Picking Out Elements Using a Logical List

[roadrunner]

And another version using no declared variables and no for loop:

Code:

export BOOLLIST4(LA,LB)
BEGIN
 IF LB(1) THEN 
  IF size(LA)==1 THEN return LA(1);end;
  return concat(LA(1),BOOLLIST4(SUB(LA,2,size(LA)),CONCAT(SUB(LB,2,SIZE(LB)),LB(1)))​);
 end;
 if size(LA)==1 then return {};end;
 BOOLLIST4(SUB(LA,2,size(LA)),CONCAT(SUB(LB,2,SIZE(LB)),LB(1)));
END;