Discussion:
Generalizing some type signatures involving Int
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Vanessa McHale
2018-11-14 01:18:58 UTC
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Permalink
Would it be possible to generalize replicate and length to have type
signatures

replicate :: Integral a => a -> b -> [b]

and

length :: (Integral a, Foldable t) => t b -> a

?

There have been a few instances where such a thing would have been
useful to me.

Cheers
Alexandre Rodrigues
2018-11-14 01:34:33 UTC
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:+1: from me.



________________________________
From: Libraries <libraries-***@haskell.org> on behalf of Vanessa McHale <***@iohk.io>
Sent: Wednesday, November 14, 2018 1:18:58 AM
To: Haskell Libraries
Subject: Generalizing some type signatures involving Int

Would it be possible to generalize replicate and length to have type
signatures

replicate :: Integral a => a -> b -> [b]

and

length :: (Integral a, Foldable t) => t b -> a

?

There have been a few instances where such a thing would have been
useful to me.

Cheers
Eric Mertens
2018-11-14 02:49:01 UTC
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Permalink
Int is the right type to be able to do efficient internal operations when
implementing length and replicate. It's unlikely that someone would want to
run these operations on another type internally than Int. Some times people
propose types like these where they imagine just a built-in use of
fromIntegral on either the initial argument or the result, but that really
quite unnecessary. Could you elaborate on what cases you had in mind?

While genericLength exists, I have yet to see a good use of it.

Best regards,
Eric Mertens
glguy

On Tue, Nov 13, 2018 at 5:34 PM Alexandre Rodrigues <
***@outlook.com> wrote:

> :+1: from me.
>
>
> ------------------------------
> *From:* Libraries <libraries-***@haskell.org> on behalf of Vanessa
> McHale <***@iohk.io>
> *Sent:* Wednesday, November 14, 2018 1:18:58 AM
> *To:* Haskell Libraries
> *Subject:* Generalizing some type signatures involving Int
>
> Would it be possible to generalize replicate and length to have type
> signatures
>
> replicate :: Integral a => a -> b -> [b]
>
> and
>
> length :: (Integral a, Foldable t) => t b -> a
>
> ?
>
> There have been a few instances where such a thing would have been
> useful to me.
>
> Cheers
>
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>


--
Eric Mertens
Vanessa McHale
2018-11-14 03:19:33 UTC
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Permalink
I certainly do! What's wrong with iterating over a Word?

On 11/13/18 8:49 PM, Eric Mertens wrote:
> Int is the right type to be able to do efficient internal operations
> when implementing length and replicate. It's unlikely that someone
> would want to run these operations on another type internally than
> Int. Some times people propose types like these where they imagine
> just a built-in use of fromIntegral on either the initial argument or
> the result, but that really quite unnecessary. Could you elaborate on
> what cases you had in mind?
>
> While genericLength exists, I have yet to see a good use of it.
>
> Best regards,
> Eric Mertens
> glguy
>
> On Tue, Nov 13, 2018 at 5:34 PM Alexandre Rodrigues
> <***@outlook.com <mailto:***@outlook.com>> wrote:
>
> :+1: from me.
>
>  
>
> ------------------------------------------------------------------------
> *From:* Libraries <libraries-***@haskell.org
> <mailto:libraries-***@haskell.org>> on behalf of Vanessa
> McHale <***@iohk.io <mailto:***@iohk.io>>
> *Sent:* Wednesday, November 14, 2018 1:18:58 AM
> *To:* Haskell Libraries
> *Subject:* Generalizing some type signatures involving Int
>  
> Would it be possible to generalize replicate and length to have type
> signatures
>
> replicate :: Integral a => a -> b -> [b]
>
> and
>
> length :: (Integral a, Foldable t) => t b -> a
>
> ?
>
> There have been a few instances where such a thing would have been
> useful to me.
>
> Cheers
>
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org <mailto:***@haskell.org>
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
>
>
> --
> Eric Mertens
Evan Laforge
2018-11-14 02:50:34 UTC
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Permalink
You can already get these as Data.List.genericLength and
Data.List.genericReplicate

As for changing the prelude ones, this would probably cause a lot of
busywork. Where I work we compile with -Werror and -Wtype-defaults,
so a lot of places might have to get type annotations.
On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io> wrote:
>
> Would it be possible to generalize replicate and length to have type
> signatures
>
> replicate :: Integral a => a -> b -> [b]
>
> and
>
> length :: (Integral a, Foldable t) => t b -> a
>
> ?
>
> There have been a few instances where such a thing would have been
> useful to me.
>
> Cheers
>
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
David Feuer
2018-11-14 03:13:50 UTC
Reply
Permalink
genericLength is extremely inefficient for typical numeric types. Int is a
rather sad type for these things; it really should be Word. But that may
not be worth fixing.

