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Newsgroups: comp.lang.ada
Date: Sat, 7 Apr 2018 03:17:25 -0700 (PDT)
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Subject: Re: Standard."-" provided to "with function "-" (VAL1 : in
 VALUE_TYPE) return VALUE_TYPE is <>;" refused:
From: Mehdi Saada <00120260a@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:51377
Date: 2018-04-07T03:17:25-07:00
List-Id: <comp.lang.ada>

You may be right, in fact I think you are. When checking syntax/semantic, letting minus operators to <> works. But I uncovered a bigger problem with gps' "keep going" option: circular instantiations...
originally: neither expressions nor spreadsheets.formula_cells were generics. They both used INTEGER.
And they could call each other: Formula_cells needs expression to calculate stuff, and expressions.formula_type (or whatever) needs spreadsheets to define a new syntax type which is aware of spreadsheets coordinates.
I don't know how it was meant to be (I won't rewrite it to be non-generic), but it had to work, so I guess being generics made both two packages not only "with" each other, but INSTANTIATE each other.
I'll have to think about the *design* a bit.