# dumb-stack-lang

This is a tinkering repo for an interpreted stack-based language implemented in Haskell.
God help you if you want to use this for anything.

## Current features

### Datatypes

* Booleans
* Arbitrary-prescision integers
* Strings

### Procedures

Custom procedures can be created before the main body of the program:

```
PROC is-even? 2 OVER % 0 == END

4 is-even? . '''true'''
5 is-even? . '''false'''
PROC illegal "this is an error" . END ''' not allowed, defined after body program body '''
```

### Postfix/Reverse Polish notation

Procedures are invoked by pushing its arguments to the stack in reverse order and then calling the procedure:

```
''' compute 2+1 and print the result (3) '''
1 2 + .

''' compute 2-1 and print the result (1) '''
1 2 - .

''' compute 1-2 and print the result (-1) '''
2 1 - .

''' test if 5 is greater than 6 and print the result (false) '''
6 5 > .

''' compute 2+3, test if 3 is less than the sum, and print the result '''
3 2 + 3 < .

''' concatenate two strings and print the result '''
" but backwards" "it's like LISP" ++ .

```

### Comments

Comments are multi-line only and are opened and closed with three single-quotes:

```
IF 2 9 % 0 == DO
  ''' TODO: come up with a better message to print
  maybe something to do with the mod result being 0? '''
  "true branch"
ELSE
  ''' i feel like we could mention that the number is odd? or something? '''
  "false branch"
END .
```

### Control-flow

DSL currently has IF/ELIF/ELSE blocks and WHILE loops:

```
IF get-some-number 0 == DO
  "the number is zero" .
ELIF get-some-number 1 == DO
  "the number is one" .
ELIF get-some-number 2 == DO
  "the number is two" .
ELSE
  "this number has yet to be discovered by science" .
END
```

### Special characters

Most characters typically thought-of as 'special' have no special syntactic meaning in DSL. Some exceptions include:

* Double-quotes, which start and end string literals
* Three single-quotes in a row, which start and end comment blocks
* Other special character sequences already reserved as intrinsic / proc names

```
''' this is okay '''
PROC $(*^$%*&#$%# "this is a string that was just printed" . END

''' this isn't '''
PROC "foo "this is a parser error" . END
```