Mon, 27 Nov 2000 09:30:17 +0100, Bernd Holzmüller <[EMAIL PROTECTED]> pisze:
> Consider you have a data structure (e.g. an abstract syntax tree)
> consisting of nodes belonging to different data types. The difficulty
> is to write a function that abstracts from the traversal of that
> tree. I.e.
> Ashley Yakeley wrote:
> A better question might be, having extended the type system (and indeed
> the notion of 'type') in this way, how do I need to modify the concept of
> 'principal type'?
> ...
> There are two different kinds of 'general' here. Informally, you want the
> type most general
Hi Christian,
Your suggestion is of course possible. However, it imposes an overhead
which I would like to avoid. Consider you have a data structure (e.g. an
abstract syntax tree) consisting of nodes belonging to different data
types. The difficulty is to write a function that abstracts from the
Ashley Yakeley writes:
> At 2000-11-24 02:02, Bernd =?iso-8859-2?Q?Holzm=FCller?= wrote:
>
>> When I got to know Haskell, I was expecting a construct for union types
>> like:
>>
>> data B = ...
>> data C = ...
>> type A = B | C | D -- A accepts values of either B or C or D (cf. the
>> "Either a
Hi Bernd,
> data B = ...
> data C = ...
> type A = B | C | D -- A accepts values of either B or C or D (cf. the
> "Either a" type in the Prelude)
What about the construction of a union type in Haskell like this?:
data B = B1 | B2
data C = C1 | C2 | C3
data D = D1 | D2
data A = UB
Fergus Henderson <[EMAIL PROTECTED]> writes:
[...]
> (2) Allow pattern matching on values of particular types,
> using `case'.
[...]
> If we allow (2), then some programming mistakes that previously
> were type errors would instead become just inexhaustive pattern
> matches for wh
At 2000-11-24 03:14, Fergus Henderson wrote:
>> Is there any reason for this restriction
>> in the Haskell type system? Does this lead to losing the principal type
>> property?
>
>If you allow (2) above, there may be serious problems for
>principal types. For example, consider
>
> f x = ca
At 2000-11-24 02:02, Bernd =?iso-8859-2?Q?Holzm=FCller?= wrote:
>When I got to know Haskell, I was expecting a construct for union types
>like:
>
> data B = ...
> data C = ...
> type A = B | C | D -- A accepts values of either B or C or D (cf. the
>"Either a" type in the Prelude)
>
>but this i
On 24-Nov-2000, Bernd Holzmüller <[EMAIL PROTECTED]> wrote:
> There is one thing I was really missing in all these projects: the
> existence of union types (i.e. the union of value sets of two existing
> data types)
Mercury has a similar type system to Haskell.
This question came up a lot during
I am about to finish my PhD, where I used the Vienna Definition Language
(VDL) to specify the semantics of some programming language constructs.
In order to verify this semantics description using a type checker and
by dynamic execution, I found and used Haskell as the language of choice
to map th
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