February 2019 - Libraries

Deprecating fromIntegral
by Niklas Hambüchen 12 Aug '20

12 Aug '20

This is not a joke. I just found a bug in base (https://ghc.haskell.org/trac/ghc/ticket/14262) import System.IO hWaitForInput stdin 4294968296 This code should wait for 49.something days, but it waits for 1 second. It is caused by a quick use of `fromIntegral` to "convert" `Int -> CInt` (where CInt = Int32), causing an overflow. I argue that `fromIntegral` causes unnoticed data corruption without any warning, and thus are worse than partial functions. In this case, this data corruption occurs in the most fundamental code that we all use and have to rely upon (`base`). So I propose that we add a deprecation pragma to `fromIntegral` (however, keeping it forever, like Java does, as there's no benefit to removing it, we just want that people use safer functions over time), and instead provide a `safeFromIntegral` that can only widen ranges, and one or more `unsafeFromIntegral` or appropriately named functions that can error, wrap, return Maybe, or have whatever desired behaviour when the input value doesn't fit into the output type. For some inspiration, `foundation` provides ideas in that direction: http://hackage.haskell.org/package/basement-0.0.2/docs/Basement-From.html http://hackage.haskell.org/package/basement-0.0.2/docs/Basement-IntegralCon… It is a bit funny how we argue that Haskell is good for high assurance programming, and we build all sorts of fancy constructs to eliminate more run-time errors, when in fact we do worse than C in detecting errors in the most basic types a computer can use, such as converting between 64-bit and 32-bit integers. Let's fix that. It avoids real problems in real production systems that are difficult to debug when they happen (who writes a unit test checking that a timeout of 50 days still works? This is the kind of stuff where you have to rely on -- very basic -- types). I'd like to probe support for such a change before doing any work on it. Niklas

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Deprecate First and Last in Data.Monoid
by Andrew Martin 13 Jun '20

13 Jun '20

I propose that the data types First and Last, provided by Data.Monoid, be marked deprecated in GHC 8.6 and removed in GHC 8.10. The Semigroup-Monoid Proposal (SMP) brought about changes that, I will argue, make these data types (1) unneeded and (2) confusing. Why are they no longer needed? Data.Semigroup provides two identically named data types (First and Last). These have Semigroup instances matches what their names suggest. Additionally, SMP corrects the Monoid instance for Maybe so that it now lifts Semigroup instances instead of Monoid instances. What this means is that, assuming the following imports: import qualified Data.Monoid as M import qualified Data.Semigroup as S We have the following equivalences: M.First a === Maybe (M.First a) M.Last a === Maybe (M.Last a) When I say "equivalence", I mean that their Monoid instances have the same behavior. Their Show/Read instances are certainly different, and I’m not sure about their Ord instances. Getting back to the second reason, removing these data types would eliminate confusion. It’s strange that Semigroup is a superclass of Monoid, yet they have Data types with conflicting names defined in their respective modules. When you see the data type First, you cannot tell what someone is talking additional context. In general, base strives to avoid duplicate identifiers. The only other exception to this rule I can think of is that Bifunctor and Arrow both use the identifiers first and second. But, the situation with Data.Semigroup and Data.Monoid is higher impact since people are more likely to import these modules unqualified together. (As an aside, and the confusion I’m talking about here isn’t entirely hypothetical. I got tripped up by this when I first started using the semigroups library. I had to train myself to stop importing Data.Monoid unqualified, because it kept stealing these identifiers) Again, the two reasons are that these are no longer necessary and that they cause confusion. I would appreciate any feedback, including simple nods of agreement or disagreement. Thanks. -- -Andrew Thaddeus Martin

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Incremental Regex Parsing with Fixed Strings
by Andrew Martin 12 Sep '19

12 Sep '19

Greetings, In Dan Piponi's blog post Fast Incremental Regular Expression Matching with Monoids [1], he outlines a way to take advantage of fingertrees to perform increment regex matching. In his article, the regular expression (more accurately, its equivalent DFA) is fixed, and the strings we are matching on are modified incrementally. What I'm interested in is the opposite: What if the regular expression is modified incrementally and the string we are testing is static? Thinking about this, it seems to run into problems immediately. Typically, to evaluate a regular expression, I would convert it to a NFA (and then maybe to a DFA). But there is no way to do incremental graph modification on the resulting graphs. (Or is there?). And even if there were a way, it seems unclear how one would go about exploiting its incremental nature. To provide an example, consider the following regex and sample string: Regex: Lost (dog|cat) loo for home Sample: Lost dog looking for home In the regex, I'm currently in the middle of typing "looking", so it doesn't match the sample string. But large parts of it do. So when I update the regex by typing "k", I'd like to be able to not redo this work. Maybe there's a certain subset of regex that's amenable to this kind of incremental evaluation. Maybe not. If anyone has any additional insights or can point me to any research, I would appreciate it greatly. Thanks. [1] http://blog.sigfpe.com/2009/01/fast-incremental-regular-expression.html -- -Andrew Thaddeus Martin

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Add 'e' to Floating typeclass
by chessai . 22 Feb '19

22 Feb '19

We have the 'pi' constant in the floating typeclass and some trigonometric functions, as well as things like exp/log/expm1/log1p. Why not provide an 'e' constant? A default implementation could just be 'exp 1'.

