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# Reverse Polish Scheme
Reverse Polish Scheme (RPS) is a programming language for people who
think continuations are too easy to understand.
RPS is stack-based programming language vaguely based off of FORTH but
really just Scheme in disguise. RPS only has jumps: in order to return
from a procedure, you need to use `call/cc` to capture the current
continuation and pass it to the procedure.
## Core
Writing a number, a string, `#t`, `#f`, or `#nil` will push that literal
value onto the stack. Strings are equivalent to Scheme symbols. `#nil`
is the name of a value, NOT the symbol `"nil"`!
A linked list is a 2-vector whose second pair is either `#nil` or
another linked list.
A procedure is a linked list whose first slot is unused and whose code
starts in the second slot.
* `n alloc`: Allocate a memory region of `n` pointers.
* `{ ... }`: Reads all data up to the matching `{` as data. The data
is stored as a linked list.
* `v n ref`: Get the nth element of `v`.
* `value n v set!`: Set the nth element of `v`.
* `sr jump`: Jump to a procedure.
* `conditional on-false on-true if`: If `conditional` is truthy, jump
to `on-true`. Otherwise jump to `on-false`.
* `proc keep-bot keep-top call/cc`: Jump to `proc` with the continuation
pushed to the stack. The continuation object saves the last `keep-top`
objects on the stack along with the bottom `keep-bot` values on the
stack. If either is `#f`, then the entire stack is saved.
When `m cc jump` is called (where `cc` is the object returned by
`call/cc`), the `m` values currently on the stack are pushed to the top
of `n` values saved by `cc`, and control returns to the next location
after `call/cc`.
* `dir? n dig`: When `dir?` is false, move the `n`th value relative to the
top of the stack to the top of the stack. When `dir?` is true, move the
`n`th value relative to the bottom of the stack to the top of the stack.
* `dir? n bury`: When `dir?` is false, move the top value on the stack to
the `n`th value relative to the top of the stack. When `dir?` is true,
move the top of the stack to `n`th value relative to the bottom of
the stack.
* `dup`: Duplicate the top of the stack. This is a shallow copy.
* `drop`: Drop the top of the stack.
* `x y eqv?`: Compare two values on the top of the stack, returns a boolean.
## License
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
Version 2, December 2004
Copyright (C) 2025 Peter McGoron <code@mcgoron.com>
Everyone is permitted to copy and distribute verbatim or modified
copies of this license document, and changing it is allowed as long
as the name is changed.
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. You just DO WHAT THE FUCK YOU WANT TO.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
If you are concerned about the legalities of this license, then this
software is not for you. Go back to Java.
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