#lang scheme

(require htdp/error)

;                                                   
;                                                   
;                                                   
;    ;;;                         ;;;                
;   ;   ;                       ;   ;               
;   ;                           ;   ;               
;   ;      ;   ;  ;;;;          ;   ;  ;   ;  ;   ; 
;    ;;;   ;   ;  ;   ;         ;;;;;  ;   ;   ; ;  
;       ;  ;   ;  ;   ;         ;   ;  ;   ;    ;   
;       ;  ;   ;  ;   ;         ;   ;  ;   ;    ;   
;   ;   ;  ;   ;  ;   ;         ;   ;  ;  ;;   ; ;  
;    ;;;    ;;;;  ;   ;         ;   ;   ;; ;  ;   ; 
;              ;                                    
;          ;   ;                                    
;           ;;;                                     

(provide nat> nat? proc> bool> num> ip> string> symbol>)

;; Any -> Boolean
(define (nat? x)
  (and (number? x) (integer? x) (>= x 0)))

;; Symbol X -> X
(define (bool> tag x)
  (check-arg tag (boolean? x) "boolean" "first" x)
  x)

;; Symbol X -> X
(define (string> tag x)
  (check-arg tag (string? x) "string" "first" x)
  x)

(define ip> string>)

;; Symbol X -> X
(define (symbol> tag x)
  (check-arg tag (symbol? x) "symbol" "second" x)
  x)

;; Symbol X Nat -> X
(define (proc> tag f ar)
  (check-proc tag f ar "first" 
              (if (> ar 1)
                  (format "~a arguments" ar)
                  "one argument"))
  f)

;; Symbol X (Number -> Boolean) String String -> X
(define (num> tag x pred? spec which)
  (check-arg tag (and (number? x) (pred? x)) spec which x)
  x)

;; Symbol X String -> X
(define (nat> tag x spec)
  (check-arg tag (nat? x) spec "natural number" x)
  x)