#lang racket/base
(require (for-syntax racket/base))

(provide (all-defined-out))

(define max-char-num #x10FFFF)

(struct lex-abbrev (get-abbrev))
(struct lex-trans (f))

(module+ test 
  (require rackunit))

(define-syntax (test-block stx)
  (syntax-case stx ()
    [(_ defs (code right-ans) ...)
     #'(module+ test
         (require rackunit)
         (let* defs
           (let ([real-ans code])
             (check-equal? real-ans right-ans)) ...))]))

#;(define-syntax test-block
    (syntax-rules ()
      ((_ x ...) (void))))


;; A cache is (X ( -> Y) -> Y)
;; make-cache : -> cache
;; table map Xs to Ys.  If key is mapped, its value is returned.
;; Otherwise, build is invoked and its result is placed in the table and
;; returned.
;; Xs are compared with equal?
(define (make-cache)
  (let ([table (make-hash)])
    (λ (key build)
      (hash-ref table key (λ ()
                            (let ([new (build)])
                              (hash-set! table key new)
                              new))))))

(module+ test
  (define cache (make-cache))
  (check-equal? (cache '(s 1 2) (λ () 9)) 9)
  (check-equal? (cache '(s 2 1) (λ () 8)) 8)
  (check-equal? (cache '(s 1 2) (λ () 1)) 9)
  (check-equal? (cache (cons 's (cons 0 (cons +inf.0 10)))
                       (λ () 22)) 22)
  (check-equal? (cache (cons 's (cons 0 (cons +inf.0 10)))
                       (λ () 1)) 22))



;; make-counter : -> -> nat
;; makes a function that returns a higher number by 1, each time
;; it is called.
(define (make-counter)
  (let ([counter 0])
    (λ ()
      (begin0
        counter
        (set! counter (add1 counter))))))

(module+ test 
  (define c (make-counter))
  (define d (make-counter))
  (check-equal? (c) 0)
  (check-equal? (d) 0)
  (check-equal? (c) 1)
  (check-equal? (d) 1)
  (check-equal? (c) 2))


;; remove-dups : (list-of X) (X -> number) -> (list-of X)
;; removes the entries from l that have the same index as a
;; previous entry.  l must be grouped by indexes.
(define (remove-dups l index acc)
  (cond
    [(null? l) (reverse acc)]
    [(null? acc) (remove-dups (cdr l) index (cons (car l) acc))]
    [(= (index (car acc)) (index (car l)))
     (remove-dups (cdr l) index acc)]
    [else 
     (remove-dups (cdr l) index (cons (car l) acc))]))


(module+ test
  (check-equal? (remove-dups '((1 2) (2 2) (1 3) (1 4)
                                     (100 4) (0 5)) cadr null)
                '((1 2) (1 3) (1 4) (0 5)))
  (check-equal? (remove-dups null error null) null))

;; do-simple-equiv : (list-of X) (X -> nat) -> (list-of X)
;; Sorts l according to index and removes the entries with duplicate
;; indexes.
(define (do-simple-equiv l index)
  (define ordered (sort l (λ (a b) (< (index a) (index b)))))
  (remove-dups ordered index null))

(module+ test
  (check-equal? (do-simple-equiv '((2 2) (1 4) (1 2)
                                         (100 4) (1 3)  (0 5)) 
                                 cadr)
                '((2 2) (1 3) (1 4) (0 5)))
  (check-equal? (do-simple-equiv null error) null))

;; replace : (list-of X) (X -> bool) (X -> (list-of X)) (list-of X) ->
;;           (list-of X)
;; If (pred? r) for some r in l, splice (get r) in place of r in the resulting
;; list.
(define (replace l pred? get acc)
  (cond
    [(null? l) acc]
    [(pred? (car l)) (replace (cdr l) pred? get (append (get (car l)) acc))]
    [else (replace (cdr l) pred? get (cons (car l) acc))]))       


(module+ test
  (check-equal? (replace null void (λ () (list 1)) null) null)
  (check-equal? (replace '(1 2 3 4 3 5)
                         (λ (x) (= x 3))
                         (λ (x) (list 1 2 3))
                         null)
                '(5 1 2 3 4 1 2 3 2 1)))