You can have nested iterations in a single list comprehension: [filename for path in dirs for filename in os.listdir(path)] which is equivalent (at least functionally) to: filenames = [] for path in dirs: for filename in os.listdir(path): filenames.append(filename)
Silver Spoon Evaluation We’ll just start with tracing the evaluation of addSquare(3, 1) // … Ok, here goes = flow([add, trace(‘after add’), square]) (3, 1) add(3,1) 4 trace(‘after add’) (4) tap(x => console.log(`== ${ ‘after add’ }: ${ x }`)) (4) curry((interceptor, n) => { interceptor(n); return n; }) (x => console.log(`== ${ ‘after add’ … Read more
Hindley-Milner is a type system discovered independently by Roger Hindley (who was looking at logic) and later by Robin Milner (who was looking at programming languages). The advantages of Hindley-Milner are It supports polymorphic functions; for example, a function that can give you the length of the list independent of the type of the elements, … Read more
One key feature in a functional language is the concept of first-class functions. The idea is that you can pass functions as parameters to other functions and return them as values. Functional programming involves writing code that does not change state. The primary reason for doing so is so that successive calls to a function … Read more
No, that’s not a closure. Your example is simply a function that returns the result of incrementing a static variable. Here’s how a closure would work: function makeCounter( int x ) { return int counter() { return x++; } } c = makeCounter( 3 ); printf( “%d” c() ); => 4 printf( “%d” c() ); … Read more
Objects are poor man’s closures. Consider Java. Java is an object-oriented programming language with no language level support for real lexical closures. As a work-around Java programmers use anonymous inner classes that can close over the variables available in lexical scope (provided they’re final). In this sense, objects are poor man’s closures. Closures are poor … Read more
Understanding pattern matching requires explaining three parts: Algebraic data types. What pattern matching is Why its awesome. Algebraic data types in a nutshell ML-like functional languages allow you define simple data types called “disjoint unions” or “algebraic data types”. These data structures are simple containers, and can be recursively defined. For example: type ‘a list … Read more
A functional language (ideally) allows you to write a mathematical function, i.e. a function that takes n arguments and returns a value. If the program is executed, this function is logically evaluated as needed.1 A procedural language, on the other hand, performs a series of sequential steps. (There’s a way of transforming sequential logic into … Read more
Or if you play a video game, there are tons of state variables, beginning with the positions of all the characters, who tend to move around constantly. How can you possibly do anything useful without keeping track of changing values? If you’re interested, here’s a series of articles which describe game programming with Erlang. You … Read more
Read Functional Programming in a Nutshell. There are lots of advantages to stateless programming, not least of which is dramatically multithreaded and concurrent code. To put it bluntly, mutable state is enemy of multithreaded code. If values are immutable by default, programmers don’t need to worry about one thread mutating the value of shared state … Read more