On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com wrote:

> You can already get these as Data.List.genericLength and
> Data.List.genericReplicate
>
> As for changing the prelude ones, this would probably cause a lot of
> busywork. Where I work we compile with -Werror and -Wtype-defaults,
> so a lot of places might have to get type annotations.
> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io>
> wrote:
> >
> > Would it be possible to generalize replicate and length to have type
> > signatures
> >
> > replicate :: Integral a => a -> b -> [b]
> >
> > and
> >
> > length :: (Integral a, Foldable t) => t b -> a
> >
> > ?
> >
> > There have been a few instances where such a thing would have been
> > useful to me.
> >
> > Cheers
> >
> >
> > _______________________________________________
> > Libraries mailing list
> > ***@haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
Vanessa McHale
2018-11-14 03:24:11 UTC
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Permalink
This is perhaps not the right place, but if there are benchmarks proving
that genericLength is slower than it should be, it should be easy to add
a SPECIALIZE pragma.

On 11/13/18 9:13 PM, David Feuer wrote:
> genericLength is extremely inefficient for typical numeric types. Int
> is a rather sad type for these things; it really should be Word. But
> that may not be worth fixing.
>
> On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com
> <mailto:***@gmail.com> wrote:
>
> You can already get these as Data.List.genericLength and
> Data.List.genericReplicate
>
> As for changing the prelude ones, this would probably cause a lot of
> busywork.  Where I work we compile with -Werror and -Wtype-defaults,
> so a lot of places might have to get type annotations.
> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale
> <***@iohk.io <mailto:***@iohk.io>> wrote:
> >
> > Would it be possible to generalize replicate and length to have type
> > signatures
> >
> > replicate :: Integral a => a -> b -> [b]
> >
> > and
> >
> > length :: (Integral a, Foldable t) => t b -> a
> >
> > ?
> >
> > There have been a few instances where such a thing would have been
> > useful to me.
> >
> > Cheers
> >
> >
> > _______________________________________________
> > Libraries mailing list
> > ***@haskell.org <mailto:***@haskell.org>
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
> _______________________________________________
> Libraries mailing list
> ***@haskell.org <mailto:***@haskell.org>
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
David Feuer
2018-11-14 03:30:38 UTC
Reply
Permalink
That won't help whatsoever in most cases. The matter has been discussed
several times with no progress. If you want to add RULES for Int8, Int16,
..., Word, Word8, ..., and Natural to match the ones for Int and Integer,
that would make sense, but the basic problem will remain for unmentioned
types.

On Tue, Nov 13, 2018, 10:24 PM Vanessa McHale <***@iohk.io wrote:

> This is perhaps not the right place, but if there are benchmarks proving
> that genericLength is slower than it should be, it should be easy to add a
> SPECIALIZE pragma.
> On 11/13/18 9:13 PM, David Feuer wrote:
>
> genericLength is extremely inefficient for typical numeric types. Int is a
> rather sad type for these things; it really should be Word. But that may
> not be worth fixing.
>
> On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com wrote:
>
>> You can already get these as Data.List.genericLength and
>> Data.List.genericReplicate
>>
>> As for changing the prelude ones, this would probably cause a lot of
>> busywork. Where I work we compile with -Werror and -Wtype-defaults,
>> so a lot of places might have to get type annotations.
>> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io>
>> wrote:
>> >
>> > Would it be possible to generalize replicate and length to have type
>> > signatures
>> >
>> > replicate :: Integral a => a -> b -> [b]
>> >
>> > and
>> >
>> > length :: (Integral a, Foldable t) => t b -> a
>> >
>> > ?
>> >
>> > There have been a few instances where such a thing would have been
>> > useful to me.
>> >
>> > Cheers
>> >
>> >
>> > _______________________________________________
>> > Libraries mailing list
>> > ***@haskell.org
>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>> _______________________________________________
>> Libraries mailing list
>> ***@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>
>
Alexandre Rodrigues
2018-11-14 18:04:25 UTC
Reply
Permalink
I spoke too soon, I failed to consider that such a proposal must have been under consideration many times before, and there must have been a good reason for it to not to move forward.

Adding RULES for the most commonly used integer types is probably a good place to start, but perhaps I am mistaken.

