kandi X-RAY | ReaderT Summary
kandi X-RAY | ReaderT Summary
Based on the modification of FBReaderJ, it imitates the epub reader with AppUI effect. (In development...)
Top functions reviewed by kandi - BETA
- Do the actual work .
- Synchronize the bookmarks .
- Process a text line .
- Updates the positions according to the float positions .
- Internal method used to draw this image .
- Loads books .
- Process text .
- Start downloading a file .
- Initializes the service .
- Parses an ATOMDateConstruct .
ReaderT Key Features
ReaderT Examples and Code Snippets
Trending Discussions on ReaderT
I found that
Reader is implemented based on
Identity. Why don't make
Reader first and then make
ReaderT? Is there specific reason to implement that way?
ANSWERAnswered 2022-Jan-11 at 17:11
They are the same data type to share as much code as possible between
ReaderT. As it stands, only
withReader have any special cases. And
withReader doesn't have any unique code, it's just a type specialization, so only two functions actually do anything special for
Reader as opposed to
You might look at the module exports and think that isn't buying much, but it actually is. There are a lot of instances defined for
Reader automatically has as well, because it's the same type. So it's actually a fair bit less code to have only one underlying type for the two.
Given that, your question boils down to asking why
Reader is implemented on top of
ReaderT, and not the other way around. And for that, well, it's just the only way that works.
Let's try to go the other direction and see what goes wrong.
I have a typeclass with a default implementation, and would like to provide a simple way to derive the typeclass if a user wants to use their custom monad.
Here's a solution someone else provided me:...
ANSWERAnswered 2022-Jan-01 at 21:35
As the error message says, your associated type
FooCtx depends only on
ctx, but not on
m, thus creating a potential for ambiguity like this:
Is there a way to avoid calling the "run" method twice and doing it just once from the main method or this is the right way to do it in nested Readers?...
ANSWERAnswered 2021-Dec-25 at 10:20
I'm not sure why you choose to define your services this way but if your question is to avoid calling
sumAndShow you could lift your
liftF and compose them with a
I have a function type declaration...
ANSWERAnswered 2021-Dec-10 at 21:59
I think this achieves what you want:
I'm trying to understand the purpose of Servant's serveWithContext function. The documentation states that it's not a replacement for the ReaderT Monad, but I'm uncertain as to what problem it's trying to solve that isn't already addressed by ReaderT.
For example, this is from the example on the servant-auth GitHub page:...
ANSWERAnswered 2021-Nov-22 at 22:16
It seems like the machinery of
Servant doesn't make assumptions about the underlying monad in which you choose to define the handlers. This means it can't force you to choose any particular monad (like, say,
ReaderT) in response to some combinator present in the routes, and it doesn't "react" to your choice of monad in order to enable some behavior.
Context system does it to collect that extra information in a positional parameter for
serveWithContext, while still letting you choose whatever monad you wish. The exact type of the parameter depends on what route combinators are present in the API.
The servant tutorial has some paragraphs about
When someone makes a request to our "private" API, we’re going to need to provide to servant the logic for validating usernames and passwords. [...] Servant 0.5 introduced Context to handle this. [...] the idea is simple: provide some data to the serve function, and that data is propagated to the functions that handle each combinator.
Furthermore, serveWithContext appears to be passing these values in twice
I'm not sure, but I suspect
jwts as parameters is done only as an example of how authentication would be performed if done purely in handlers, without help from Servant itself. In contrast, the
protected endpoint already receives the result of the authentication as a parameter; it doesn't have to perform it itself.
In a real-world application,
server wouldn't take those parameters, they would only be passed in the
I've written a simple Servant application that stores some information in an SQLite db file. Also, I created a generic function that runs a DB query:...
ANSWERAnswered 2021-Nov-03 at 20:24
I believe your problem is caused by a lack of understanding of monads. There are plenty of tutorials on the web, so allow me to simplify the issue and explain it in the context of your code.
When in Haskell we write
x :: Int, we mean that
x is an integer value. In the definition of
x we can write
I don't understand why this happens:...
ANSWERAnswered 2021-Oct-08 at 15:29
GHC 8.10.3 does complain about this with -Wall (after I changed
readConfig in your code):
A do-notation statement discarded a result of type ‘IO ()’
Suppress this warning by saying ‘_ <- print <$> readConfig c’
readConfig c of type
IO Int. Then you fmap
IO (IO ()). Since the result isn't bound to a variable in the do block, it is thrown away.
In the fmap's type
Functor f => (a -> b) -> f a -> f b we have
IO (). So it is used with the type
(Int -> IO ()) -> IO Int -> IO (IO ()).
This would work:
ANSWERAnswered 2021-Jul-01 at 09:13
At the time of writing this answer there is no way to have extension methods visible to trait constraints, although there is a longstanding RFC and PR in the F# compiler to implement it.
So, for the time being in order to add a type to an abstraction (like Monad) you need to either edit the type's source to add the required method or the abstraction source.
The former is basically impossible for
IObservable I mean you can try submit them a PR, but the latter option is more feasible in the short term: submit a PR or at least open an issue in F#+ to add
IObservable directly as Monad.
It might seem that this question is a duplicate of this question, however either Parsec or the Indent library has changed since 2012 and none of the old examples I have found for the indent library compile with the latest versions.
I want to make a parser for a programming language where indentation is part of the syntax (used to indicate scopes), in order to achieve this I want to make use of the Text.Parsec.Indent library, but I am at a loss on how to use it. It is clear to me that some modifications/custom parser type has to be made, but my limited knowledge on the State monad and surface level understanding of parsec seem to not be enough.
Let's say you wanted to make a parser for a simple list of ints like below. How would one achieve this?...
ANSWERAnswered 2021-Jun-25 at 14:04
Okay after some deep diving into the source code and looking at the tests in the indents GitHub repository I managed to create a working example.
The following code can parse a simple indented list:
Hi and thanks for your time. I'm trying to create a website that features a button that increments a counter. I want the current counter to be persistent and if somebody goes to my page, the current counter should be displayed. A request should be send every time I click the button to increment the counter. The request does not contain any information about the counter value. The server - in my case a warp web server - should update the counter value in the database, read the value after the update and then send it to the frontend if successful, of an error message if not.
So far, only the updating works, since I did not manage to figure out how to get the data from the database to the frontend. Here is the code from my Repository module that should do the updating:...
ANSWERAnswered 2021-Jun-24 at 18:44
You can ignore all the monadic parts of
getBy's type signature. Provided you get your code to type check,
counterEntity has type
Maybe (Entity Counter), and that's all that's important here.
Nothing if the query fails (i.e., no record in the table for that counter). Otherwise, it's
Entity Counter containing the retrieved record:
No vulnerabilities reported
You can use ReaderT like any standard Java library. Please include the the jar files in your classpath. You can also use any IDE and you can run and debug the ReaderT component as you would do with any other Java program. Best practice is to use a build tool that supports dependency management such as Maven or Gradle. For Maven installation, please refer maven.apache.org. For Gradle installation, please refer gradle.org .
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