Zest is a (very wip) programming language for building systems that are both malleable and legible.

The goal is to:

• Support the interactivity and liveness of systems like emacs without giving up on civilized luxuries like static typing, early binding, jump-to-definition, load-order independence etc.
• Support the kinds of interactions I explored in research prototypes like eve and imp but from the well-trodden ground of a mostly-familiar imperative language.

A good place to start reading is docs/rationale.md. You can also find more notes at scattered-thoughts.net/#zest.

status

• Basic control flow, arithmetic, comparisons, functions etc work.
  • Break/continue/return are missing
  • Mutually recursive functions are not supported yet (the interaction with staging is tricky, see #1).
• There are 2nd-class mutable references, but dynamic/static prevention of aliasing is incomplete.
• The type system, specialization, and compile-time evaluation more or less work, but the ergonomics could be improved.
• Code can either be interpreted or compiled, but there is no support yet for mixing both within a single program.
• Interpreted code leaks memory. Compiled code stack-allocates everything (which is safe because type-system prevents references escaping). There is no heap allocation and no memory management yet. The allocator exists in /lib/runtime.zest but hooking it up to the language requires solving #1 first.
• The only error-handling available is panic.

docs and tests

The docs contain embedded tests that look like this:

// code
1 + 1

// result
2

When the lax and strict dialects produce different results, there will be two results in the test:

// code
1 + 'foo'

// lax result
Cannot call zest.Builtin.add with these args: { 1, 'foo' }

// strict result
Cannot call zest.Builtin.add with these args: { i64, string }

The strict dialect doesn't currently have a way to print values from inside the wasm sandbox, so any test that returns a non-integer value will only print undefined in the strict dialect.

'foo'

'foo'

undefined

The implementation is in flux. Generally, the docs text will describe the intended behaviour, but the tests will show the current behaviour. The tests can be automatically updated with zig run lib/test.zig -- --rewrite docs/*.md.