monoid | Customisable coding font with alternates , ligatures | User Interface library
kandi X-RAY | monoid Summary
kandi X-RAY | monoid Summary
Customisable coding font with alternates, ligatures and contextual positioning. Crazy crisp at 12px/9pt. http://larsenwork.com/monoid/
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Top functions reviewed by kandi - BETA
- Build a batch
- Build a font
- Generator of all possible permutations
- Expand the list of possible options
- Add style options
- Generate a variation function
- Calculates the bearing between left and right side
- Declare an option
- Create a function to swap two glyphs
- Return a function that drops calt and liga
- Decorator to define a line method
- Resolve conflicting options
monoid Key Features
monoid Examples and Code Snippets
Lines of Code : 33License : Permissive (MIT)
Copystruct PersonData {
let name: String, age: Int, height: Double, weight: Double
}
let records = [
PersonData(name: "Fred", age: 50, height: 170, weight: 65),
PersonData(name: "Jane", age: 50, height: 170, weight: 52),
PersonData(name: "Nora", (Observable.just(1, 2) |+| Observable.just(3, 4)) === Observable.just(1, 2, 3, 4)
(Observable.just(1, 2) ⊹ Observable.just(3, 4)) === Observable.just(1, 2, 3, 4)
mzero[Observable[Int]] === Observable.empty
public interface Monoid extends Semigroup {
T zero();
}
Community Discussions
Trending Discussions on monoid
QUESTION
Haskell typeclasses often come with laws; for instance, instances of Monoid are expected to observe that x <> mempty = mempty <> x = x.
Typeclass laws are often written with single-equals (=) rather than double-equals (==). This suggests that the notion of equality used in typeclass laws is something other than that of Eq (which makes sense, since Eq is not a superclass of Monoid)
Searching around, I was unable to find any authoritative statement on the meaning of = in typeclass laws. For instance:
- The Haskell 2010 report does not even contain the word "law" in it
- Speaking with other Haskell users, most people seem to believe that
=usually means extensional equality or substitution but is fundamentally context-dependent. Nobody provided any authoritative source for this claim. - The Haskell wiki article on monad laws states that
=is extensional, but, again, fails to provide a source, and I wasn't able to track down any way to contact the author of the relevant edit.
The question, then: Is there any authoritative source on or standard for the semantics for = in typeclass laws? If so, what is it? Additionally, are there examples where the intended meaning of = is particularly exotic?
(As a side note, treating = extensionally can get tricky. For instance, there is a Monoid (IO a) instance, but it's not really clear what extensional equality of IO values looks like.)
ANSWER
Answered 2022-Feb-24 at 22:30Typeclass laws are not part of the Haskell language, so they are not subject to the same kind of language-theoretic semantic analysis as the language itself.
Instead, these laws are typically presented as an informal mathematical notation. Most presentations do not need a more detailed mathematical exposition, so they do not provide one.
QUESTION
Given the following data type
...ANSWER
Answered 2022-Feb-21 at 11:18Inspired by this answer, and with the help of the generic-data package one can write:
QUESTION
First time using lens. set and over went easy enough and I thought it would be simple with view: Use the same scheme to reference the inner part, but don't supply a new value or function. But Noooo. tst3 below gives the error below the code. Anyone know what's going on?
ANSWER
Answered 2022-Feb-20 at 23:35ix 0 doesn't produce a lens, but a traversal.1
Informally, a lens is a "path" that will definitively reach a single value (if you follow it within a hypothetical larger value). A traversal is a path to zero or more values. You can set or view the single target of a lens. And you can set the zero or more targets of a traversal (this simply updates all of them that are present, which is a no-op if there are zero present). But viewing the targets of a traversal is less straightforward.
If view simply took a traversal, and an outer structure, and gave you the target value, then it would have a problem. If there are multiple targets, how should it decide which to return? And if there are zero targets, it can't return anything; it would have to be partial. What it needs is a way of condensing zero-or-more values into a single value, so it can return that. And the Monoid class provides exactly the facilities to do that; mempty for if there aren't any targets at all, and <> to condense multiple values to a single one. So view with a traversal2 actually requires a Monoid constraint on the returned type, and that's why you're getting the complaint about No instance for (Monoid Int) arising from a use of `ix'.
And in case it isn't clear, you can often compose (with .) different types of optics (the general term for "lens-ish things", including lenses, traversals, and several others). But the result has the capabilities of the least capable of the two inputs. So even though your inner and w are full lenses, composing them with a traversal produced by ix results in a traversal, not a lens.