________________________________
From: Libraries <libraries-***@haskell.org> on behalf of David Feuer <***@gmail.com>
Sent: Wednesday, November 14, 2018 3:30:38 AM
To: Vanessa McHale
Cc: Haskell Libraries
Subject: Re: Generalizing some type signatures involving Int

That won't help whatsoever in most cases. The matter has been discussed several times with no progress. If you want to add RULES for Int8, Int16, ..., Word, Word8, ..., and Natural to match the ones for Int and Integer, that would make sense, but the basic problem will remain for unmentioned types.

On Tue, Nov 13, 2018, 10:24 PM Vanessa McHale <***@iohk.io<mailto:***@iohk.io> wrote:

This is perhaps not the right place, but if there are benchmarks proving that genericLength is slower than it should be, it should be easy to add a SPECIALIZE pragma.

On 11/13/18 9:13 PM, David Feuer wrote:
genericLength is extremely inefficient for typical numeric types. Int is a rather sad type for these things; it really should be Word. But that may not be worth fixing.

On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com<mailto:***@gmail.com> wrote:
You can already get these as Data.List.genericLength and
Data.List.genericReplicate

As for changing the prelude ones, this would probably cause a lot of
busywork. Where I work we compile with -Werror and -Wtype-defaults,
so a lot of places might have to get type annotations.
On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io<mailto:***@iohk.io>> wrote:
>
> Would it be possible to generalize replicate and length to have type
> signatures
>
> replicate :: Integral a => a -> b -> [b]
>
> and
>
> length :: (Integral a, Foldable t) => t b -> a
>
> ?
>
> There have been a few instances where such a thing would have been
> useful to me.
>
> Cheers
>
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org<mailto:***@haskell.org>
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Carter Schonwald
2018-11-15 06:30:19 UTC
Reply
Permalink
Agreed.

As David and Eric both say:
For in heap / memory size structures, it’s impossible to ever have an in
ram structure that exceeds the largest positive value for Int. And ghc is
also quite good at optimizing int.

1) what is your application domain / context ?

2) all of these are implementable in user space, what design /
implementation experiments have you done ?

It’s worth mentioning that RULES style optimization in this case would only
run AFTER it’s been specialized to a concrete type. And that short of lots
of specialize pragmas or inlining , the generic code will thusly miss out
on all sorts of unboxong etc.

On Tue, Nov 13, 2018 at 10:31 PM David Feuer <***@gmail.com> wrote:

> That won't help whatsoever in most cases. The matter has been discussed
> several times with no progress. If you want to add RULES for Int8, Int16,
> ..., Word, Word8, ..., and Natural to match the ones for Int and Integer,
> that would make sense, but the basic problem will remain for unmentioned
> types.
>
> On Tue, Nov 13, 2018, 10:24 PM Vanessa McHale <***@iohk.io
> wrote:
>
>> This is perhaps not the right place, but if there are benchmarks proving
>> that genericLength is slower than it should be, it should be easy to add a
>> SPECIALIZE pragma.
>> On 11/13/18 9:13 PM, David Feuer wrote:
>>
>> genericLength is extremely inefficient for typical numeric types. Int is
>> a rather sad type for these things; it really should be Word. But that may
>> not be worth fixing.
>>
>> On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com wrote:
>>
>>> You can already get these as Data.List.genericLength and
>>> Data.List.genericReplicate
>>>
>>> As for changing the prelude ones, this would probably cause a lot of
>>> busywork. Where I work we compile with -Werror and -Wtype-defaults,
>>> so a lot of places might have to get type annotations.
>>> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io>
>>> wrote:
>>> >
>>> > Would it be possible to generalize replicate and length to have type
>>> > signatures
>>> >
>>> > replicate :: Integral a => a -> b -> [b]
>>> >
>>> > and
>>> >
>>> > length :: (Integral a, Foldable t) => t b -> a
>>> >
>>> > ?
>>> >
>>> > There have been a few instances where such a thing would have been
>>> > useful to me.
>>> >
>>> > Cheers
>>> >
>>> >
>>> > _______________________________________________
>>> > Libraries mailing list
>>> > ***@haskell.org
>>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>> _______________________________________________
>>> Libraries mailing list
>>> ***@haskell.org
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>>
>> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
Zemyla
2018-11-15 22:57:46 UTC
Reply
Permalink
It's not actually impossible to have an in RAM structure that exceeds
the largest positive value for Int. Data.Sequence.replicate does it by
exploiting sharing. replicate n a uses O(lg n) space.

