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FLooP

Language type:

S - block-structured

Description:

FLooP 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. Unlike its cousin BLooP, FLooP does support unbounded loops. This allows it to possess the full power of a Turing machine, thus making it fair game for various undecidability theorums. The syntax of FLooP is rather verbose, but simple in structure.

Origin:

Hofstader, 1979 (implementation: Cowan, 1994)

See Also:

BLooP   

Remarks:

Though Hofstadter doesn't mention it in GEB, FLooP 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 FLooP was never intended to be more than an academic exercise, an implementation of FLooP in Perl was made. Unfortunately, I can't seem to find it.

Links:

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

BLoop/FLoop Implementation Download

Date:

Last updated 12/6/00

Sample code:

DEFINE PROCEDURE ''DIVIDE'' [DIVIDEND, DIVISOR]:
  BLOCK 0: BEGIN
    IF DIVISOR < 1, THEN: QUIT BLOCK 0;
    CELL(0) <= DIVIDEND;
    LOOP AT MOST DIVIDEND TIMES:
      BLOCK 1: BEGIN
        IF CELL(0) < DIVISOR, THEN: QUIT BLOCK 0;
        CELL(0) <= MINUS[CELL(0), DIVISOR];
        OUTPUT <= OUTPUT + 1;
      BLOCK 1: END;
  BLOCK0: END.

DEFINE PROCEDURE ''PERFECT?'' [N]:
BLOCK 0: BEGIN
  CELL(0) <= 0;
  CELL(1) <= 0;
  LOOP DIVIDE [N,2] TIMES:
  BLOCK 1 BEGIN:
    CELL(1) <= CELL(1) + 1;
    IF REMAINDER[N,CELL(1)] = 0, THEN: CELL <= CELL(0) + CELL(1);
  BLOCK 1 END;
  IF CELL(0) = N THEN: OUTPUT <= YES;
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.

Comments on this dictionary, corrections and suggestions, are all welcome. Please use email, the address is ziring@home.com