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Forth

Forth. Lecture L7.1. A Brief History of Programming Languages. http://www.byte.com/art/9509/sec7/art19.htm. http://merd.net/pixel/language-study/diagram.html. How would you have a computer evaluate this expression?. X = A*B + (C – D)/(E + F). Reverse Polish Notation (RPN) Postfix

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Forth

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  1. Forth Lecture L7.1

  2. A Brief History of Programming Languages http://www.byte.com/art/9509/sec7/art19.htm http://merd.net/pixel/language-study/diagram.html

  3. How would you have a computer evaluate this expression? X = A*B + (C – D)/(E + F) Reverse Polish Notation (RPN) Postfix AB*CD-EF+/+

  4. Forth http://www.ultratechnology.com/dindex.htm

  5. WHYP • Pronounced “whip” • “Words to Help You Program” • Subroutine-threaded Forth for Embedded Systems • 68HC11 (16-bit) • 68332 (32-bit) • 68HC12 (16-bit)

  6. WHYP is developed from scratch in the book:Design of Embedded Systems Using 68HC12/11 MicrocontrollersbyRichard E. HaskellPrentice Hall, 2000

  7. FORTH is a programming language that --- • was invented by Charles Moore in the early 70’s • is extensible • keeps all definitions in a dictionary • is extremely compact • is recursive • can be programmed in RAM, PROM, or ROM • is structured • uses a stack and postfix notation

  8. Chuck Moore reading Haskell’s WHYP book

  9. WHYP Colon Definitions : squared ( n -- n**2) DUP * ; : cubed ( n -- n**3) DUP \ n n squared \ n n**2 * ; \ n**3

  10. Branching and Looping in WHYP • IF…ELSE…THEN • FOR…NEXT • BEGIN…AGAIN • BEGIN…UNTIL • BEGIN…WHILE…REPEAT

  11. IF…ELSE…THEN <cond> IF <true statements> ELSE <false statements> THEN <cond> is either TRUE (-1) or FALSE (0)

  12. WHYP Conditional Words < ( n1 n2 -- f ) (“less-than”) > ( n1 n2 -- f ) (“greater-than”) = ( n1 n2 -- f ) (“equals”) <> ( n1 n2 -- f ) (“not-equals”) <= ( n1 n2 -- f ) (“less-than or equal”) >= ( n1 n2 -- f ) (“greater-than or equal”) 0< ( n -- f) (“zero-less”) 0> ( n -- f) (“zero-greater”) 0= ( n -- f) (“zero-equal”) U< ( u1 u2 -- f ) (“U-less-than”) U> ( u1 u2 -- f ) (“U-greater-than”) U<= ( u1 u2 -- f ) (“U-less-than or equal”) U>= ( u1 u2 -- f ) (“U-greater-than or equal”)

  13. Do different things depending what is in T : checkT ( n -- ) DUP 1 = \ n f IF \ n DO1 \ ELSE \ n DUP 2 = \ n f IF \ n DO2 ELSE \ n DUP 3 = \ n f IF \ n DO3 ELSE \ n DO4 THEN \ THEN THEN ;

  14. FOR…NEXT Loop n FOR <WHYP statements> NEXT >R drjne <WHYP statements> Decrement top of return stack and branch back to <WHYP statements> if not equal to zero. Therefore, <WHYP statements> are executed n times.

  15. BEGIN…AGAIN BEGIN <WHYP statements> AGAIN

  16. BEGIN…UNTIL BEGIN <WHYP statements> <flag> UNTIL <flag> is either TRUE or FALSE usually from some WHYP conditional word

  17. : GET.BTN ( -- n ) BEGIN BEGIN BTN@ 0= UNTIL BEGIN BTN@ UNTIL BTN@ CHECKT AGAIN ;

  18. BEGIN…WHILE…REPEAT BEGIN <words> <flag> WHILE <words> REPEAT

  19. Factorial x = 1 i = 2 DO WHILE i <= n x = x * i i = i + 1 ENDDO factorial = x : factorial ( n -- n! ) 1 2 ROT \ x i n BEGIN \ x i n 2DUP <= \ x i n f WHILE \ x i n -ROT TUCK \ n i x i * SWAP \ n x i 1+ ROT \ x i n REPEAT \ x i n 2DROP ; \ x

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