I afraid you missed my point, I might have expressed it poorly. Let's assume I have a simple type: {is_atom(), is_number(), is_binary()}. I want to define a guard to match it. Without reusing I can write a function accepting it:
func({x, y, z}) when is_atom(x) and is_number(y) and is_binary(z), do: true but then I want to define another function which expects the same tuple: another({x, y, z}) when is_atom(x) and is_number(y) and is_binary(z), do: true I don't have a way to define a custom guard to match tuple elements since there is no pattern matching in defguard nor there is `elem` in guards. So both options don't work: defguard is_mytype({x, y, z}) when is_atom(x) and is_number(y) and is_binary(z) nor defguard is_mytype(x) when is_atom(elem(x, 0)) and is_number(elem(x, 1)) and is_binary(elem(x, 2)) Furthermore, I would want to define a function that receives a value of my type inside of complex structure: function({:ok, {x, y, z}}) when is_atom(x) and is_number(y) and is_binary(z), do: true it would be cool to have it defined as function({:ok, x}) when is_mytype(x), do: true P.S. Actually, I've found that `elem` works in guards, so I can define my guard without pattern matching. That's good for now, but func({x, y, z}) when is_atom(x) and is_number(y) and is_binary(z), do: true sounds cooler, IMHO =) On Wednesday, November 7, 2018 at 8:20:22 PM UTC+2, Louis Pilfold wrote: > > Hi Sergiy > > The functionality you've described can be implemented with macros, no need > to modify Elixir or Erlang. > > To start it could be as simple as defining guards that assert nothing in > the production environment. > > defmodule Test do > if Mix.env() == :prod do > defguard is_my_type(x) when true > else > defguard is_my_type(x) when is_atom(x) > end > > def go(x) when is_my_type(x) do > x > end > end > > This could be a little error prone though as unless you remember to apply > the guard to every clause of the function your logic may change when they > are removed. Even if you apply them to every clause if you use exceptions > as flow control you may run into problems as values that previously would > result in a FunctionClauseError would be passed though. > > Plenty to think about! Perhaps experiment with a little proof of concept > library and see what happens :) > > Cheers, > Louis > > On Wed, 7 Nov 2018 at 17:44 Sergiy Kukunin <sergey....@gmail.com > <javascript:>> wrote: > >> Thanks for the answers. Just want to note, that I don't want to invent >> type system such as in statically typed languages. I mean more about >> defining schemas we can check different values with. All pattern matching, >> guards and typespec might work for this. Furthermore, it would be cool to >> make it composable and reusable (such as defguards and typespecs right now). >> >> Just to conclude, I would suggest that either of these would improve the >> safety and convenience of the language: >> - allow pattern matching in custom guards (either via the built-in guard >> such as `Kernel.match?/2` or by extending the defguard syntax) >> - having a macro to check whether a value corresponds to a defined @type >> >> What's about such syntax? >> >> defguard is_mytype({x, y}) when is_atom(x) and is_number(y) >> >> def test({:ok, value}) when is_mytype(value), do: true >> def test(_), do: false >> >> test({:ok, {:hello, 5}}) # should be true >> test({:ok, {2, 5}}) # should be false >> >> There are a couple of reasons I've raised this question: >> >> - do I miss something? don't I try to solve the problem in a wrong way? >> - to estimate how hard is it to implement in a 3rd-party library or does >> it require changes to core Elixir/ErlangVM >> >> Thanks >> >> >> On Wednesday, November 7, 2018 at 7:20:47 PM UTC+2, Louis Pilfold wrote: >> >>> Hi all >>> >>> The desire for more safety in Elixir is reasonable, both at compile time >>> and at runtime. >>> >>> The core team have previously experimented with introducting a compile >>> time type checking system, and we also have the dialyser and gradualizer >>> tools that can be used with Elixir. >>> >>> Checking at runtime is something we already do in Elixir and Erlang >>> through the use of pattern matching and guards such as `is_binary/1`. >>> A library of macros that automates these checks could be an interesting >>> project, perhaps an area worth exploring for members of the community. >>> >>> Cheers, >>> >> Louis >>> >>> On Wed, 7 Nov 2018, 16:46 Ivan Yurov, <ivan.y...