But in this case you know that you're using ix. The specific kind of traversals ix makes end up having zero or one target, rather than the zero or more targets that traversals have in general. So you could use preview instead of view; for a traversal it will produce a Maybe containing Just the first target of the traversal, or Nothing if there weren't any. A Maybe is exactly what the type system deems appropriate here, since ix can't guarantee there will be a target value, but there won't be more than one.
In my experience, when I try to view something and get this Monoid instance error, it almost always means I have an optic that can't guarantee a result and I should actually be using preview to get a Maybe.
Simple example:
QUESTION
here is a puzzle that I keep on bumping into and that, I believe, no previous SO question has been addressing: How can I best use the lens library to set or get values within a State monad managing a nested data structure that involves Maps when I know for a fact that certain keys are present in the maps involved?
ANSWER
Answered 2022-Feb-09 at 11:43If you are sure that the key is present then you can use fromJust to turn the Maybe User into a User:
QUESTION
the stack command stack new my-project creates a auto-generated file Setup.hs with contents:
ANSWER
Answered 2022-Jan-16 at 22:48The error means that you have that package installed, but it is not listed as a dependency in your project. You need to add it in the package.yaml in library/dependencies or your exe:
QUESTION
I'm new to Haskell. Concepts such as monad and monoid, and their corresponding typeclasses, are very interesting but highly abstract and distant. I wonder how those advanced concepts can make things easier to implement. Some self-contained concrete examples would be nice to see.
...ANSWER
Answered 2021-Nov-25 at 18:56You get a way of understanding your problem domain in terms of types and type classes. Here is what I can gather from looking at V3 and its instances, without thinking about what the type is used to represent (3D vector).
QUESTION
The laws for monoids in the category of endofunctors are:
And the Haskell monad laws are:
Left identity: return a >>= k = k a
Right identity: m >>= return = m
Associativity: m >>= (\x -> k x >>= h) = (m >>= k) >>= h
I'm assuming the latter is derived from the former, but how so? The diagrams basically say
...ANSWER
Answered 2021-Oct-21 at 20:22Phrase the monad laws in terms of the Kleisli composition operator (>=>).
Assuming k :: a -> m b, k' :: b -> m c, k'' :: c -> m d (i.e. k, k', k'' are Kleisli arrows)
- Left identity:
return >=> k = k - Right identity:
k >=> return = k - Associativity:
(k >=> k') >=> k'' = k >=> (k' >=> k'')
It's relatively straightforward from the definition of (>=>) to show that these are equivalent to what you wrote. And you don't need any fancy diagrams or anything: these are literally the monoid laws, with return as the identity and (>=>) as your monoid operation.
The diagram you show in your picture is a different way of thinking about monads. You can equivalently define monads in terms of natural transformations (i.e. join and return) or in terms of composition (i.e. return and (>>=) / (>=>)). The latter approach lends itself to the monoid way of thinking that you're looking for.
QUESTION
Suppose I would like to write two Typeclasses. Header:
...ANSWER
Answered 2021-Oct-11 at 23:21I think there's a couple reasoning errors going on here at once.
First: when you write
QUESTION
I have an input list of type [Maybe SomeType] and a predicate p of type SomeType -> Bool, and I want to answer the question "Does the predicate p hold for all SomeTypes that happen to be in the input?".
The first part is easy: (map . fmap) p list is of type [Maybe Bool].
One important info is that I know that length list >= 1 and all isNothing list == False both hold, so there must be at least a Just True in (map . fmap) p list.
But how do I pull out one single Bool out of that list?
I thought that I could take advantage of folding (e.g. via foldl) and Maybe's MonadPlus instance, doing something like the following:
ANSWER
Answered 2021-Sep-14 at 07:31This seems to work:
QUESTION
I was playing with cats' Monoids in scala when I see that the monoid operations are extended for Tuples in a natural way:
...ANSWER
Answered 2021-Oct-01 at 10:24Your question boils down to how implicit derivation of typeclasses for generic types work; so let's see two examples:
A case where we want to provide an instance no matter what the generic is:
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Install monoid
You can use monoid like any standard Python library. You will need to make sure that you have a development environment consisting of a Python distribution including header files, a compiler, pip, and git installed. Make sure that your pip, setuptools, and wheel are up to date. When using pip it is generally recommended to install packages in a virtual environment to avoid changes to the system.
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