On Tue, Aug 12, 2003 at 12:30:27PM +0200, Johannes Waldmann wrote:
On Mon, 11 Aug 2003, Tomasz Zielonka wrote:
The Tree datatype in new Data.Tree module has a Show instance ...
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On the other hand, it is my opinion that for a clean program design, you should normally define your own `data' (or `newtype') types, rather than use exisiting ones by `type' synonyms.
this may lead to somewhat larger program texts, but you'll find that they are more readable, and extendable. (Compare adding another component to a tuple, and to a record).
this also gives you the opportunity to define class instances in any way you want.
I agree with you. I often define my own types using 'data' and 'newtype', even for things like IP adresses and numeric identifiers, because I don't need and don't want many operations that integral types provide but are meaningles in these applications. I also find datatypes with named fields convenient. And I rarely define type synonyms, probably only for some involved combinations of monad transformers. However, I think that there are some types so generic, that they deserve including in standard libraries. One example is a list - how often do you define your own list type? But lists form a subset of trees, and trees form a subset of graphs, so it would be nice to have them delivered with GHC even if they would only be used in toy applications. Best regards, Tom -- .signature: Too many levels of symbolic links