Negation

johndearle at cox.net johndearle at cox.net
Tue Feb 9 14:48:45 EST 2010

```My impression is that combinatory logic figures prominently in the design of Haskell and some of the constructs seem to be best understood as combinatorial logic with syntactic sugar. One could predict from this a number of things. One of such is the language would at some points seem counter intuitive, albeit rational. I am concerned that those who lose sight of this, or perhaps never understood this and don't care to, may lose touch with the language's intent. If it is an outcome of combinatorial logic it is likely correct. The problem may lie else where.

The example given "rationale" suggests that the problem centers on the language designers being in possession of a necessary condition for correctness, but not a sufficient condition. If this is the case, there are two courses of action that are available to you/us. Solve the problem, as in work out all the necessary conditions so that you are in possession of a sufficient condition or give up the attempt to solve the problem altogether, throw up your hands and admit you failed, proclaiming that the naive solution found was and is worse than the problem. It may even turn out that as you become familiar with the alleged solution, that it has charm, in that it brings you flowers and you discover that he isn't all that bad.

---- Christian Maeder <Christian.Maeder at dfki.de> wrote:
> > | I imagine it would be something like deleting the production
> > |
> > |     lexp6    ->      - exp7
>
> The rational for the current choice was the example:
>
> f x = -x^2
>
> > | and adding the production
> > |
> > |     exp10    ->      - fexp
>
> But I would also recommend this change.
>
> It would also make sense to allow "-" before "let", "if" and "case" or
> another "-" expression, but that's a matter of taste.
>
> Cheers Christian
> _______________________________________________