Editing BlooP and FlooP (section)

==BlooP examples==

The only [[variable (programming)|variable]]s are <code>OUTPUT</code> (the return value of the procedure) and <code>CELL(''i'')</code> (an unbounded sequence of natural-number variables, indexed by constants, as in the [[Counter machine models#1963: Shepherdson and Sturgis' model|Unlimited Register Machine]]<ref>Hofstadter refers to these cells as a set of "auxiliary variables."</ref>). The only [[operator (programming)|operator]]s are <code>⇐</code> ([[assignment (computer science)|assignment]]), <code>+</code> (addition), <code>×</code> (multiplication), <code>&lt;</code> (less-than), <code>&gt;</code> (greater-than) and <code>=</code> (equals).

Each program uses only a finite number of cells, but the numbers in the cells can be arbitrarily large. Data structures such as lists or stacks can be handled by interpreting the number in a cell in specific ways, that is, by [[Gödel numbering for sequences|Gödel numbering]] the possible structures.

Control flow constructs include bounded loops, [[Conditional (programming)|conditional statements]], <code>ABORT</code> jumps out of loops, and <code>QUIT</code> jumps out of blocks. BlooP does not permit recursion, unrestricted jumps, or anything else that would have the same effect as the unbounded loops of FlooP. Named procedures can be defined, but these can call only previously defined procedures.<ref>Hofstadter (1979), p. 413.</ref>

=== Factorial function ===
{{pre|
DEFINE PROCEDURE ''FACTORIAL'' [N]:
BLOCK 0: BEGIN
        OUTPUT ⇐ 1;
        CELL(0) ⇐ 1;
        LOOP AT MOST N TIMES:
        BLOCK 1: BEGIN
                OUTPUT ⇐ OUTPUT × CELL(0);
                CELL(0) ⇐ CELL(0) + 1;
        BLOCK 1: END;
BLOCK 0: END.
}}

=== Subtraction function ===
This is not a built-in operation and (being defined on natural numbers) never gives a negative result (e.g. 2 &minus; 3 := 0). Note that <code>OUTPUT</code> starts at 0, like all the <code>CELL</code>s, and therefore requires no initialization.

{{pre|1=
DEFINE PROCEDURE ''MINUS'' [M,N]:
BLOCK 0: BEGIN
        IF M < N, THEN:
        QUIT BLOCK 0;
        LOOP AT MOST M + 1 TIMES:
        BLOCK 1: BEGIN
                IF OUTPUT + N = M, THEN:
                ABORT LOOP 1;
                OUTPUT ⇐ OUTPUT + 1;
        BLOCK 1: END;
BLOCK 0: END.
}}