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Add newtype for Alternative using QuantifiedConstraints in base-4.13
by theindigamer 19 Feb '19

19 Feb '19

Thoughts on adding a newtype with the following Alternative instance? (The name chosen is a placeholder, I don't have any particular preference). newtype Mon f a = Mon { unMon :: f a } instance (forall a. Monoid (f a)) => Alternative (Mon f) where empty = Mon mempty (<|>) (Mon m1) (Mon m2) = Mon (m1 <> m2)

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ANNOUNCE: eccrypto 0.1.0, timing attack safe cryptography in Haskell
by Marcel Fourné 19 Feb '19

19 Feb '19

Dear Haskell Community! I'd like to introduce some new cryptographic code, containing a verified[*] timing-attack safe pure Haskell[**] implementation of Ed25519 and as of yet unverified implementations of textbook ECDH and ECDSA on the NIST prime curves. Install it by $ cabal install eccrypto or download it from Hackage[0]. Also contained are test vectors, usable by the trusty $ cabal test as well as benchmarking code which you can invoke by $ cabal bench if you want to try my code before using it. Please note that this is a one person project, so there is still much room for optimization. The intended focus groups are implementors of cryptographic protocols as well as other cryptographers and interested third parties. My code uses no[**] embedded C code or assembly to achieve timing attack resistance, only careful Haskell constructions in the internal modules, the obligatory hackers footgun included only in those. ;-) Security sketch: The timing attack safety is built on the constant time criterion, namely, that no branches or memory access indices may be based on the content of the secret key bits. The name of this criterion is from the strict evaluation world of cryptography, but does not prohibit non-strict evaluation semantics per se. The API is only slightly different from contemporary libraries like "ed25519"[1], but the content of the signatures is just the same. The number of dependencies are also in the same ballpark, if you'd like to use the code for infrastructure - but in that case, please talk to me to not use unverified/insecure operations! Best of wishes to a thriving community, Marcel Fourné [*]: paper upcoming but as of now it only exists in my notes; analysis was done "by hand" on assembly generated by GHC 8.4.4, mechanization based on established proofs is planned [**]: using integer-gmp, might change in the future to low-level Haskell [0]: https://hackage.haskell.org/package/eccrypto-0.1.0 [1]: https://hackage.haskell.org/package/ed25519

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Fwd: Add newtype for Alternative using QuantifiedConstraints in base-4.13
by Ruben Astudillo 17 Feb '19

17 Feb '19

Forwarding the replies sent incorrectly to -cafe. -------- Forwarded Message -------- Subject: Re: Add newtype for Alternative using QuantifiedConstraints in base-4.13 Date: Sun, 17 Feb 2019 21:05:12 -0300 From: Ruben Astudillo <ruben.astud(a)gmail.com> To: theindigamer <theindigamer15(a)gmail.com>, Haskell Cafe <haskell-cafe(a)haskell.org> I wonder if it is useful at all. If `f a` already has a Monoid instance, you can use `(<>)` already instead of (<|>) with pretty much the same laws. Plus you don't have to import `(<>)` as it comes from the Prelude where `(<|>)` doesn't. Does this have an use case or is just for aesthetic completeness? -- -- Ruben -- pgp: 4EE9 28F7 932E F4AD

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Taking over haskell-src-meta
by Dan Burton 11 Feb '19

11 Feb '19

I, Dan Burton, intend to take over maintenance of haskell-src-meta. -- Dan Burton

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add map back to Functor
by Carter Schonwald 11 Feb '19

11 Feb '19

harkening back to the old Haskell 1.5 days, Lets have map back in functor. it "F"- strange to not have our lovely maps be functorial by default. I think it would be a genuine boon for old and new haskellers alike, and those who disagree with this change already use alt-preludes for pedagogy reasons anyways

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Add Ord Laws to next Haskell Report
by chessai . 11 Feb '19

11 Feb '19

Per GHC.Classes (haddock-viewable from Data.Ord) "The Haskell Report defines no laws for Ord. However, <= is customarily expected to implement a non-strict partial order and have the following properties:" I propose that in the next report that the expected typeclass laws for Ord be added. They're generally agreed upon/understood.

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