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
You can do this pretty straightforwardly with an implicit class and a for-comprehension in Scala 2.10: implicit class Crossable[X](xs: Traversable[X]) { def cross[Y](ys: Traversable[Y]) = for { x <- xs; y <- ys } yield (x, y) } val xs = Seq(1, 2) val ys = List(“hello”, “world”, “bye”) And now: scala> xs cross ys … Read more
In a pure functional language, you can’t do anything that has a side effect. A side effect would mean that evaluating an expression changes some internal state that would later cause evaluating the same expression to have a different result. In a pure functional language you can evaluate the same expression as often as you … Read more
Java 8 (released March 18th 2014) does support currying. The example Java code posted in the answer by missingfaktor can be rewritten as: import java.util.function.*; import static java.lang.System.out; // Tested with JDK 1.8.0-ea-b75 public class CurryingAndPartialFunctionApplication { public static void main(String[] args) { IntBinaryOperator simpleAdd = (a, b) -> a + b; IntFunction<IntUnaryOperator> curriedAdd = … Read more
rows.sortBy(r => (r.lastName, r.firstName))
The other uses I’ve found for it besides + and * were with and and or, but now we have any and all to replace those cases. foldl and foldr do come up in Scheme a lot… Here’s some cute usages: Flatten a list Goal: turn [[1, 2, 3], [4, 5], [6, 7, 8]] into … 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
In the 2009-2012 period, the following things have happened: 2012: From 2012, the parallel Haskell status updates began appearing in the Parallel Haskell Digest. 2011: Parallel and Concurrent Programming in Haskell, a tutorial. version 1.1 released by Simon Marlow Haskell and parallelism, mentioned in an article in the Economist magazine, Jun 2nd 2011. Parallel tree … Read more