Generalize IsString

Dannyu NDos

6 Jun 2020 6 Jun '20

2:11 a.m.

As we already have IsList, shouldn't we just do this? class (IsList l, Item l ~ Char) => IsString l instance (a ~ Char) => IsString [a] instance (a ~ Char) => IsString (NonEmpty a) instance (a ~ Char) => IsString (ZipList a)

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chessai .

6 Jun 6 Jun

2:24 a.m.

This would require desugaring string literals using `fromListN`, which would require GHC effort. Also, consider ByteString. Is `Item ByteString` `Word8` or `Char`? Additionally, I'm not convinced this coupling really buys us much. You could always define `fromString = fromList`. On Fri, Jun 5, 2020, 11:12 PM Dannyu NDos wrote:

...

As we already have IsList, shouldn't we just do this?

class (IsList l, Item l ~ Char) => IsString l

instance (a ~ Char) => IsString [a] instance (a ~ Char) => IsString (NonEmpty a) instance (a ~ Char) => IsString (ZipList a) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Zemyla

7:12 a.m.

There are some things which I've seen with IsString instances which can't have toList applied to them, like parsers. On Sat, Jun 6, 2020, 01:25 chessai . wrote:

...

This would require desugaring string literals using `fromListN`, which would require GHC effort.

Also, consider ByteString. Is `Item ByteString` `Word8` or `Char`?

Additionally, I'm not convinced this coupling really buys us much. You could always define `fromString = fromList`.

On Fri, Jun 5, 2020, 11:12 PM Dannyu NDos wrote:

...
As we already have IsList, shouldn't we just do this?

class (IsList l, Item l ~ Char) => IsString l

instance (a ~ Char) => IsString [a] instance (a ~ Char) => IsString (NonEmpty a) instance (a ~ Char) => IsString (ZipList a) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

chessai .

11:52 a.m.

Ah, good point Zemyla. Also HtmlT, from Lucid. On Sat, Jun 6, 2020, 4:12 AM Zemyla wrote:

...

There are some things which I've seen with IsString instances which can't have toList applied to them, like parsers.

On Sat, Jun 6, 2020, 01:25 chessai . wrote:

...
This would require desugaring string literals using `fromListN`, which would require GHC effort.

Also, consider ByteString. Is `Item ByteString` `Word8` or `Char`?

Additionally, I'm not convinced this coupling really buys us much. You could always define `fromString = fromList`.

On Fri, Jun 5, 2020, 11:12 PM Dannyu NDos wrote:

...
As we already have IsList, shouldn't we just do this?

class (IsList l, Item l ~ Char) => IsString l

instance (a ~ Char) => IsString [a] instance (a ~ Char) => IsString (NonEmpty a) instance (a ~ Char) => IsString (ZipList a) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Mario

7 Jun 7 Jun

5:38 p.m.

On 2020-06-06 2:11 a.m., Dannyu NDos wrote:

...

As we already have IsList, shouldn't we just do this?

class(IsListl, Iteml~Char) => IsStringl instance(a~Char) => IsString[a] instance(a~Char) => IsString(NonEmptya) instance(a~Char) => IsString(ZipLista)

That's not a generalization, it's a restriction. It would, for example, exclude both ByteString (whose IsString instance is admittedly broken) and ByteStringUTF8 (whose isn't).

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chessai .
Dannyu NDos
Mario
Zemyla