[m-rev.] for review: don't allow nondefault mode functions in terms

[Zoltan Somogyi]

On Sun, 1 Nov 2015 11:15:06 +1100, Peter Wang <novalazy at gmail.com> wrote:
> Isn't it strange if an instantiatedness tree `I' has all nodes bound
> but I \=< ground?

A big part of the problem is that "ground" can mean several things,
closely related but subtly different. You cannot solve this problem
without making the differences explicit, preferably in terminology
as well as in code. With some of the things you can mean by "ground",
yes, that is strange; with other meanings, it isn't.

> Another solution to the problem is to verify at runtime that a
> higher-order function has a default mode before calling it, otherwise
> throwing an exception.

That would be overkill.

Zoltan.