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Implementation suggestions:
The stages of evaluation are as follows:
Tokenization:: input a string and output a list of strings and numbers; for example, The 17-character string "(= (+ 3 55) 21)" should yield the following list of eight strings: (list "(" "=" "(" "+" 3 55 ")" 21 ")"). This can be done using a finite state machine with side effects; but you can do it any way you like.
Parsing: Input a list of strings and numbers, and output a nested list reflecting its original structure. For example, the input (list "(" "=" "(" "+" 3 55 ")" 21) should yield the output (list "=" (list "+" 3 5) 21). This can be done using a push down automaton; but you can do it any way you like.
Evaluate: Input a nested list of strings and numbers and output a number or true or false. For example, the input (list "=" (list "+" 3 5) 21)should yield an output of false. This can be done using recursion (there is no other reasonable way).
This means in Racket your eval function should look like this:
(def (eval s) (evaluate (parse (tokenize s))))
Email your commented source code as a single file to discrete.homework@gmail.com by midnight on May 15.
Grading will be as follows:
correct tokenizer: 25%
correct parser: 25%
correct evaluator: 25%
clear, concise documentation: 25%
Your documentation should include instructions on how to compile and test your program. If your project is incomplete, include in your documentation a description of which parts work and how to test them.
and this a pseudo code given for tokenizer
1 Input string
2 Variables: state = 'empty', chars = [], tokens = [], nextSate, nextChar (last two have no initial value)
3 while string is not empty:
Set nextChar equal to the first character of string
Set nextState equal to trans(state, nextChar) (trans is a helper function you must write)
If pushChar(state, nextState) then
push nextChar onto the back of chars. (pushCar is a Boolean helper function you must write)
If pushToken(state, nextState) then
push maketoken(chars) onto the back of tokens (maketoken is a helper function you must write. It converts strings to either strings or numbers).
set chars to the empty list
remove the first character from string
set state equal to nextState
4 return tokens
#lang racket
(define read-input(string))
(define state "empty")
(define chars '())
(define tokens '())
(define nextChar " " )
(define nextState " ")
(define (trans state nextChar)
(cond
[(equal? state " ")
(cond
[(equal? nextChar #\i) "i-if"]
[(equal? nextChar #\+) "addition"]
[(equal? nextChar #\*) "multiplication"]
[(equal? nextChar #\=) "equals"]
[(char-numeric? nextChar) "num"]
[else "error"])]
[(equal? state "number") (if (char-numeric? nextChar) "number" " ")]
[(equal? state "i-if") (if (equal? nextChar #\f) "f-if" "error")]
[else "error"]
))
;(define (pushChar state nextState)
;)/>
;(define (maketoken chars)
;)/>
;(define (pushToken state nextState)
;)/>
I am having trouble implementing
the functions above that have been commented out, can someone tell how to make sense of the pseudocode for part 3 4 and 5.
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