Your two examples aren’t quite equivalent.

  true = false

raises a match error while

  true <- false

in a with statement doesn’t.

You can actually use true = false in your with statement, but it will still raise the match error.

> I understand why with could not work with the = matching operator (it's a macro)

Not sure what you mean - `with` _can_ use the `=` operator, e.g. you could write:

      with true = is_email_address?(email),
         true = EmailAddresses.is_available(email) do
        # something
      end

Although this is rather pointless as it's functionally equivalent to just writing:

     true = is_email_address?(email)
     true = EmailAddresses.is_available(email)
     # something

`=` is useful inside `with` if you have a clause that _must_ return a particular value or it's an error, i.e. you don't need to match on any other possible return value. But if you don't have at least one clause with `<-` then `with` achieves nothing.

Also, why would the fact that `with` is a macro mean that it can't use `=`?