side-effects

This is not a duplicate of Assignment inside lambda expression in Python , i.e., I'm not asking how to trick Python into assigning in a lambda expression. I have some λ-calculus background. Considering the following code, it looks like Python is quite willing to perform side-effects in lambda expressions: #!/usr/bin/python def applyTo42(f): return f(42) def double(x): return x * 2 class ContainsVal: def __init__(self, v): self.v = v def store(self, v): self.v = v def main(): print('== functional, no side effects') print('-- print the double of 42') print(applyTo42(double)) print('-- print 1000

I am learning Scala right in these days. I have a slight familiarity with Haskell, although I cannot claim to know it well. Parenthetical remark for those who are not familiar with Haskell One trait that I like in Haskell is that not only functions are first-class citizens, but side effects (let me call them actions) are. An action that, when executed, will endow you with a value of type a , belongs to a specific type IO a . You can pass these actions around pretty much like any other value, and combine them in interesting ways. In fact, combining the side effects is the only way in Haskell to

I'm using the code below to free up memory on some running programs because my own program needs large memory resources to run faster. [DllImport("psapi.dll")] public static extern bool EmptyWorkingSet(IntPtr hProcess); public FreeMem(string programName){ EmptyWorkingSet(Process.GetCurrentProcess().Handle); foreach(Process process in Process.GetProcesses(programName)) { try { EmptyWorkingSet(process.Handle); } catch (Exception) { ... } } } It seems to be working fine, I was able to bring down memory usage of some programs like explorer from 100,000 Kb down to 2,000 Kb. That's pretty good but

I am trying to evolve my understanding of side effects and how they should be controlled and applied. In the following List of flights, I want to set a property of each flight satisfying a conditions: IEnumerable<FlightResults> fResults = getResultsFromProvider(); //Set all non-stop flights description fResults.Where(flight => flight.NonStop) .Select(flight => flight.Description = "Fly Direct!"); In this expression, I have a side effect on my list. From my limited knowledge I know for ex. "LINQ is used for queries only" and "There are only a few operations to lists and assigning or setting

This question already has an answer here: Why are these constructs using pre and post-increment undefined behavior? 14 answers Imagine that we have the code below: int i = 1; int j = i++ + ++i; I know that this is a Undefined Behavior, because before the semicolon, which is a sequence point, the value of i has been changed more than once. It means that the compiler may have two possibilities even if the precedence of operator plus is Left-to-Right: case 1) take the value of i++ --- value of i is 1 take the value of ++i --- value of i is 2 do the operator plus and assign the result which is 3

I'm feeling rather silly asking this question, but it's been on my mind for a while and I can't find any answers. So the question is: why can applicative functors have side effects, but functors can't? Maybe they can and I've just never noticed...? This answer is a bit of an over-simplification, but if we define side effects as computations being affected by previous computations, it's easy to see that the Functor typeclass is insufficient for side effects simply because there is no way to chain multiple computations. class Functor f where fmap :: (a -> b) -> f a -> f b The only thing a