The eval Programming Language 1.0

eval (express(ive) versatile all-purpose language) is a modern general-purpose programming language with a focus on simplicity, safety and soundness. eval is compiled to JavaScript which makes it a natural choice for state of the art projects in the field of web technology.

• Statically Typed

  As opposed to many mainstream languages like Java, C#, C++, etc. for which soundness of the type system cannot be proven, eval has a verifiably sound and complete but yet flexible static type system, which is strictly more powerful than Hindley-Milner type systems and features:

  • Dependent types
  • Linear types
  • Intersection and Union types
  • Existential types
  • Gradual typing

• Object Oriented

  eval is a pure object oriented language, fulfilling all rules of object oriented languages as defined by Alan Kay.

• Functional

  eval is purely functional. Functions are first class citizens. eval features advanced functional concepts like

  • Strict and lazy evaluation
  • Ad-Hoc polymorphism through type classes
  • Automatic derivation of all type classes
  • Type signatures can include proof obligations which are checked by the compiler.

Try eval online!!

Optimized Language Core

What further differentiates eval from other mainstream languages, is that we are able to maintain on par expressitivity and computational universality while optimizing the language core to eliminate declarations as well as type signatures of all kinds.

Standard Library

The standard library defines four types

• () (Unit type)
• String,
• α -> ⁠β (Function type),
• IO α (Abstracts away side effects in the style of Haskell IO)

As well as three type classes ApplicativeFunctor, Monad, Monoid.

In addition there exists one object eval of type String -> IO (). The function evaluates the provided String as a javascript program.

Eval is bootstrapped!

The eval compiler is completely written in eval. Bootstrapping a compiler hase several advantages (Source: Wikipedia):

• it is a non-trivial test of the language being compiled, and as such is a form of dogfooding.
• compiler developers only need to know the language being compiled.
• compiler development can be done in the higher level language being compiled.
• improvements to the compiler's back-end improve not only general purpose programs but also the compiler itself.
• it is a comprehensive consistency check as it should be able to reproduce its own object code.

Thanks to the expressitivity of the eval programming language, the compiler consists of just 0.001 KLOC. See evalc.eval to get an idea of advanced programming in eval.

Hello World

Here comes the obligatory hello world example:

eval("alert('Hello World!')")

Syntax

eval syntax is actually quite simple and can be expressed by the following EBNF:

Program = Expression;
Expression = FunctionCall | Identifier | Literal;
FunctionCall = Expression, '(', Expression, ')';
Identifier = 'eval';
Literal = StringLiteral;
StringLiteral = '"', { StringCharacter }, '"';
StringCharacter = AnyCharacterExceptDoubleQuotes | '\', '"';

Whitespace is not allowed in eval outside of string literals.

Type-Checker

Thanks to the optimized language core it is possible to implement the type checking very efficiently in one phase together with the syntax analysis by allowing only correctly typed programs to be parsed.

A top level expression has to be of type IO (). There is only one expression which satisfies this type. Namely eval(x) where x is of type String. Only string literals are of type String which boils down to the following regular expression which does all the necessary name resolutions and type checks:

/eval\("([^"]|\\")*"\)/

License

eval is copyright 2016 by Martin Ring

MIT License