> length $ let x = Data.Sequence.Replicate maxBound 'a' :> 'b' in mappend x x
0

Also, I really would like to have all the length and count-based
functions in base, containers, etc. take or return Words, but there's
way too much inertia behind Ints, even if it means you have to check
for negative numbers (which really runs counter to the main thesis
behind Haskell; i.e. have your types say what you mean).

On Thu, Nov 15, 2018 at 12:30 AM Carter Schonwald
<***@gmail.com> wrote:
>
> Agreed.
>
> As David and Eric both say:
> For in heap / memory size structures, it’s impossible to ever have an in ram structure that exceeds the largest positive value for Int. And ghc is also quite good at optimizing int.
>
> 1) what is your application domain / context ?
>
> 2) all of these are implementable in user space, what design / implementation experiments have you done ?
>
> It’s worth mentioning that RULES style optimization in this case would only run AFTER it’s been specialized to a concrete type. And that short of lots of specialize pragmas or inlining , the generic code will thusly miss out on all sorts of unboxong etc.
>
> On Tue, Nov 13, 2018 at 10:31 PM David Feuer <***@gmail.com> wrote:
>>
>> That won't help whatsoever in most cases. The matter has been discussed several times with no progress. If you want to add RULES for Int8, Int16, ..., Word, Word8, ..., and Natural to match the ones for Int and Integer, that would make sense, but the basic problem will remain for unmentioned types.
>>
>> On Tue, Nov 13, 2018, 10:24 PM Vanessa McHale <***@iohk.io wrote:
>>>
>>> This is perhaps not the right place, but if there are benchmarks proving that genericLength is slower than it should be, it should be easy to add a SPECIALIZE pragma.
>>>
>>> On 11/13/18 9:13 PM, David Feuer wrote:
>>>
>>> genericLength is extremely inefficient for typical numeric types. Int is a rather sad type for these things; it really should be Word. But that may not be worth fixing.
>>>
>>> On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com wrote:
>>>>
>>>> You can already get these as Data.List.genericLength and
>>>> Data.List.genericReplicate
>>>>
>>>> As for changing the prelude ones, this would probably cause a lot of
>>>> busywork. Where I work we compile with -Werror and -Wtype-defaults,
>>>> so a lot of places might have to get type annotations.
>>>> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io> wrote:
>>>> >
>>>> > Would it be possible to generalize replicate and length to have type
>>>> > signatures
>>>> >
>>>> > replicate :: Integral a => a -> b -> [b]
>>>> >
>>>> > and
>>>> >
>>>> > length :: (Integral a, Foldable t) => t b -> a
>>>> >
>>>> > ?
>>>> >
>>>> > There have been a few instances where such a thing would have been
>>>> > useful to me.
>>>> >
>>>> > Cheers
>>>> >
>>>> >
>>>> > _______________________________________________
>>>> > Libraries mailing list
>>>> > ***@haskell.org
>>>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>>> _______________________________________________
>>>> Libraries mailing list
>>>> ***@haskell.org
>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>
>> _______________________________________________
>> Libraries mailing list
>> ***@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
Henning Thielemann
2018-11-15 23:18:41 UTC
Reply
Permalink
On Thu, 15 Nov 2018, Zemyla wrote:

> It's not actually impossible to have an in RAM structure that exceeds
> the largest positive value for Int. Data.Sequence.replicate does it by
> exploiting sharing. replicate n a uses O(lg n) space.
>
>> length $ let x = Data.Sequence.Replicate maxBound 'a' :> 'b' in mappend x x
> 0

One could also imagine a data structure like Multiset/Bag, where every
element has a count and 'length' returns the total count.

> Also, I really would like to have all the length and count-based
> functions in base, containers, etc. take or return Words, but there's
> way too much inertia behind Ints, even if it means you have to check
> for negative numbers (which really runs counter to the main thesis
> behind Haskell; i.e. have your types say what you mean).

We would also need a bound-checked counterpart to Word. Currently,
(-1)::Word or (2-3)::Word is accepted without a runtime error.
Consequently, 'newTake (-1) xs' would likely return the full list xs.
David Feuer
2018-11-16 02:48:40 UTC
Reply
Permalink
Data.Sequence actually doesn't support anything outside the Int range. It
could, at a small cost. We perform some range checks cheaply using unsigned
comparisons. We'd have to stop doing that to allow sequences to be just a
tad more absurdly large. Since that's not often useful, sequences are
currently limited to lengths of maxBound @Int.

