The age of type inference

Main stream languages have been continuously adopting good ideas from functional programming. Java and C# has gradually added programming constructs such as garbage collection, parametric polymorphism, lambda expressions and closures.

In spit of these ongoing endeavors, dynamically typed languages such as Python, Ruby, JavaScript and even Clojure are gaining popularity over statically typed languages. These languages are concise and elegant, and you don’t need to spend your precious time writing complex type annotations.

To regain the power stolen by dynamic languages, statically typed main stream languages have begun to introduce local type inference. For example, C++11 added auto keyword, which directs the compiler to use the initialization expression of a declared variable to deduce its type. Java and C# also added similar constructs.

#include <iostream>
using namespace std;
int main( )
    int count = 10;
    int& countRef = count;
    auto myAuto = countRef;
    countRef = 11;
    cout << count << " ";
    myAuto = 12;
    cout << count << endl;

Unfortunately, the power of type inference in these languages are very limited. Because type inference is tightly coupled with type system, we can’t introduce global type inference such as Hindler-Milner to these languages. Because of compatibility, it is practically impossible to retrofit the type system to allow global type inference.

I think it is time to design and implement a new statically typed language which looks almost the same to dynamic typed languages. Developers from Python, Ruby and JavaScript must be able to use it without learning how to put types all over the program. Dynamic vs Static typing controversy is meaningless if you don’t need to annotate any type in both languages. A statically typed language is always better because it detects errors at compile time for free.

Daniel Spiewak expects in his talk that statically typed languages with structural type systems (necessary for type inference) will dominate in the future and I totally agree with him.

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