googlegroups.com. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/elixir-lang-core/550f8801-c0d9-41ea-947a-8c3ee483c76a%40googlegroups.com >>>> <https://groups.google.com/d/msgid/elixir-lang-core/550f8801-c0d9-41ea-947a-8c3ee483c76a%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> -- >>> >>> Andrea Leopardi >>> an.le...@gmail.com >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "elixir-lang-core" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to elixir-lang-core+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/elixir-lang-core/93fd3c38-c285-48b8-87d1-898fe45a1afc%40googlegroups.com >> <https://groups.google.com/d/msgid/elixir-lang-core/93fd3c38-c285-48b8-87d1-898fe45a1afc%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to elixir-lang-core+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4%2BUJwM4cyif%2ByBtRyge6mJ-uR%3DAiJuFkJnnazyN6-JQ-w%40mail.gmail.com > <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4%2BUJwM4cyif%2ByBtRyge6mJ-uR%3DAiJuFkJnnazyN6-JQ-w%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. 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