On Thu, Nov 15, 2018, 5:53 PM Zemyla <***@gmail.com wrote:

> It's not actually impossible to have an in RAM structure that exceeds
> the largest positive value for Int. Data.Sequence.replicate does it by
> exploiting sharing. replicate n a uses O(lg n) space.
>
> > length $ let x = Data.Sequence.Replicate maxBound 'a' :> 'b' in mappend
> x x
> 0
>
> Also, I really would like to have all the length and count-based
> functions in base, containers, etc. take or return Words, but there's
> way too much inertia behind Ints, even if it means you have to check
> for negative numbers (which really runs counter to the main thesis
> behind Haskell; i.e. have your types say what you mean).
>
> On Thu, Nov 15, 2018 at 12:30 AM Carter Schonwald
> <***@gmail.com> wrote:
> >
> > Agreed.
> >
> > As David and Eric both say:
> > For in heap / memory size structures, it’s impossible to ever have an in
> ram structure that exceeds the largest positive value for Int. And ghc is
> also quite good at optimizing int.
> >
> > 1) what is your application domain / context ?
> >
> > 2) all of these are implementable in user space, what design /
> implementation experiments have you done ?
> >
> > It’s worth mentioning that RULES style optimization in this case would
> only run AFTER it’s been specialized to a concrete type. And that short of
> lots of specialize pragmas or inlining , the generic code will thusly miss
> out on all sorts of unboxong etc.
> >
> > On Tue, Nov 13, 2018 at 10:31 PM David Feuer <***@gmail.com>
> wrote:
> >>
> >> That won't help whatsoever in most cases. The matter has been discussed
> several times with no progress. If you want to add RULES for Int8, Int16,
> ..., Word, Word8, ..., and Natural to match the ones for Int and Integer,
> that would make sense, but the basic problem will remain for unmentioned
> types.
> >>
> >> On Tue, Nov 13, 2018, 10:24 PM Vanessa McHale <***@iohk.io
> wrote:
> >>>
> >>> This is perhaps not the right place, but if there are benchmarks
> proving that genericLength is slower than it should be, it should be easy
> to add a SPECIALIZE pragma.
> >>>
> >>> On 11/13/18 9:13 PM, David Feuer wrote:
> >>>
> >>> genericLength is extremely inefficient for typical numeric types. Int
> is a rather sad type for these things; it really should be Word. But that
> may not be worth fixing.
> >>>
> >>> On Tue, Nov 13, 2018, 9:51 PM Evan Laforge <***@gmail.com wrote:
> >>>>
> >>>> You can already get these as Data.List.genericLength and
> >>>> Data.List.genericReplicate
> >>>>
> >>>> As for changing the prelude ones, this would probably cause a lot of
> >>>> busywork. Where I work we compile with -Werror and -Wtype-defaults,
> >>>> so a lot of places might have to get type annotations.
> >>>> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <
> ***@iohk.io> wrote:
> >>>> >
> >>>> > Would it be possible to generalize replicate and length to have type
> >>>> > signatures
> >>>> >
> >>>> > replicate :: Integral a => a -> b -> [b]
> >>>> >
> >>>> > and
> >>>> >
> >>>> > length :: (Integral a, Foldable t) => t b -> a
> >>>> >
> >>>> > ?
> >>>> >
> >>>> > There have been a few instances where such a thing would have been
> >>>> > useful to me.
> >>>> >
> >>>> > Cheers
> >>>> >
> >>>> >
> >>>> > _______________________________________________
> >>>> > Libraries mailing list
> >>>> > ***@haskell.org
> >>>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
> >>>> _______________________________________________
> >>>> Libraries mailing list
> >>>> ***@haskell.org
> >>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
> >>
> >> _______________________________________________
> >> Libraries mailing list
> >> ***@haskell.org
> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
> >
> > _______________________________________________
> > Libraries mailing list
> > ***@haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
Vanessa McHale
2018-11-14 03:21:04 UTC
Reply
Permalink
Thanks! This is a decent stopgap.

On 11/13/18 8:50 PM, Evan Laforge wrote:
> You can already get these as Data.List.genericLength and
> Data.List.genericReplicate
>
> As for changing the prelude ones, this would probably cause a lot of
> busywork. Where I work we compile with -Werror and -Wtype-defaults,
> so a lot of places might have to get type annotations.
> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io> wrote:
>> Would it be possible to generalize replicate and length to have type
>> signatures
>>
>> replicate :: Integral a => a -> b -> [b]
>>
>> and
>>
>> length :: (Integral a, Foldable t) => t b -> a
>>
>> ?
>>
>> There have been a few instances where such a thing would have been
>> useful to me.
>>
>> Cheers
>>
>>
>> _______________________________________________
>> Libraries mailing list
>> ***@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
David Feuer
2018-11-14 03:22:42 UTC
Reply
Permalink
No, genericLength is *not* a decent stopgap. It's horrible. Just look at
the implementation!

