[Proposal] Add compiler error when using = instead of <- in with statement

[Bruno Rafael]

Hello all,

I mistyped the match operator with an equal signal (=) using the with statement and the compiler didn't warn. When calling a function with args that don't match the condition of a with statement where the match operator is a = the code breaks. I don't know if it's the desired behavior but when using the with statement and some condition doesn't match I would expect it to go to the else statement. Should the compiler warn in these cases?

elixir 1.10.3

erlang 22.3.4.1

Regards,

Bruno

[Greg Vaughn]

Any expression is allowed in the comma-separated steps of a with expression. You can put in IO.inspect(myvar) (which I often use for debugging purposes). A pattern match (=) is an allowed expression. It is not a bug.

-Greg Vaughn

> On Aug 12, 2020, at 7:42 PM, Bruno Rafael <brunora...@gmail.com> wrote:
>
> Hello all,
>
> I mistyped the match operator with an equal signal (=) using the with statement and the compiler didn't warn. When calling a function with args that don't match the condition of a with statement where the match operator is a = the code breaks. I don't know if it's the desired behavior but when using the with statement and some condition doesn't match I would expect it to go to the else statement. Should the compiler warn in these cases?
>
> elixir 1.10.3
> erlang 22.3.4.1
>

> <Screenshot from 2020-08-12 21-40-20.png>
>
> Regards,
> Bruno
>

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> <Screenshot from 2020-08-12 21-40-20.png>

[Austin Ziegler]

Also, the `<-` is the “capturing” match that goes to `else`; `=` is explicitly permitted for pattern matching invariants (e.g., there is no meaningful recovery from that failed pattern match).

-a

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