Hi again, I have question related to previous. To find answer I probably have to read compiler source code, but maybe you know answer already. I want some utility function which will do validation of ast, something like: valid_guard?(ast) :: boolean which I want to reuse to assume that given expre…

If you want to know if a macro is a valid guard you can use Macro — Elixir v1.20.2 and then traverse the AST, checking if all the calls in that AST are guards themselves. If you wish to know whether a function it pure it is a much more difficult task, one not possible with the Elixir compiler today…

[image] lpil: What do you mean by this? I mean that both Erlang and Elixir compilers don’t allow application of impure functions in guard expressions. And I just want to reuse this utility. Check that given AST is pure for sure, either that it might be impure.

They don’t track if functions are pure, instead they have a small list of permitted functions and operators, and if any other functions are used then the code is rejected by the compiler. In Elixir it is the same process I outlined above with macro expansion. Purity inference isn’t need as being pu…

[image] lpil: they have a small list of permitted functions Thanks, I understand, that’s completely fine for my proposes. I maintain this library ExEnv — ExEnv v0.3.4 And atm it don’t allow any function application. But I want to allow application of fu…

I just don’t want to re-invent the wheel, and deal with tricky possibilities like import Kernel, except: [{:'-', 1}] import UnpureOverride, only: [{:'-', 1}] Erlang/Elixir compiler already have utility to deal with this kind of stuff and reject it in guards because of possible impurity

No, not really. Erlang/Elixir just have defined set of “guard safe” functions which are allowed. There is much broader set of pure functions that will not be allowed in guards.

[image] tim2CF: Erlang/Elixir compiler already have utility to deal with this kind of stuff and reject it in guards because of possible impurity They do not have this functionality I’m afraid. You’re effectively wanting to write a kind of static type system for Erlang- it would be a large pi…

[image] lpil: checking if all the calls in that AST are guards themselves. I think it will be quite enough for purposes of my library. Do you know name of utility function which checks that given AST is valid guard? Or maybe some guesses where to search it?

[image] tim2CF: I think it will be quite enough for purposes of my library. I suspect it will not be, you will be limited to just these functions: !=/2 !==/2 */2 +/1 +/2 -/1 -/2 //2 <=/2 ==/2 ===/2 >/2 >=/2 abs/1 and/2 binary_part/3 bit_size/1 byte_size/1 ceil/1 div/2 elem/2 floor/1 hd/1 in…

@lpil and @hauleth Thanks, I know how to do it now!

Elixir Programming Language Forum

Purity validation

Questions & Help Questions

hauleth March 31, 2020, 10:54am 11

erl_internal:guard_bif/2 or erl_lint:is_guard_test/1