Haskell 98 Report

[Simon Peyton-Jones]

| > |   deleteBy :: (a -> b -> Bool) -> a -> [b] -> [b]
| > |=20
| > | I've found it usefully used at this more general type.
| >=20
| > Indeed, and
| >=20
| >    deleteFirstsBy :: (a -> b -> Bool) -> [b] -> [a] -> [b]
|=20
| and
|=20
|      intersectBy :: (a -> b -> Bool) -> [a] -> [b] -> [a]

Indeed.

We should either generalise all three
	deleteBy
	deleteFirstsBy
	intersectBy
or none.

In favour:
	the more general types are occasionally useful
	no programs stop working

Against
	it's an unforced change
	perhaps some error message may get more obscure

Tom wrote
| That suggests a reason to leave the type of intersectBy alone=20
| - the generalisation would arbitrarily favour the first=20
| list's type over the second list's type.  To me, the word=20
| "intersect" implies symmetry.

The point is that you can always use it at the symmetrical type too.



This isn't a big issue, or I would not be considering it at this point.
So I solicit feedback, and will then just decide something.

Simon