Re: mapM_ for bytestring

On Sun, 01 Sep 2013 23:27:20 +0400, Henning Thielemann wrote:

On Sun, 1 Sep 2013, Artyom Kazak wrote:

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On Sun, 01 Sep 2013 22:55:10 +0400, Henning Thielemann wrote:

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A possible solution might be fusion rules for ByteString.unpack and mapM_.

Except that such rules would require a hand-written version of mapM_ anyway.

I agree that it can be written, it’s just that I don’t see why it should be in some obscure place instead of Data.ByteString.

This rule should of course be part of Data.ByteString. RULES are similar to class instances and like orphan instances, orphan rules are a bad idea.

It still doesn’t solve the problem quite like adding mapM_ does. Rules aren’t documented anywhere; why would the programmer expect `mapM_ . unpack` to fuse? Moreover, it violates the existing structure of bytestring package. For instance, functions like `last` and `maximum` could be implemented as rules in the same way, but they’re included in Data.ByteString (for good, I’d say).