Ditch

Ditch is an esolang by User:BoundedBeans where syntax is irreversibly changed periodically.

Syntax

Ditch is a bit like Forth. It has a stack and words that operate on it, though you cannot define your own. However, in Ditch, all data is strings. Strings are enclosed in double quotes and only have two escape sequences: ?", for escaping quotes, and ??, for escaping question marks.

Levels

At level 0, the following operations can be performed in postfix:

+	concatenation of two strings
>	the first character
<	everything except the first character
	The following 5 commands definitions are the same as in Forth.
:	dup
/	swap
$	drop
%	rot
^	over
	End forth copying.
_	pop x and use its length as a zero-based index from the top of the stack, pick that element and copy it to the top.
=	pushes "a" if the top two strings are equal, "" otherwise
|	pushes the length of the string in unary "a"
begin ... until	as in forth, but the empty string is falsy and everything else is truthy
if ... else ... then	as in forth, but the empty string is falsy and everything else is truthy
.	outputs the top string
,	inputs a line

After 5 instructions excluding keywords and string literals, the program automatically and irreversibly "ditches" the code to the next level, resetting the counter back to zero. The stack is preserved when ditching.

At any level besides level 0, there is only one operation:

@

eval the top string as the previous level. It is an error if a ditch occurs inside of this, unless enclosed within a block. Note that the 5 instruction limit applies to every level, but separately. 5 instructions on level 1 can simulate 25 instructions at level 0. Eval uses the same stack as normal. Eval can have the string preloaded ahead of time, and when it's executing the contents, instructions can manipulate the stuff below.

Inside of a block, the level is separate. It is possible to have a block ditch and then recover once it exits the block (from any amount of levels). This is to allow conditionals and loops that are longer than a tiny amount of commands. Because of this, commands inside of blocks do not count towards the 5 outside the block, but they do inside. This would require a stack of levels to implement. It can just as well do this inside of eval, although it would need to get down to level zero in order to even use blocks.

Let's make a one line cat and see how it transforms.

Level 0:

, .

Level 1:

", ." @

Level 2:

"?", .?" @" @

Level 3:

"?"???", .???" @?" @" @

Level 4:

"?"???"???????", .???????" @???" @?" @" @

Examples

Hello world!

"Hello world!" .

Truth-machine

, : "0" = / / "if . else begin : . ?"?" until then" @