PinnedType Inference by ExampleIf you’re implementing a programming language, you might be pondering how to do type inference. Instead of going through the theory, we’ll go through some examples to build an intuition for how it works, and finally see how to put that into code. Consider the following function: function f(x) {…Programming Languages2 min readProgramming Languages2 min read
PinnedAsync/await inference in FireflyFirefly is a new general purpose programming language that tries to achieve convenience and safety at the same time, by using pervasive dependency injection. There is no global access to the file system, the network, other processes or devices. Instead, you access these through a system object that is passed…Programming Languages2 min readProgramming Languages2 min read
Jul 9, 2021Row polymorphism crash courseWith type inference, structural records types can make a statically typed language feel almost like a scripting language, without giving up type safety: // Works for any record with the fields width, height : Float area2d v = v.width * v.height Row polymorphism can be used to implement this, and…2 min read2 min read
Apr 18, 2020Type Inference by Example, Part 7Continuing where we left off in part 6, let’s add in mutually recursive functions with generics. Consider the following example: function even(x) { return x == 0 || odd(x - 1); } function odd(x) { return x != 0 && even(x - 1); } We say that these functions are…Programming Languages5 min readProgramming Languages5 min read
Published inThe Startup·Apr 15, 2020Member-onlyType Inference by Example, Part 6Continuing where we left off in part 5, let’s extend the language and reconstruct the missing type annotations in the syntax tree. First, we’ll extend the lambda function syntax and application so that it supports multiple arguments. case class ELambda( parameters : List[Parameter], returnType : Option[Type], body…Programming Languages4 min readProgramming Languages4 min read
Apr 13, 2020Member-onlyType Inference by Example, Part 5Continuing where we left off in part 4, let’s finish implementing a first version of the type inference — and see a small demo. The first thing we’ll need is a language to infer types for. Let’s start with the lambda calculus: sealed abstract class Expression case class ELambda(x : String…Programming Languages3 min readProgramming Languages3 min read
Apr 12, 2020Type Inference by Example, Part 4Continuing where we left off in part 3, let’s take a look at unification. The first thing we’ll need is a representation for types. Let’s look at the types we’ve seen so far: Int — a plain type Array<Int> — a generic type (Int, Int) => Int — a function…Programming Languages4 min readProgramming Languages4 min read
Apr 11, 2020Type Inference by Example, Part 3Continuing where we left off in part 2, we’ll now consider calling a generic function: function map<A, B>(array : Array<A>, body : A => B) : Array<B> So this is the classic map function that applies a lambda function body to each element of the array and returns a new…Programming Languages2 min readProgramming Languages2 min read
Apr 10, 2020Type Inference by Example, Part 2Continuing where we left off in part 1, let’s look at a more advanced example that uses local variables and type constructors: function range(from, to) { let numbers = []; for(let i = from; i <= to; i++) { numbers[i - from] = i; } return numbers; } As in…Programming Languages3 min readProgramming Languages3 min read
