6.1.2380
UNLOOP
 
CORE
Interpretation:
Interpretation semantics for this word are undefined.

Execution:
( -- ) ( R: loop-sys -- )

Discard the loop-control parameters for the current nesting level. An UNLOOP is required for each nesting level before the definition may be EXITed. An ambiguous condition exists if the loop-control parameters are unavailable.

See:
3.2.3.3 Return stack, A.6.1.2380 UNLOOP.

Rationale:
Typical use:
: X ...
   limit first DO
   ... test IF ... UNLOOP EXIT THEN ...
   LOOP ...
;

UNLOOP allows the use of EXIT within the context of DO ... LOOP and related do-loop constructs. UNLOOP as a function has been called UNDO. UNLOOP is more indicative of the action: nothing gets undone — we simply stop doing it.

Testing:
T{ : GD6 ( PAT: {0 0},{0 0}{1 0}{1 1},{0 0}{1 0}{1 1}{2 0}{2 1}{2 2} ) 
      0 SWAP 0 DO 
         I 1+ 0 DO 
           I J + 3 = IF I UNLOOP I UNLOOP EXIT THEN 1+ 
         LOOP 
      LOOP ; -> }T
T{ 1 GD6 -> 1 }T
T{ 2 GD6 -> 3 }T
T{ 3 GD6 -> 4 1 2 }T