Subterra

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Subterra is a tarpit-style language that attempts to get as close to being a proper imperative programming language as possible within the following restrictions:

  • Only single-character instructions
  • A single stack rather than variables
  • Integers are the only datatype (syntactic sugar excepted)

To this end, it implements a unique subroutine system that allows for simple pseudo-functions, as well as an import system (a rather unusual feature for a tarpit language).

Language reference

An up-to-date language reference is maintained on GitHub (see External Resources).

Computational class

Subterra is Turing-complete (and in fact has numerous Turing-complete subsets). The simplest way to show this is to see that the stack can be reversed using @, effectively making it into a double-ended queue (i.e. enough data storage ability for Turing-completeness), and the language has no shortage of useful control flow structures ({} subroutines don't do any stack manipulation, thus can be freely used for control flow without disturbing the data storage).

More complex Turing-completeness constructions also exist, e.g. using the call stack and the data stack as the two stacks required to store the required amount of data.

Examples

Hello, world!

Recursive:

0{s0>?{c0#}}"Hello world!"$0#

Non-recursive:

"Hello world!"w[0>]{bct1-}

99 bottles of beer

~ Includes proper plurals!

0 { w [0>] { bct1- } $ } ~ Simple print function

100 w {1-&0>} [
	&p" bottle"0#&1!?(\sc)" of beer on the wall,\n"0#
	&p" bottle"0#&1!?(\sc)" of beer,\n"0#
	"Take one down, pass it around,\n"0#
	1-&0=?("No"0#):[p]" bottle"0#&1!?(\sc)" of beer on the wall.\n\n"0#
]

Cat program

Recursive: (warning: will crash with large inputs!)

0{s0>?{c0#}}i$0#

Non-recursive:

iw[0>]{bct1-}

Collatz sequence

Change the 25 at the beginning to change the starting number.

25 w [1>] {
	&p10c
	&2%0!? {3*1+} : {2/}
} p

Factorial

Change the 5 on line 3 to change the input number.

0 { &1>?{&1-0#}s1>?{*} }

5;0#p

External resources