Re: Spad and inductive types

Ooops, I overlooked something.

>> ---BEGIN bbb.as
>> #include "aldor"
>> #include "aldorio"
>>
>> #library EXPR "aaa.ao"
>> import from EXPR;
>>
>> extend Expr: OutputType == add {
>>     import from 'MkInt', 'MkAdd', 'MkMul';
>>     import from Integer;
>>     (tw: TextWriter) << (x: %): TextWriter == {
>>         x case MkInt => tw << x.MkInt;
>>         x case MkAdd => {
>>             (a, b) := x.MkAdd;
>>             tw << "(" << a << "+" << b << ")";
>>         }
>>         x case MkMul => {
>>             (a, b) := x.MkMul;
>>             tw << "(" << a << "*" << b << ")";
>>         }
>>         tw;
>>     }
>> }

> The use of case above seems very unnatural to me. Is it
> possible to extend each constructor (e.g. MkInt, MkMul, etc.)
> separately.

I don't understand. In my case Mk??? are not domain constructors, so I 
have no way to "extend" anyway.

On the other hand, why is that case business so unnatural? Expr is a 
Union, so in order to be type safe, I have to figure out in which part 
of the union the element actually lives. You do the same thing in your 
implementation of eval on 
http://wiki.axiom-developer.org/SandBoxInductiveType .

>> main(): () == {
>>     import from Integer;
>>     e1: Expr := MkInt 1;       stdout << "e1 = " << e1 << newline;
>>     e2: Expr := MkInt 2;       stdout << "e2 = " << e2 << newline;
>>     e3: Expr := MkInt 3;       stdout << "e3 = " << e3 << newline;
>>     a1: Expr := MkAdd(e1, e2); stdout << "a1 = " << a1 << newline;
>>     m1: Expr := MkMul(a1, e3); stdout << "m1 = " << m1 << newline;
>> }
>> main();
>> ---END bbb.as

> Ralf, these are just general comments about your approach and
> aren't intended to be particularly critical.

Although I felt that it was the most critical reaction on one of my 
mails that I have ever experienced from you, I know that you do that to 
contribute to understanding the situation. I don't feel offended.

By the way. Today I have learned how to include an integer into the 
"left" or "right" part of Union(left: Integer, right: Integer). There 
appears only an example in the AUG, but not a formal description.

Ralf