As @ljedrz points out, to make it work you only need to reference the composed functions again: let finally = compose(&*multiply_and_add, &*divide_and_subtract); (Note that in Rust, convention dictates that variable names should be in snake_case) However, we can make this better! Since Rust 1.26, we can use abstract return types (previously featured gated as #![feature(conservative_impl_trait)]). … Read more
The word “functor” comes from category theory, which is a very general, very abstract branch of mathematics. It has been borrowed by designers of functional languages in at least two different ways. In the ML family of languages, a functor is a module that takes one or more other modules as a parameter. It’s considered … Read more
Just look at the Wikipedia article to get your definition: Tacit programming (point-free programming) is a programming paradigm in which a function definition does not include information regarding its arguments, using combinators and function composition […] instead of variables. Haskell example: Conventional (you specify the arguments explicitly): sum (x:xs) = x + (sum xs) sum … Read more
I think @Vijay’s answer is the best one so far and I just intend to Erlangify it. Pairs (cons cells) in Erlang are written as [Head|Tail] and nil is written as []. There is no restriction as to what the head and tail are but if you use the tail to chain more cons cells … Read more
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