"Bill Page" <[EMAIL PROTECTED]> writes:
| Quoting Ralf Hemmecke <[EMAIL PROTECTED]>:
|
| >
| >> All the exports that appear are basically the
| >>> exports of the Union (OK, Union still has a few more.)
| >
| >>> ---BEGIN aaa.as
| >>> #include "aldor"
| >>> #include "aldorio"
| >>>
| >>> define ET: Category == with; -- ExpressionType
| >>> Expr: ET with {
| >>> MkInt: Integer -> %;
| >>
| >> It doesn't look right to me that the MkInt constructor
| >> takes a specific integer as a parameter while MkAdd and
| >> MkMul take a type.
| >
| > Huh? The MkAdd also take specific elements of Expr. That
| > is not different from an element of Integer. It's at the
| > same level.
|
| No, I think there is a serious misunderstanding here. What
| Gaby is talking about are "algebraic data types". See for
| example:
|
| http://en.wikipedia.org/wiki/Algebraic_data_type
|
| In Gaby's example Haskell code:
|
| data Expr = MkInt Int
| | MkAdd Expr Expr
| | MkMul Expr Expr
|
| MkInt is *not* a function which when given an Integer
| returns something of type Expr.
I disagree: MkInt *IS* such a function.
| It is type *constructor*,
^^^^^^^^^^^^^^^^^^^^
No, that is incorrect.
| that is, when given 'Int' MkInt returns a subtype of Expr. The
| difference might seem a little subtle at first but we
| can clearly distinguish such things in languages like
| Spad and Aldor.
I believe you're confused. MkInt, MkAdd, and MkMul are *data*
constructors -- I believe I've said that many times.
A type constructor is a different thing.
-- Gaby
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