scheme

; Name: Christian Colglazier
; Date: 9-28-16

(define (eval-expr E env)
  (cond
    ; If E is a number than it stays a number
    ((number? E) E)

    ; Handles varibales
    ((symbol? E) (if (pair? (cadr (assoc E env)))
                     (set-car! (cdr (assoc E env))
                               (eval-expr (caadr (assoc E env)) (cadadr (assoc E env)))
                     )
                 )
                 (cadr (assoc E env))
    )

    ; Handles let
    ((eqv? (car E) 'let) (let* ((x  (caadr E))
                                (a (cadadr E))
                                (b (caddr E))
                                (r (eval-expr a env))
                                (newenv (cons (list x r) env))                               )
                         (eval-expr b newenv))
    )

    ; Handles call
    ((eqv? (car E) 'call) (eval-expr (caddr E) env) (display (cadr E)))
    
    ; Handles fucntions
    ((eqv? (car E) 'function) (lambda (cadr E) (caadr E)))
    
    ; Handles basic math operator
    ((eqv? (car E) 'plus) (apply + (eval-params (cdr E) env)))
    ((eqv? (car E) 'minus) (apply - (eval-params (cdr E) env)))
    ((eqv? (car E) 'times) (apply * (eval-params (cdr E) env)))
    ((eqv? (car E) 'divide) (apply / (eval-params (cdr E) env)))
    ; If operator
    ((eqv? (car E) 'if) (if (= (eval-expr (cadr E) env) 0) (eval-expr (cadddr E) env)(eval-expr (caddr E) env)))

    (else '())
  )
)

(define (eval-params E env)
  (if (null? E) '()
      (cons (eval-expr (car E) env) (eval-params (cdr E) env))
  )
)

; tests function and displays if it works or not.
(define (tester E env answer d)
  (cond
    ((eqv? d 0)(cond
      ((eq? (eval-expr E env) answer) (display "Works for ")
         (display E) (display " produced ") (display (eval-expr E env)) (newline))
      (else (display "!! Failed for ") (display E) (display " produced ") (display (eval-expr E env))(newline))                         
    ))
    (else (display (eval-expr E env)) (newline))
  )
)

; Sets the output mode of the test fucntion.
(define (test-mode) 0)

; Test fucntions based on examples from the assignment.
(define (test)
  (tester '(plus 3 5 4) '() 12 (test-mode))
  (tester '(times 3 5 4) '() 60 (test-mode))
  (tester '(minus 5 2 1) '() 2 (test-mode))
  (tester '(divide 10 5) '() 2 (test-mode))
  (tester '(divide 10 5 2) '() 1 (test-mode))
  (tester '(if (plus 1 2) (minus 3 5) (plus 5 6)) '() -2 (test-mode))
  (tester '(if (minus 2 2) (minus 3 5) (plus 5 6)) '() 11 (test-mode))
  (tester '(if (minus 2.0 2.0) (minus 3 5) (plus 5 6)) '() 11 (test-mode))
  (tester 'y '((y 20)) 20 (test-mode))
  (tester '(let (y (plus 1 4)) (times y y)) '() 25 (test-mode))
  (tester '(function d (plus d 1)) '() 4 (test-mode))
  (tester '(call (function z (plus z z)) (plus 5 3)) '() 16 (test-mode))
  ;Examples given from the assignment
  (tester '(plus 2 3) '( ) 5 (test-mode))
  (tester '(plus (times 2 3) (minus 4 2)) '( ) 8 (test-mode))
  (tester '(if (times 2 4) (plus 1 8) (divide 5 0)) '( ) 9 (test-mode))
  (tester '(if (minus 5 5) (divide 1 0) (plus 1 8)) '( ) 9 (test-mode))
  (tester 'x '((y 2) (x 5)) 5 (test-mode))
  (tester '(times x 3) '((x 5) (y 2)) 15 (test-mode))
  (tester '(times x 3) '((x 5) (x 2)) 15 (test-mode))
  (tester '(let (z 15) (plus z z)) '( ) 30 (test-mode))
  (tester '(let (r (plus 2 5)) (times r 2)) '( ) 14 (test-mode))
  (tester '(let (s 5) (let (t (plus s s)) (times s (plus t 3)))) '( ) 65 (test-mode))
  (tester '(let (f (function z (times z (plus w 1))))(call f (times 2 a))) '((a 5) (w 20)) 210 (test-mode))
)
(test)