eevo is a lightweight yet expressive, high-level scripting language for data-driven functional programming. A general-purpose language in the Lisp family that is ideal for scripting, acting as an interactive shell, data/configuration files, or a scientific calculator. eevo’s portable, simple design makes it easy to embed and extend, enabling integration into existing projects and straightforward use of established libraries. Forget the boilerplate and needless ceremony: focus on the what, and let eevo handle the how.

Everything should be as simple as possible, but not simpler

• Simple: Built on a minimal set of composable concepts. You can learn the entire language in an afternoon.
• Small: Extremely lightweight with less than 100KB binary from 2k lines of C99.
• Symmetric: Unification of many ideas with uniform syntax. Same principals and syntax are applied universally.
• Sweet: Syntactic sugar for easy and readable syntax, with invisible but powerful s-expressions underneath.
• Separable: Modular design allows you to use only what you need, or modify each component to suit your needs.
• Symbolic: Identifiers are first class citizens, allowing code to be manipulated like any data.
• Shareable: Bundled as a single universal executable makes it easy to run eevo code anywhere.

def fib(n)
  "Fibonacci number of n"
  if (< n 2)
    n
    + fib((- n 1)) fib((- n 2))

fib 25  ; = 46368

A lightweight modular core allows you to choose how much of the language you need. This comes in a few layers:

• Read/Print: Parse expressions and output data structures unevaluated (eg data or config files)
• Evaluate: Execute the code; transform and simplify expressions
• Core: Essential functions and syntax (eg flow control, list manipulation, basic math)
• Standard Library: Additional functions needed for common operations (eg IO, math, doc)
• Contrib: Community-driven libraries and scripts, officially sponsored (coming soon)

While eevo is a general purpose programming language, that does not mean it is the best tool for every problem. Like all languages, eevo has many design decisions which have trade-offs in different situations. To solve problems that are ill-suited to eevo’s design (such as requiring circular references or precise mutations) other languages can be called upon through C-bindings (and soon WASM).

This interoperability makes it easy to offload computationally heavy code to another language or gradually replace existing code with concise scripts. This enables a dual approach to bridge languages in two directions:

• Extend eevo by embedding another language as a library,
  • Out source computationally expensive code to low level libraries.
• Embed eevo to extend another program,
  • Slowly replace existing low level code with a high-level hackable scripting.

Both methods can be done at the same time with different languages, allowing eevo to glue different libraries, ecosystems, and tools together.

Features

High-level

• Developer can focus on important logic, not boiler-plate.
• Let eevo worry about implementation details, optimizations, data representation.

Functional programming

• All you need is data, and functions to transform that data.

Interactive

• Read, Evaluate, Print, Loop (REPL).

First Class Types

• Numbers: integers Int, decimals Dec, ratios Ratio.
• Booleans: True, Nil.
• Text: strings Str, symbols (identifiers/variables) Sym.
• Lists, pairs Pair,
• Code expressions.
• Records: Rec (hash tables/maps),
  • Look up tables, accept key and return corresponding value.
  • Unordered set of key value pairs.
  • Environments (namespaces/modules/capabilities).
• Functions: with closures Func,
  • Func for anonymous functions
  • Prim for external functions written in host language
• Macros:
  • Macro functions which transform code.
  • Form special forms which might not ovulate all their arguments. Written in host language.
• Types
• Void
• Errors

Functions as the universal type

• Records, arrays, dictionaries, environments, sets, types, strings are all modeled as functions.
• Functions are records with infinite many keys.
• Full unification still a work in progress.

Metaprogramming

• Homoiconic syntax allows for powerful and simple macro system.
• Abstract away boiler-plate, cost free.
• Customize syntax to extend language with new features.

Quoted expressions

• Code can be quoted to avoid (or delay) its evaluation.
• Allows code to be manipulated like data.
• Quasiquote enables some of the code to be unquoted and evaluated.

Literate Programming

• Write documentation directly inside an eevo script, which is converted to Markdown.

Tail call optimization

• Recursive loops become computationally equivalent to imperative loops.

Dyslexic friendly

• Primarily designed by someone with dyslexia. The language, standard library, and documentation are written to be as easy as possible to read.

See the language manual for complete set of features.

Anti-Features

Just like jazz, what is missing is often more insightful:

No mutations

• Mutations make programs difficult to predict and harder to read, increasing the mental load of every line of code.
  • Given the same code and data you always get the same result.
• Prevents the mistakes that come from half constructed values.
• Change should be modeled one way: function calls.
• Leave mutations as an optimization performed by the compiler.
• Allows for other easy optimizations such as automatic parallelization.
• Removes circular references, making automatic reference counting easy.

No dependencies (eg LLVM)

• Dependencies are just someone else’s code, which silently increase the surface error of potential bugs.
• Only relies on a C compiler and libc.

No statements

• Everything is an expression: 5, "hello", def, if, etc.

No keywords

• All symbols are equal and can be redefined at will.

No reader macros

• Limit amount of the language that can be modified.
• Should be easy to read anyone’s scripts.

No exceptions

• Errors are just regular values which have to be explicitly handled.

No multiple return values

• Just return a list, and require callee to explicitly expand into multiple values.

No explicit return

• Last item of procedure is always returned.
• Use Void to explicitly avoid returning last value.

No arrays, linked lists, or tuples

• Just pairs (2-tuples) and records.
• Lists and trees are constructed out of pairs.

No function currying

• Partial application should be explicit to avoid hard to debug accidents when you forget an argument.
• Functions only take one argument, but it is often a list of arguments.
• You are welcome to write functions in the curry style, but the standard library is not written that way.

No build systems

• Simply run the primary .evo file (by convention the same name as the project) and let it handle including and running all other files as needed.

No mandatory editor tools

• Syntax should be easy to modify without specialized tools.

No garbage collector

• Memory is managed through a simple bump allocator, with reference counting in the works.

Coming Soon…

Automatic reference counting memory management

• Memory is initially allocated on the stack with a region allocator.
• Values which escape their scope are evicted to the heap and reference counted.

Strong static typing with type inference

• First class.
• Algebraic data types (sum, product, exponential).
• Physical units,
  • Uncertainty.
• Polymorphism,
  • Row (record) polymorphism.
• Refinement types.
• Codata.
• Type holes.

Batteries included standard library

• While still being minimal and orthogonal.

Powerful string interpolation

• Doubles as a template processor (eg mustache).

First class algebraic pattern matching

• Function calls are already a form of pattern matching on lists,
  • Generalize this to any data pattern.

Improve error messages

Sandboxed

• Manage security and effects through capabilities via first class environments.

Full Unicode support

• Encoded in UTF-8.

Interoperability

• Support any programming language with C bindings.
• C, Lisp, Python, Lua, Rust, Go, etc.
• Remove requirement of C functions in specific form.

WebAssembly compiler

• Web interface, environment, and REPL.
• Javascript runtime.

Environmental image

• Restore the environment exactly how you left it.

Hygienic macros

• Avoid variable capture with macros.
• Simple without need for syntax-rules or gensym, similar to s7

Multithreading

Optimizations

• Total pre-computation
  • Anything that can be computed at compile time will be
  • Constant folding and propagation
• Opportunistic in place mutation
• Memorization (cache)
  • Strings and symbols are already interned
• Auto parallelism
  • GPU acceleration