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[ 0 => '{{infobox proglang', 1 => '|name=Reverse Polish Scheme', 2 => '|paradigms=Imperative, Stack-Based, Functional', 3 => '|author=[[User:McGoron|Peter McGoron]]', 4 => '|year=2025', 5 => '|class=Turing Complete', 6 => '|majorimpl=[https://github.com/mcgoron-peter/reverse-polish-scheme R4RS]', 7 => '|influence=Scheme, FORTH', 8 => '}}', 9 => '', 10 => ''''Reverse Polish Scheme''' (RPS) is a homoiconic, stack-based programming language with reified continuations. Its syntax is a subset of Scheme.', 11 => 'RPS can only use <code>call/cc</code> to manipulate the stack and instruction pointer. Stack operations, returns from calls, closures, delimited continuations, and all sorts of other fun things can be created using RPS's <code>call/cc</code>.', 12 => '', 13 => '== Core ==', 14 => '', 15 => 'RPS syntax is a subset of Scheme.', 16 => '', 17 => 'Line comments start with <code>;</code>. Nested block comments start with <code>#|</code> and end with <code>|#</code>. Writing a number, string, <code>#t</code>, or <code>#f</code> will push that literal value onto the stack. Writing an identifier will execute that identifier.', 18 => '', 19 => 'A literal vector is introduced with <code>#(</code> and ends with <code>)</code>. A literal list (a linked list where each list cell is a vector of two elements) starts with ( and ends with ). The empty list (nil) is represented by (). A literal identifier is introduced with <code>'</code>. (Note that lists and vectors are not quoted.)', 20 => '', 21 => 'A procedure is a linked list whose first element can be used for data storage, and whose tail is a linked list of instructions to execute. By convention, procedures that do not have any data to save in their first element have their first element be <code>#f</code>.', 22 => '', 23 => 'If the interpreter hits the end of a procedure, it will halt.', 24 => '', 25 => 'The following are the built in instructions. Instructions will execute and continue at the next instruction (exceptions are <code>call/cc</code> and <code>jump</code>). They will consume all specified arguments to them.', 26 => '', 27 => '{| class="wikitable"', 28 => '!Command', 29 => '!Description', 30 => '|-', 31 => '| style="text-align:center"| <code>proc to from call/cc</code>', 32 => '|The fundamental stack manipulator. Jump to <code>proc</code> with the continuation <code>cc</code> pushed to the stack. When <code>m cc jump</code> is called, control returns to the instruction after <code>call/cc</code>, except that the stack is the <code>m</code> values on the stack before the jump appended to the values on the stack from <code>from</code> inclusive to <code>to</code> exclusive at the site of call/cc's invocation. If <code>from</code> is <code>#f</code>, then it will capture the entire stack starting from <code>to</code> exclusive.', 33 => '|-', 34 => '| style="text-align:center"| <code>bool on-false on-true if</code>', 35 => '|If <code>bool</code> is <code>#f</code>, jump to the procedure <code>on-false</code>. Otherwise jump to the procedure <code>on-true</code>.', 36 => '|-', 37 => '| style="text-align:center"| <code>proc jump</code>', 38 => '|The next executed instruction will be the first instruction of <code>proc</code>. Note that is no return stack.', 39 => '|-', 40 => '| style="text-align:center"| <code>n vector</code>', 41 => '|Allocate a vector of <code>n</code> cells and push it to the stack.', 42 => '|-', 43 => '| style="text-align:center"| <code>vec vector-length</code>', 44 => '|Push the length in cells of <code>vec</code>. Returns <code>#f</code> if <code>vec</code> is not a vector.', 45 => '|-', 46 => '| style="text-align:center"| <code>vec n ref</code>', 47 => '|Push the <code>n</code>th cell of <code>vec</code> to the stack.', 48 => '|-', 49 => '| style="text-align:center"| <code>value n vec set!</code>', 50 => '|Set the <code>n</code>th cell of <code>vec</code> to <code>value</code>.', 51 => '|-', 52 => '| style="text-align:center"| <code>x y eqv?</code>', 53 => '|Pushes a boolean indicating if <code>x</code> and <code>y</code> are equivalent objects (i.e. the same vector or equal numbers).', 54 => '|-', 55 => '| style="text-align:center"| <code>x symbol?</code>', 56 => '|Pushes a boolean indicating if <code>x</code> is a symbol.', 57 => '|-', 58 => '| style="text-align:center" | <code>x integer?</code>', 59 => '|Pushes a boolean indicating if <code>x</code> is an exact integer.', 60 => '|-', 61 => '| style="text-align:center" | <code>x real?</code>', 62 => '|Pushes a boolean indicating if <code>x</code> is a real.', 63 => '|-', 64 => '| style="text-align:center" | <code>x y +</code>', 65 => '| Pushes <code>x + y</code>.', 66 => '|-', 67 => '| style="text-align:center" | <code>x y *</code>', 68 => '| Pushes <code>x * y</code>.', 69 => '|}', 70 => '', 71 => '== Examples ==', 72 => '', 73 => 'The stack is notated as if it was a LISP list. The first element of the list is the top of the stack.', 74 => '', 75 => 'The following code will duplicate the top of the stack.', 76 => '', 77 => ' 1 (#f jump) #f 1 call/cc', 78 => '', 79 => 'Explanation:', 80 => '', 81 => '* 1, a procedure, <code>#f</code>, 1 are pushed to the stack. The stack looks like <code>(1 #f &lt;proc&gt; 1 x values ...)</code>.', 82 => '* <code>call/cc</code> is invoked. It will jump to <code>&lt;proc&gt;</code> with the stack <code>(&lt;cc&gt; 1 x values ...)</code>.', 83 => '* <code>&lt;cc&gt;</code> is jumped into with the argument <code>1</code>. It will return to the position after the invocation of <code>call/cc</code>, pushing <code>x</code> onto a stack that was the stack at the invocation of <code>call/cc</code>, sans one element (the first 1 pushed). Hence the stack is <code>(x x values ...)</code>.', 84 => '', 85 => 'This code is normally inlined and used as a macro. A Lisp interpreter can be used as a value-level macro processor for RPS. Since there is no lexical scope, there is no need for hygienic macros. Quasiquote works well to splice in code.', 86 => '', 87 => '[[Category:Languages]]', 88 => '[[Category:Functional paradigm]]', 89 => '[[Category:2025]]', 90 => '[[Category:Stack-based]]', 91 => '[[Category:Turing complete]]', 92 => '[[Category:No IO]]', 93 => '[[Category:Implemented]]' ]