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BLooP

Language type:

S - block-structured

Description:

BLooP was a very simple recursive block structured language invented by Douglas Hofstadter for his book Godel, Escher, Bach. It features simple subroutine structure, very simple number and boolean handling, and recursion. The interesting aspect of BLooP was that it offered only bounded loop constructs, and was therefore incapable of expressing certain general recursive computations.

Origin:

Hofstader, 1979 (implementation: Cowan, 1994)

See Also:

FLooP   

Remarks:

Though Hofstadter doesn't mention it in GEB, BLooP is similar to early exercises in exploring the computational model of "Random Access Machines". Note the use of 'CELL(0) <= 2' and similar constructs.
Though BLooP was never intended to be more than an academic exercise, an implementation of BLooP in Perl was made. Unfortunately, I can't seem to find it.
It is interesting to note that, in order to limit the power of this language to only primitive recursive functions, and also not-so-coincidentally to make the halting problem for BLooP solvable, Dr. Hofstadter had to severly restrict the feature set of BLooP: no GOTOs, no While loops, etc.

Links:

http://www.geocities.com/ResearchTriangle/6100/geb.html

Implementation download

Date:

Last updated 12/6/00

Sample code:

From GEB, Chapter 13:

DEFINE PROCEDURE "GOLDBACH?" [N]:
BLOCK 0: BEGIN
        CELL(0) <= 2;
        LOOP AT MOST N TIMES:
        BLOCK 1: BEGIN
        IF {PRIME?[CELL(0)]
            AND PRIM[MINUS[N,CELL(0)]]},
        THEN:
           BLOCK 2: BEGIN
                OUTPUT <= YES;
                QUIT BLOCK 0;
           BLOCK 2: END
           CELL(0) <= CELL(0) + 1;
     BLOCK 1: END
BLOCK 0: END

Descriptions in this dictionary are ©1997-99 Neal Ziring. Some examples copyright of their respective authors. Some technologies and languages are trademarked. Permission to copy descriptions is granted as long as authorship credit is preserved.

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