 Forth is an imperative stack @-@ based computer programming language and environment originally designed by Charles " Chuck " Moore . Language features include structured programming , reflection ( the ability to modify the program structure during program execution ) , concatenative programming ( functions are composed with juxtaposition ) and extensibility ( the programmer can create new commands ) . Although not an acronym , the language 's name is sometimes spelled with all capital letters as FORTH , following the customary usage during its earlier years . 
