I think that doing your computations that require random numbers inside a monad that abstracts away the generator is the cleanest thing. Here is what that code would look like: We are going to put the StdGen instance in a state monad, then provide some sugar over the state monad’s get and set method to … Read more
some and many can be defined as: some f = (:) <$> f <*> many f many f = some f <|> pure [] Perhaps it helps to see how some would be written with monadic do syntax: some f = do x <- f xs <- many f return (x:xs) So some f runs … Read more
SET is the ANSI standard way of assigning values to variables, and SELECT is not. But you can use SELECT to assign values to more than one variable at a time. SET allows you to assign data to only one variable at a time. So that in performance is where SELECT will be a winner. … Read more
SET is the ANSI standard way of assigning values to variables, and SELECT is not. But you can use SELECT to assign values to more than one variable at a time. SET allows you to assign data to only one variable at a time. So that in performance is where SELECT will be a winner. … Read more
There is no reliable way to detect if a class is immutable. This is because there are so many ways a property of a class might be altered and you can’t detect all of them via reflection. The only way to get close to this is: Only allow final properties of types that are immutable … Read more
Tying the knot is a solution to the problem of circular data structures. In imperative languages you construct a circular structure by first creating a non-circular structure, and then going back and fixing up the pointers to add the circularity. Say you wanted a two-element circular list with the elements “0” and “1”. It would … Read more
I believe this is because the type for [] is inferred to be never[], which is the type for an array that MUST be empty. You can use a type cast to address this: [‘a’, ‘b’, ‘c’].reduce((accumulator, value) => accumulator.concat(value), [] as string[]); Normally this wouldn’t be much of a problem since TypeScript does a … Read more
Consider this: in all decent programming languages you can write functions, e.g. def f(arg) = result Here, f takes a value arg and computes a value result. It is a function from values to values. Now, some languages allow you to define polymorphic (aka generic) values: def empty<T> = new List<T>() Here, empty takes a … Read more
Pipes are a new feature in Pandas 0.16.2. Example: import pandas as pd from sklearn.datasets import load_iris x = load_iris() x = pd.DataFrame(x.data, columns=x.feature_names) def remove_units(df): df.columns = pd.Index(map(lambda x: x.replace(” (cm)”, “”), df.columns)) return df def length_times_width(df): df[‘sepal length*width’] = df[‘sepal length’] * df[‘sepal width’] df[‘petal length*width’] = df[‘petal length’] * df[‘petal width’] x.pipe(remove_units).pipe(length_times_width) … 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