On Tue, Nov 13, 2018, 10:21 PM Vanessa McHale <***@iohk.io wrote:

> Thanks! This is a decent stopgap.
>
> On 11/13/18 8:50 PM, Evan Laforge wrote:
> > You can already get these as Data.List.genericLength and
> > Data.List.genericReplicate
> >
> > As for changing the prelude ones, this would probably cause a lot of
> > busywork. Where I work we compile with -Werror and -Wtype-defaults,
> > so a lot of places might have to get type annotations.
> > On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io>
> wrote:
> >> Would it be possible to generalize replicate and length to have type
> >> signatures
> >>
> >> replicate :: Integral a => a -> b -> [b]
> >>
> >> and
> >>
> >> length :: (Integral a, Foldable t) => t b -> a
> >>
> >> ?
> >>
> >> There have been a few instances where such a thing would have been
> >> useful to me.
> >>
> >> Cheers
> >>
> >>
> >> _______________________________________________
> >> Libraries mailing list
> >> ***@haskell.org
> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
Henning Thielemann
2018-11-15 18:39:13 UTC
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On Tue, 13 Nov 2018, David Feuer wrote:

> No, genericLength is *not* a decent stopgap. It's horrible. Just look at
> the implementation!

It looks like it is intended to return something like a lazy Peano number.
David Feuer
2018-11-15 19:28:28 UTC
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That is precisely correct. And I have heard that it has actually been
used that way ... once. It's not exactly a common application.
On Thu, Nov 15, 2018 at 1:39 PM Henning Thielemann
<***@henning-thielemann.de> wrote:
>
>
> On Tue, 13 Nov 2018, David Feuer wrote:
>
> > No, genericLength is *not* a decent stopgap. It's horrible. Just look at
> > the implementation!
>
> It looks like it is intended to return something like a lazy Peano number.
Vanessa McHale
2018-11-14 03:22:53 UTC
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Permalink
I want more than this, actually. genericLength doesn't work over any
Foldable.

On 11/13/18 8:50 PM, Evan Laforge wrote:
> You can already get these as Data.List.genericLength and
> Data.List.genericReplicate
>
> As for changing the prelude ones, this would probably cause a lot of
> busywork. Where I work we compile with -Werror and -Wtype-defaults,
> so a lot of places might have to get type annotations.
> On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io> wrote:
>> Would it be possible to generalize replicate and length to have type
>> signatures
>>
>> replicate :: Integral a => a -> b -> [b]
>>
>> and
>>
>> length :: (Integral a, Foldable t) => t b -> a
>>
>> ?
>>
>> There have been a few instances where such a thing would have been
>> useful to me.
>>
>> Cheers
>>
>>
>> _______________________________________________
>> Libraries mailing list
>> ***@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
David Feuer
2018-11-14 03:25:41 UTC
Reply
Permalink
You still haven't said why you need this. Only a rather exotic data
structure is likely to have a length greater than maxBound @Int.

On Tue, Nov 13, 2018, 10:23 PM Vanessa McHale <***@iohk.io wrote:

> I want more than this, actually. genericLength doesn't work over any
> Foldable.
>
> On 11/13/18 8:50 PM, Evan Laforge wrote:
> > You can already get these as Data.List.genericLength and
> > Data.List.genericReplicate
> >
> > As for changing the prelude ones, this would probably cause a lot of
> > busywork. Where I work we compile with -Werror and -Wtype-defaults,
> > so a lot of places might have to get type annotations.
> > On Tue, Nov 13, 2018 at 5:19 PM Vanessa McHale <***@iohk.io>
> wrote:
> >> Would it be possible to generalize replicate and length to have type
> >> signatures
> >>
> >> replicate :: Integral a => a -> b -> [b]
> >>
> >> and
> >>
> >> length :: (Integral a, Foldable t) => t b -> a
> >>
> >> ?
> >>
> >> There have been a few instances where such a thing would have been
> >> useful to me.
> >>
> >> Cheers
> >>
> >>
> >> _______________________________________________
> >> Libraries mailing list
> >> ***@haskell.org
> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
> _______________________________________________
> Libraries mailing list
> ***@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
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