kandi X-RAY | dry-transaction Summary
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Trending Discussions on Functional Programming
I have been trying to learn about functional programming, but I still struggle with thinking like a functional programmer. One such hangup is how one would implement index-heavy operations which rely strongly on loops/order-of-execution.
For example, consider the following Java code:...
ANSWERAnswered 2022-Mar-07 at 21:17
This is not an index-heavy operation, in fact you can do this with a one-liner with
scanl1 :: (a -> a -> a) -> [a] -> [a]:
I want to write a function that checks if the first list is longer than the second list and one of them can be infinite. However I can't find a working solution....
ANSWERAnswered 2022-Mar-22 at 20:54
Plain old natural numbers will not do the trick, because you can't calculate the natural number length of an infinite list in finite time. However, lazy natural numbers can do it.
Haskell provides a convenient function
forever that repeats a monadic effect indefinitely. It can be defined as follows:
ANSWERAnswered 2022-Feb-05 at 20:34
The execution engine starts off with a pointer to your loop, and lazily expands it as it needs to find out what
IO action to execute next. With your definition of
forever, here's what a few iterations of the loop like like in terms of "objects stored in memory":
I was solving a recursive problem in haskell, although I could get the solution I would like to cache outputs of sub problems since has over lapping sub-problem property.
The question is, given a grid of dimension
n*m, and an integer
k, how many ways are there to reach the gird (n, m) from (1, 1) with not more than k change of direction?
Here is the code without of memoization...
ANSWERAnswered 2021-Dec-16 at 16:23
In Haskell these kinds of things aren't the most trivial ones, indeed. You would really like to have some in-place mutations going on to save up on memory and time, so I don't see any better way than equipping the frightening
This could be done over various data structures, arrays, vectors, repa tensors. I chose
HashTable from hashtables because it is the simplest to use and is performant enough to make sense in my example.
First of all, introduction:
I have a function in Haskell that is defined as follows:...
ANSWERAnswered 2021-Nov-30 at 09:42
Haskell values have types. Each value has a type. One type. It can't be two different types at the same time.
x is returned as the result of
if's consequent, the type of the whole
if ... then ... else ... expression is the same as
if expression has a type. Thus both its consequent and alternative expression must have that same type, since either of them can be returned, depending on the value of the test. Thus both must have the same type.
x is also used in the test, it must be
Bool. Then so must be
What is the syntax for a vector (array) of functions in APL?
I have tried the following but these are interpreted as a 3-train and a 2-train, respectively:...
ANSWERAnswered 2021-Nov-28 at 23:26
Dyalog APL does not officially support function arrays, you can awkwardly emulate them by creating an array of namespaces with identically named functions.
In F# if I write...
ANSWERAnswered 2021-Nov-17 at 01:24
To expand on the answer given in the comments, the first
p is an immutable value, while the second
p is a function. If you refer to an immutable value multiple times, then (obviously) its value doesn't change over time. But if you invoke a function multiple times, it executes each time, even if the arguments are the same each time.
Note that this is true even for pure functional languages, such as Haskell. If you want to avoid this execution cost, there's a specific technique called memoization that can be used to return cached results when the same inputs occur again. However, memoization has its own costs, and I'm not aware of any mainstream functional language that automatically memoizes all function calls.
I'm working trough the book Haskell in depth and I noticed following code example:...
ANSWERAnswered 2021-Nov-03 at 06:39
Reader's type parameters aren't in the right order for that to be
contramap for it. A
Contravariant functor always needs to be contravariant in its last type parameter, but
Reader is contravariant in its first type parameter. But you can do this:
I am experimenting with clojure's lazy sequences. In order to see when the evaluation of an item would occur, I created a function called square that prints the result before returning it. I then apply this function to a vector using map....
ANSWERAnswered 2021-Oct-20 at 15:49
Laziness isn't all-or-nothing, but some implementations of seq operate on 'chunks' of the input sequence (see here for an explanation). This is the case for vector which you can test for with
Haskell lists are constructed by a sequence of calls to
cons, after desugaring syntax:
ANSWERAnswered 2021-Aug-30 at 04:46
Lists in Haskell are special in syntax, but not fundamentally.
Fundamentally, Haskell list is defined like this:
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