Forth Interpreter

In this assignment, you will write an interpreter for a subset of the Forth programming language. A good tutorial can be found here, although your interpreter will not support all of the features discussed in the tutorial.

Here is the lexical specification and grammar for the subset of Forth you are interpreting:

(define the-lexical-spec
  '((whitespace (whitespace) skip)
    (comment ("\\" (arbno (not #\newline))) skip)
    (comment ("(" (arbno (not #\))) ")") skip)
    (number (digit (arbno digit)) number)
    (identifier
      ((or letter "." "!" "@" "$" "%" "^" "&" "*" "+" "-" "=" "/" "?" "<" ">")
       (arbno (or letter digit "." "!" "@" "$" "%" "^" "&" "*" "+" "-" "=" "/" "?" "<" ">")))
      symbol)))

(define the-grammar
  '((program ((arbno statement) "\n") a-program)
    (statement (number) num)
    (statement (identifier) word)
    (statement ("begin" (arbno statement) "while" (arbno statement) "repeat") loop-stmt)
    (statement ("if" (arbno statement) "else" (arbno statement) "then") if-stmt)
    (statement (":" identifier (arbno statement) ";") def)
    (statement ("+") add-prim)
    (statement ("-") sub-prim)
    (statement ("*") mult-prim)
    (statement ("/") div-prim)
    (statement (".") print-prim)
    (statement (">") gt-prim)
    (statement (">=") gte-prim)
    (statement ("cr") cr-prim)
    (statement ("drop") drop-prim)
    (statement ("dup") dup-prim)
    (statement ("over") over-prim)
    (statement ("swap") swap-prim)
    ))

--> 2 3 +
ok
--> .
5 ok
--> 2 3 4 + * .
14 ok
--> 1 if 2 else 3 then .
2 ok
--> : square dup * ;
(square) ok
--> 4 square .
16 ok
--> 10 1 begin over over >= while dup . 1 + repeat
1 2 3 4 5 6 7 8 9 10 ok
--> : fact dup 2 > if dup 1 - fact * else then ;
(fact square) ok
--> 5 fact .
120 ok

• Whenever a new word is defined, your interpreter prints a list of the defined words.
• Your interpreter does not require any special keyword for a recursive word. (This kind of interpreter is easier to write in Scheme.)