@gmail.com> wrote: >>> >> If you want type-safety why not to just pick a strongly typed language, >>>> like Ocaml for example? Elixir is bound to Erlang VM and will never >>>> provide >>>> any features like you're describing that are not supported by Erlang. And >>>> I >>>> don't think type-checking ever happens at runtime in any language. >>>> >>>> On Wednesday, November 7, 2018 at 12:00:53 PM UTC+1, Sergiy Kukunin >>>> wrote: >>>>> >>>>> Hello there. This is my first message to the elixir group. Thanks for >>>>> the great language. >>>>> >>>>> While I'm writing my code, I want to make functions to be safer. It's >>>>> bad practice if a function accepts unexpected input and pass it further, >>>>> and it blows in a completely different part of a system. >>>>> >>>>> At first glance, I have pattern matching, but it's pretty limited. It >>>>> becomes really powerful in conjunction with guards, so I can write a >>>>> signature to match literally everything. >>>>> But they hard to re-use, If I have multiple functions operating with >>>>> the same object. Yes, I can define a custom guard, but can I use pattern >>>>> matching there? `Kernel.match?/2` doesn't work, so I'm limited with only >>>>> guards in my custom guards. >>>>> >>>>> Another thing that we have typespecs. It seems exactly what I'm >>>>> looking for: you have a wide set of built-in types, and I can easily >>>>> compose and reuse my own types. The problem with it, that it doesn't >>>>> affect >>>>> runtime. I know about static analyzer `dialyzer`, but I'm not sure it >>>>> will >>>>> catch all cases since it's a static check, not a runtime. >>>>> >>>>> Let's assume a simple function, that wraps a value into a list: >>>>> >>>>> @spec same(number()) :: [number()] >>>>> def same(number) do >>>>> [number] >>>>> end >>>>> >>>>> I'm sure the `dialyzer` won't complain since a signature is valid. But >>>>> what if I do: `same("abc")` ? What will prevent Elixir from returning a >>>>> wrong type? I guess, nothing. >>>>> An example from a real life: I have a function, that accepts a custom >>>>> shaped value (using tuples) and feeds it to a queue. Then, in the totally >>>>> different part of the system, a consumer gets values from the queue. And >>>>> when a wrong value was fed on the producer side, it blows on the consumer >>>>> side. So I decided to put some constraints on the producer side to fail >>>>> fast. >>>>> >>>>> Yes, I could define a guard, but again, if I have a pretty complex >>>>> type instead of the simple `number`, I had to duplicate the type >>>>> defining: >>>>> one for typespec, another is for a custom guard (which is limited, since >>>>> I >>>>> can't use pattern matching there). >>>>> >>>>> Wouldn't it be cool, If we had a mechanism to assert a value to its >>>>> type, in runtime? To avoid performance penalty we could enable it only >>>>> for >>>>> runtime. Is there a way right now to check whether a value corresponds to >>>>> a >>>>> type in runtime? Can I implement a custom macro to provide a good DSL for >>>>> this? Is it helpful at all? >>>>> >>>>> P.S. You may say, use structs and pattern matching would work in this >>>>> case. But what if my type is better represented by a tuple: {atom(), >>>>> pos_integer(), string()}. Converting it to a struct might complicate a >>>>> way >>>>> to work with the value. >>>>> >>>> -- >>>> 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/8c4d9dac-134d-471c-a402-e9696bf5aecf%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/elixir-lang-core/8c4d9dac-134d-471c-a402-e9696bf5aecf%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-co...@googlegroups.com <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/elixir-lang-core/c7e602a5-a694-46f9-99a5-983b4d50eea0%40googlegroups.com >> >> <https://groups.google.com/d/msgid/elixir-lang-core/c7e602a5-a694-46f9-99a5-983b4d50eea0%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. 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