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Questions tagged [thunk]

A parameterless closure (functional programming) or a function generated by a compiler to aid runtime linking with a dynamic library function.

  • In functional programming, a thunk is an anonymous and parameterless function (closure), used to pass lazily evaluated expressions.
  • In C++, a thunk is a compiler generated function which optimizes virtual function calls.
  • On systems which support dynamic linking, a thunk is often automatically inserted to provide a place for the runtime linker to insert code for invoking the actual implementation found in a library.
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Scala lazy val caching

In the following example: def maybeTwice2(b: Boolean, i: => Int) = { lazy val j = i if (b) j+j else 0 } Why is hi not printed twice when I call it like: maybeTwice2(true, { println("hi"); 1+41 }) This example is actually from the book…
joesan
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Have Haskell expand certain thunks at compile time?

Is there a way to have Haskell expand certain thunks at run time. For example, say I have --Purposely inefficient code for demonstration fib 0=0 fib 1=1 fib n=fib n=fib (n-1) + fib (n-2) goldRatio=fib 100 / fib 101 How could I have it evaluate…
PyRulez
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More succinct delayed evaluation than function(){return x}?

I'm porting some Python code that relies heavily on delayed evaluation. This is accomplished by via thunks. More specifically, any Python expression for which delayed evaluation is desired gets enclosed within a Python "lambda expression",…
kjo
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Making Scala choose less specific overloaded method in presence of argument of type Nothing

If come across an interesting case with thunks versus functions in the presence of type Nothing: object Test { def apply(thunk: => Any ): String => Any = _ => thunk def apply(fun: String => Any): String => Any = fun } val res0 = Test {…
0__
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Using v-table thunks to chain procedure calls

I was reading some articles on net regarding Vtable thunks and I read somewhere that thunks can be used to hook /chain procedures calls. Is it achievable? Does anyone know how that works , also I am not able to find good resource explaining…
anand
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The value of ESP was not properly saved.... and C/C++ calling conventions

I am writing an application using the OpenCV libraries, the Boost libraries and a pieve of code that I have downloaded from this LINK. I have created a project under the same solution with Thunk32 and I have the following…
Nicolas Epaminonda
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Is the ATL incompatibility with DEP fixable?

ATL uses thunks to manage callbacks for windows, and apparently it needs to allow for data execution. Microsoft says: Note that system DEP policy can override, and having DEP AlwaysOn will disable ATL thunk emulation, regardless of the…
user541686
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Can we implement c++ thunk in linux?

I want to use class member functions as callbacks, I don't use libsigc, because it's slow. In ATL, we can use member function for C-style callback(http://www.codeproject.com/KB/cpp/SoloGenericCallBack.aspx), so can we implement c++ thunk in…
xufan
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Uncaught TypeError: Cannot read properties of undefined (reading 'then')?

saveProfile() does not return promise, although the person who has exactly the same code, the same function returns promise return async (dispatch, getState) => { const authUserId = getState().auth.id let data = await…
SeeYou1ater
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Can a getter return a thunk or value depending on the type call call (virt. property or function)?

I know this a weird question, but I'll ask it anyway. The pseudo code function below provides a virtual property getter. What it should do is this: > const calc = Calculator(3) > calc.multiple // returns getter result directly 6 >…
LongHike
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Error: Expected the root reducer to be a function. Instead, received: 'undefined'

I keep running into this error! Error: Expected the root reducer to be a function. Instead, received: 'undefined' I've tried every answer I could find to no avail, here is all the pertinent stuff! Root Reducer const createRootReducer = (history) =>…
Manny Ledoux
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Problem with Jest and dispatch with async functions

I am working with React + Redux (with thunk) and I am using Jest for testing. I have the next code: export const startUploading = (file) => { return async(dispatch, getState) => { const {active:activeNote} = getState().notes; …
queen_store
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useEffect() cause re-renders and multiple requests to api

Problem Functional component causes multiple re-renders causing multiple ajax requests. What is the solution for this? This is my code. export default function MyMenu() { let menu = useStoreState(state => state.menu.menu); const getMenu =…
Farman Ali
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Are thunk and function currying the same?

When I learn thunk, I think they are like function currying. Why is it called thunk? Thunk function add(x, y){ return x + y } function thunk() { return add(10, 20) } Function currying function multiply(a, b, c) { return a * b *…
Min Hein Khant
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Lazy evaluation, thunk and function closure in Scala

case class Test[A](elem: () => A) object Fun extends App { def test1(v: => Int): Test[Int] = Test(() => v) val a1 = test1({ println("hello"); 1 }) val a2 = a1.elem() //echoes hello val a3 = a1.elem() //echoes hello def test2(v: =>…
Rupam Bhattacharjee
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