6.1.1730
J
 
CORE
Interpretation:
Interpretation semantics for this word are undefined.

Execution:
( -- n | u ) ( R: loop-sys1 loop-sys2 -- loop-sys1 loop-sys2 )

n | u is a copy of the next-outer loop index. An ambiguous condition exists if the loop control parameters of the next-outer loop, loop-sys1, are unavailable.

See:
A.6.1.1730 J.

Rationale:
J may only be used with a nested DO ... LOOP, DO ... +LOOP, ?DO ... LOOP, or ?DO ... +LOOP, for example, in the form:

   : X ... DO ... DO ... J ... LOOP ... +LOOP ... ;

Testing:
T{ : GD3 DO 1 0 DO J LOOP LOOP ; -> }T
T{          4        1 GD3 ->  1 2 3   }T
T{          2       -1 GD3 -> -1 0 1   }T
T{ MID-UINT+1 MID-UINT GD3 -> MID-UINT }T

T{ : GD4 DO 1 0 DO J LOOP -1 +LOOP ; -> }T
T{        1          4 GD4 -> 4 3 2 1             }T
T{       -1          2 GD4 -> 2 1 0 -1            }T
T{ MID-UINT MID-UINT+1 GD4 -> MID-UINT+1 MID-UINT }T