[m-users.] Conjunction as an operator

[Volker Wysk]

Am Samstag, den 12.10.2019, 17:42 -0500 schrieb Julian Fondren:
> On 2019-10-12 17:32, Volker Wysk wrote:
> > Hi!
> > 
> > I need a conjunction of two terms, like this:
> > 
> >     X = (Str \= "" & Str \= ".")
> > 
> 
> What is X supposed to be, here? What is its type? Whats a possible
> value that it could have? 

X should be a boolean value, "yes" or "no". But I've messed up, it
shouldn't be done this way. I wanted to use it as the predicate in a
"filter" call, like:

slice_path_1(PfadL) = 
    filter( (func(Str::in) = Str \= [] && Str \= ['.']),
            split(PfadL)
          ).

Now I've figured it out:

slice_path_1(PfadL) = 
    filter( (pred(Str::in) is semidet :-
                 Str \= [],
                 Str \= ['.']),
            split(PfadL)
          ).

Old habits from Haskell.


> If you want to fail if Str is either ""
> or ".", you can do that with any of
> 
>    Str \= "", Str \= "."
> 
>    not (Str = "" ; Str = ".")
> 
>    ( if Str = "" ; Str = "." then fail else true )
> 
> A,B and A&B only differ operationally: A and B might be executed in
> parallel in the second case.
> 
> > This doesn't work. I'm sure I don't understand what's going on.
> > Could
> > somebody please tell me how this is done?
> > 
> > Volker