(add-to-load-path ".")
(add-to-load-path "util/")
(add-to-load-path "prelude/")

(use-modules (environment))
(use-modules (prelude/primitives))
(use-modules (util/alist))

(define (tagged? expr tag)
  (if (pair? expr)
      (eq? (car expr) tag)
      #f))

;;; self-evaluating
(define (self-evaluating? expr)
  (or (number? expr)
      (string? expr)
      (bool? expr)))

(define variable? symbol?)

;;; if-else
(define (make-if predicate consequent alternative)
  (list 'if predicate consequent alternative))
(define (if-else? expr) (tagged? expr 'if))
(define (if-predicate expr) (cadr expr))
(define (if-consequent expr) (caddr expr))
(define (if-alternative expr) 
  (if (not (null? (cdddr expr)))
      (cadddr expr)
      'false))

;;; cond forms
(define (cond-form? expr) (tagged? expr 'cond))
(define (cond-clauses expr) (cdr expr))
(define (cond-predicate clause) (car clause))
(define (cond-consequent clause) (cadr clause))
(define (cond-else? clause) (tagged? clause 'else))
(define (last-clause? clauses) (null? (cdr clauses)))
(define (make-cond clauses) (cons 'cond clauses))
(define (cond->if expr)
  (let ([clauses (cond-clauses expr)])
    (cond
      [(cond-else? (car clauses)) (cond-consequent (car clauses))]
      [(last-clause? clauses) (make-if (cond-predicate (car clauses))
                                       (cond-consequent (car clauses))
                                       '())]
      [else (make-if (cond-predicate (car clauses))
                     (cond-consequent (car clauses))
                     (cond->if (make-cond (cdr clauses))))])))


;;; function application
(define (function-application? expr) (pair? expr))
(define (operator expr) (car expr))
(define (operands expr) (cdr expr))
(define (no-operands? expr) (null? expr))
(define (list-of-values ls env)
  (map (lambda (l) (eval-expr l env)) ls))

;;; quoted expressions
(define (quote-form? expr) (tagged? expr 'quote))
(define (quotation-text expr) (cadr expr))

;;; assignment
(define (assignment? expr) (tagged? expr 'set!))

(define (eval-expr expr env)
  (cond
    [(self-evaluating? expr) expr]
    [(if-else? expr) (eval-if expr env)]
    [(cond-form? expr) (eval-cond expr env)]
    [(quote-form? expr) (quotation-text expr)]
    [(function-application? expr)
     (apply-expr (operator expr)
                 (list-of-values (operands expr) env))]))

(define (eval-if expr env)
  (if (true? (eval-expr (if-predicate expr) env))
      (eval-expr (if-consequent expr) env)
      (eval-expr (if-alternative expr) env)))

(define (eval-cond expr env)
  (eval-expr (cond->if expr) env))

(define (primitive? proc)
  (is-elem-assoc-list proc primitives))

(define (apply-primitive-proc proc args)
  (let ([p (lookup-assoc-list proc primitives)])
    (apply p args)))

(define (apply-expr proc args)
  (cond
    [(primitive? proc) (apply-primitive-proc proc args)]
    [else 'false]))

(define the-global-env (setup-environment))
(define input-prompt ";;; CIRCLE INPUT ")
(define output-prompt ";;; CIRCLE OUTPUT ")
(define (driver-loop)
  (begin
    (newline)
    (display input-prompt)
    (newline)
  (let ([input (read)])
    (let ([output (eval-expr input the-global-env)])
      (begin
        (display output-prompt)
        (newline)
        (show-lisp-expr output)
        (newline)
        (driver-loop))))))

(define (show-lisp-expr object)
  (display object))