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Stacks inside stacks inside stacks...
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RETURN (my favorite stack type in DUP) is a stack-based language inspired by DUP. It is an attempt to improve upon DUP in a way that allows more programming tasks to be solved more easily.


RETURN is different from other stack-based languages in that there are multiple stacks. You get 2 parent stacks, and new children stacks can be created along the way. There are different commands to switch between and manipulate stacks.

RETURN uses ISO-8859-1.


  • 0-9: Push number to stack. You may need to separate series of numbers with whitespace.
  • \0: Find all indices of top item in stack, or return -1 if not found.
  • \1: Switch parent stacks.
  • \2: Duplicate top n items into a new stack.
  • \3: Reverse stack.
  • \4: Transpose stack.
  • \5: Flatten stack.
  • \6: Sort stack.
  • \7: Get stack length.
  • \b: Concatenate top 2 items.
  • \t: Split the stack into chunks.
  • \n: Generate a range between top 2 numbers.
  • \v: Repeat stack by top item.
  • \f: Push to other parent stack.
  • \x0e: Get top item from other parent stack.
  • {: Set top item as current stack.
  • }: Get out of current stack into surrounding stack.
  • %: Drop top item.
  • $: Duplicate top item.
  • ¤: Pick 2nd item from top.
  • \: Swap top 2 items.
  • @: Pull nth item to top.
  • ª: Push item to nth index.
  • ø: Duplicate nth item from top.
  • +-×^: Add/subtract/multiply/pow top 2 items.
  • ÷: Divmod top 2 items (mod first, then div).
  • ¿: Push random binary number to stack.
  • Ð: Push milliseconds elapsed since January 1, 1970 00:00:00 UTC.
  • &|: Perform bitwise AND/XOR on top 2 items.
  • ~: Perform bitwise NOT on top item.
  • «»: Perform logical left/right shift on top 2 items.
  • ±: Get sign of top item.
  • <: Check if top item is less than 0.
  • >: Check if top item is greater than 0.
  • 'a: Push subsequent charcode to stack.
  • "...": Push a series of charcodes to a new stack until another " is met.
  • ¦: Split a number into a stack with its individual digits.
  • §: Join a stack into a number.
  • ¨: Split a stack along top item.
  • °: Join stack with top item.
  • .: Output top item.
  • ,: Output top item as charcode.
  • `: Push entire input into a new stack.
  • :: Store 2nd item from top to top item.
  • ;: Get stored value from top item.
  • ¥: Coerces null to 0, and anything else to -1.
  • [...]: Push lambda to stack.
  • !: Execute lambda.
  • [...][...]?: Executes 2nd lambda from top if 3rd item from top is truthy; otherwise, executes top lambda.
  • [...][...]#: Executes top lambda while condition (returned by 2nd lambda from top) is truthy.
  • [...]=a: Define top lambda as operator.


"Hello, world!":

"Hello, world!",





Infinite loop:


Factorial (requires input number to be on stack):

5 1+1␊␅[¤][×]#

Fibonacci Sequence (infinite loop):


Thue-Morse Sequence (infinite loop):

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