[erlang-questions] Use of logical "not" in `case`

[Robert Carbone]

I am with Loïc, I'd be tripped—

*A flurry of thoughts · · · *

     "When writing a case statement based on a boolean expression"

· As we're only working with a boolean(), why use the case at all?
    That may be where the confusion is coming form.
    The big thing happening here is the true or false, I believe using 
variables makes that clearer.

      foo(Status, Thingy, Assignments)
        ->
                      TF = maps:is_key(Thingy, Assignments),
                         if
            TF =:= false -> {Status, Assignments}
          ; TF =:= true  ->          Assignment  = 
fomulate_assignment(Thingy),
                                  NewAssignments = maps:put(Thingy, 
Assignment, Assignments),
                       {assigned, NewAssignments}
                       end.

· I tend to put the shorter clause one near the top(see above), so the 
reader can get take a breath quicker.

· I am have no problem, mentally, saying "otherwise" when I see a  "; 
true ->" because of the way Erlang treats 'if' expressions. So it can 
come second just as easily.

· The other day I read that the brain can handle complex data types way 
better than it candle handle complex logic... I guess anything to does 
not add to the confusion, not unlike the 'not', isn't that terrible. ;)

· What Dave Thomas said at last year's conference may apply here:

         Programming is Nested Composable Transformation
         Rules should be:
            1. Work out what should be true ->
            2. Make it true  ( establishing initial conditions )
            3. Keep it true   ( during transformations )
///                Also, mentioned,/
///             · Ask yourself, how does the language encourage you to 
think about things?/
///             · If you make it easier to think about things in terms 
of reducers,
//////the quality of programming will increase.

Cheers,
Rob Carbone
scriptculture.com
/



On 2/9/18 4:40 AM, Loïc Hoguin wrote:
> On 02/09/2018 10:31 AM, zxq9@REDACTED wrote:
> [...]
>> foo(Status, Thingy, Assignments) ->
>>      case not maps:is_key(Thingy, Assignment) of
>>          true ->
>>              Assignment = fomulate_assignment(Thingy),
>>              NewAssignments = maps:put(Thingy, Assignment, Assignments),
>>              {assigned, NewAssignments};
>>          false ->
>>              {Status, Assignments}
>>      end.
> [...]
>> This isn't a big deal either way of course (I find them both equally 
>> readable), but I am curious if anyone has a strong opinion on the 
>> issue and why. Which would you prefer to encounter when reading a 
>> project to understand how it works on github?
>
> Oh boy. I would definitely get tripped by this. Or at the very least 
> have some eyebrow action.
>
> I have no problem with it in something like C because there's usually 
> no 'else' clause in these cases and it's therefore very easy to read 
> the intent.
>
> But in Erlang's case what you effectively do is invert the boolean 
> value below and that requires a little more gymnastic. And I don't 
> think it matches what one would say in a conversation because why 
> would you mention the case where nothing happens at all?
>

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