StaDyn is an object-oriented general-purpose programming language for the .NET platform that supports both static and dynamic typing in the same programming language. The StaDyn compiler gathers type information for the dynamically typed code. That type information is used to detect type errors at compilation time and to perform significant optimizations. For that purpose, it provides type reconstruction (inference), flow-sensitive types, union and intersection types, constraint-based typing, alias analysis and method specialization.
Its first prototype appeared in 2007, as a modification of C# 3.0. Type inference was supported by including var as a new type, unlike C#, which only offers var to define initialized local variables. Flow-sensitive types of var references are inferred by the compiler, providing type safe duck typing [1]. When a more lenient approach is required by the programmer, the dynamic type could be used instead of var. Although type inference is still performed, dynamic references behave closer to those in dynamic languages.
Just download the latest release in a Windows computer with an installed .NET framework (default installations of Windows 10 and 11 already have one).
Create a hello.stadyn file:
using System;
public class HelloWorld {
public static void Main() {
var message;
message = "Hello world from StaDyn!";
Console.WriteLine(message);
}
}Compile it with:
StaDyn hello.stadyn
And run it:
hello.exe
We describe a summary of the main language features. For more information, please visit the StaDyn website or read our publications.
Just like dynamic languages, variables may hold different types in the same scope:
using System;
class Program {
public static void Main() {
Console.Write("Number: ");
var age = Console.In.ReadLine();
Console.WriteLine("Digits: " + age.Length);
age = Convert.ToInt32(age);
age++;
Console.WriteLine("Happy birthday, you are " + age +
" years old now.");
int length = age.Length; // * Compiler error
}
} The age variable is first inferred as string, so it is safe to get its Length property. Then, it holds an integer, so age++ is a valid expression. The compiler detects an error in the last line, since Length is no longer provided by age.
The generated code does not use a single Object variable to represent age, but two different variables whose types are string and int. This is achieved with a modification of the algorithm to compute the SSA form [2]. This makes the generated code to be more efficient, since runtime type conversions are not required.
var and dynamic variables can hold flow-sensitive types:
using System;
class Program {
public static void Main(String[] args) {
var exception;
if (args.Length > 0)
exception = new ApplicationException("An application exception.");
else
exception = new SystemException("A system exception.");
Console.WriteLine(exception.Message);
}
}It is safe to get the Message property from exception because both ApplicationException and SystemException provide that property. Otherwise, a compiler error is shown. In this way, StaDyn provides a type-safe static duck-typing system.
In the following program:
using System;
class Program {
public static void Main(String[] args) {
var exception;
switch (args.Length) {
case 0:
exception = new ApplicationException("An application exception.");
break;
case 1:
exception = new SystemException("A system exception.");
break;
default:
exception = "This is not an exception.";
break;
}
Console.WriteLine(exception.Message); // * Compiler error with var, but not with dynamic
Console.WriteLine(exception.Unknown); // * Compiler error
}
}The Message property is not provided by String, so a compiler error is shown for exception.Message. However, if we declare exception as dynamic, the previous program is accepted by the compiler. dynamic is more lenient than var, following the flavor of dynamic languages. However, static type checking is still performed. This is shown in the last line of code, where the compiler shows an error for exception.Unknown even if exception is declared as dynamic. This is because neither of the three possible types (ApplicationException, SystemException and String) supports the Unknown message [3].
Although dynamic and var types can be used explicitly to obtain safer or more lenient type checking, the dynamism of single var references can also be modified with command-line options, XML configuration files and a plugin for Visual Studio (see more details in [4]).
var and dynamic types can be used as object fields:
class Wrapper {
private var attribute;
public Wrapper(var attribute) {
this.attribute = attribute;
}
public var get() {
return attribute;
}
public void set(var attribute) {
this.attribute = attribute;
}
}
class Test {
public static void Main() {
string aString;
int aInt;
Wrapper wrapper = new Wrapper("Hello");
aString = wrapper.get();
aInt = wrapper.get(); // * Compiler error
wrapper.set(3);
aString = wrapper.get(); // * Compiler error
aInt = wrapper.get();
}
}The Wrapper class can wrap any type. Each time we call the set method, the type of attribute is inferred as the type of the argument. Each object has a potentially different type of attribute, so its type is stored for every single instance rather than for the whole class. In this way, the two lines indicated in the code above report compilation errors. A type-based alias analysis algorithm is implemented to support this behavior [5].
Let's analyze the following method:
public static var upper(var parameter) {
return parameter.ToUpper();
}The type of parameter and the function return value are inferred by the compiler. To that aim, a constraint is added to the type of the upper method: the argument must provide a ToUpper method with no parameters. At each invocation, the constraint will be checked. Additionally, the return type of upper will be inferred as the return type of the corresponding ToUpper method implemented by the argument [6].
The programmer may use either var or dynamic to declare parameter, changing the way type checking is performed upon method invocation. Let's assume that the argument passed to upper holds a flow-sensitive type (e.g., the ApplicationException, SystemException or String exception variable in the code above). With var, all the possible types of the argument must provide ToUpper; with dynamic, at least one type must provide ToUpper.
The type information gathered by StaDyn is used to perform significant optimizations in the generated code [7]: the number of type inspections and type casts are reduced, reflection is avoided, frequent types are cached, and methods with constraints are specialized. The point of all the optimizations is to reduce the number of type-checking operations performed at runtime, which is the main performance penalty of most dynamic languages. Many of those type checks are undertaken earlier by the StaDyn compiler.
A detailed evaluation of the runtime performance of StaDyn can be consulted in [1].
For more detailed information, please visit the StaDyn website.
[1] Francisco Ortin, Miguel Garcia, Sean McSweeney. Rule-based program specialization to optimize gradually typed code. Knowledge-Based Systems, volume 179, pp. 145-173. September 2019.
[2] Jose Quiroga, Francisco Ortin. SSA Transformations to Facilitate Type Inference in Dynamically Typed Code. The Computer Journal, volume 60, issue 90, pp. 1300-1315. September 2017.
[3] Francisco Ortin, Miguel Garcia. Union and intersection types to support both dynamic and static typing. Information Processing Letters, volume 111, issue 6, pp. 278-286. February 2011.
[4] Francisco Ortin, Francisco Moreno, Anton Morant. Static Type Information to Improve the IDE Features of Hybrid Dynamically and Statically Typed Languages. Journal of Visual Languages & Computing, volume 25, issue 4, pp. 346-362. August 2014.
[5] Francisco Ortin, Daniel Zapico, J. Baltasar García Perez-Schofield, Miguel Garcia. Including both Static and Dynamic Typing in the same Programming Language. IET Software, volume 4, issue 4, pp. 268-282. August 2010.
[6] Francisco Ortin. Type Inference to Optimize a Hybrid Statically and Dynamically Typed Language. The Computer Journal, volume 54, issue 11, pp. 1901-1924. November 2011.
[7] Miguel Garcia, Francisco Ortin, Jose Quiroga. Design and implementation of an efficient hybrid dynamic and static typing language. Software: Practice and Experience, volume 46, issue 2, pp. 199-226. February 2016.
Copyright 2006-2022 (C) Francisco Ortin. All rights reserved.