owainlewis / ava

Ava is a programming language exploring the idea of programs that can mutate and write themselves

AVA

Ava is a programming language exploring the idea of programs that can mutate and write themselves.

It is a stack based programming language, heavily inspired by Joy.

Ava programs are just a list of instructions. Ava supports the idea of quotations (meta programs) as a first class language construct.

Quotations are themselves Ava programs that can be evalulated. Unlike Joy, Ava quotations are distinct from lists.

Example

An Ava program is a sequence of instructions

Program = [ Instruction ]

A program may contain and generate other programs via quotations

Program A = [ { 1 2 3 } apply ] Program B = [ 1 2 3 ] ProgramA == ProgramB

Functions

Ava functions are just a list of instructions bound to an identifier

define square = [ dup * ]

Variables

Variables are immutable

let x = 10

let y = 20

Combinators

swap

a b swap => b a

i

The i combinator expects a quotation at the top of the stack.

{ P } i => P.

x

The x combinator

[P] x => [P] P

b

infra

L [M] [P] infra => L [N]

The infra combinator temporarily discards the current stack and takes M as the current stack state. It then executes the top quotation P which returns a new stack N. The new stack N is pushed back as a quotation onto the original stack

times

0 [P] times = id.
n [P] times = P (n-1) [P] times

branch

true  { P } { Q } branch => P.
false { P } { Q } branch => Q.

Instructions

The AVA language is made up of two layers. The lowest layer is a sequence of instructions that manipulate or modify a stack.

The lower level machine / VM instructions are

TPush
TPop
TDup
TSwap
TCons
TUncons
TChoice
TApply
TLet
TDefine
TStack
TUnstack
TInfra
TMult
TAdd
TSub
TDiv
TGt
TLt
TEq
TDot
TPrint
TNoop