# Prosper

Prosper is a Forth-like stack-based language. While taking specific influence from Forth, it does not attempt to emulate or implement the ANS Forth standards.

Currently, the language is entirely interactive -- to explore, simply run `go run .` in the root of this project and an interactive session will begin.

## Syntax

Prosper is stack-based, as mentioned, so all the standard stack semantics are present:

```
> 1 2 3 4 + * -
ok
> .
-13 ok
```

New words can be defined using `: ;`:

```
> : SQUARE DUP * ;
ok
> 10 SQUARE .
100 ok
```

It has a single loop construct, `DO LOOP`:

```
> : TOFIVE 5 0 DO I . LOOP ;
ok
> TOFIVE
0 1 2 3 4 ok
```

Branches using `IF ELSE THEN` work:

```
> : EMOJI 0 < IF 128201 EMIT ELSE 128200 EMIT THEN ;
ok
> 100 EMOJI 
📈 ok
> -100 EMOJI
📉 ok
```

Here's a Fibonacci implementation:
```
> : FIB 2DUP + ;
ok
> : FIBN 0 1 ROT 1 DO FIB ROT DROP LOOP SWAP DROP ;
ok
> 10 FIBN .
55 ok
```

Propser also has a basic off-stack memory model using variables and pointers:
```
> VARIABLE FOO
ok
> 10 FOO !
ok
> FOO @
ok
> .
10 ok
```

And, of course, it knows how to quit:

```
> BYE
bye
```

## Future Plans

* Implement `CONSTANT`
* Implement loading libraries of pre-written functions both from the command-line and at run-time
* Add much better readline behaviors in the interactive console (up-arrow for history, cursor movement...)