 In most Forth systems , the body of a code definition consists of either machine language , or some form of threaded code . The original Forth which follows the informal FIG standard ( Forth Interest Group ) , is a <unk> ( <unk> Interpretive Language ) . This is also called indirect @-@ threaded code , but direct @-@ threaded and subroutine threaded Forths have also become popular in modern times . The fastest modern Forths use subroutine threading , insert simple words as macros , and perform peephole optimization or other optimizing strategies to make the code smaller and faster . 
