You could use tails: gather n l = filter ((== n) . length) $ map (take n) $ tails l or using takeWhile instead of filter: gather n l = takeWhile ((== n) . length) $ map (take n) $ tails l EDIT: You can remove the filter step by dropping the last n elements … Read more
It’s pretty well-known that general function equality is undecidable in general, so you’ll have to pick a subset of the problem that you’re interested in. You might consider some of these partial solutions: Presburger arithmetic is a decidable fragment of first-order logic + arithmetic. The universe package offers function equality tests for total functions with … Read more
This library is a straightforward combinatorization of the well-known technique of memoization. Let’s start with the canonical example: fib = (map fib’ [0..] !!) where fib’ 0 = 0 fib’ 1 = 1 fib’ n = fib (n-1) + fib (n-2) I interpret what you said to mean that you know how and why this … Read more
Haskell is a lazy language. It doesn’t evaluate results until they are “needed”. Now, just printing a value causes all of it to be “needed”. In other words, if you type an expression in GHCi, it will try to print out the result, which causes it all to be evaluated. Usually that’s what you want. … Read more
The first issue can easily be bypassed by always providing a function with the right type a -> Promise a. Or by not using then as the bind operation of the monad, but some type-correct ones. Creed is a functionally minded promise library that provides map and chain methods which implements the Fantasy-land spec for … Read more
download glut from http://www.transmissionzero.co.uk/software/freeglut-devel/. Be sure to download the MinGW version. copy the file freeglut-MinGW-3.0.0-1.mp.zip\freeglut\bin\x64\freeglut.dll to C:\Windows\System32. Make sure you get the 64 bit version from the x64 folder. rename it as glut32.dll I just solved this problem and hope this could help others.
You can’t have an unsequence :: (Monad m) => m [a] -> [m a]. The problem lies with lists: you can’t be sure how may elements you are going to get with a list, and that complicates any reasonable definition of unsequence. Interestingly, if you were absolutely, 100% sure that the list inside the monad … Read more
One way to think of this is that a value of type IO a is a “recipe”, containing a list of instructions that if performed would have side effects. Constructing that “recipe” though, does not have any side effects. So a haskell program (whose type is IO ()) is basically a computation that constructs such … Read more
Using Data.Map and tuple sections: count = Map.fromListWith (+) . map (, 1) (Add Map.toList if you need a list.)
Let me use a shorter example than the posted one: original :: Int -> Int original n | n < 10 && n > 7 = 1 — matches 8,9 | n < 12 && n > 5 = 2 — matches 6,7,10,11 | n < 12 && n > 3 = 3 — matches … Read more