You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
21 lines
592 B
Racket
21 lines
592 B
Racket
#lang racket/base
|
|
(require racket/contract racket/set)
|
|
|
|
(provide len)
|
|
|
|
(define/contract (has-length? x)
|
|
(any/c . -> . boolean?)
|
|
(ormap (λ(proc) (proc x)) (list list? string? symbol? vector? hash? set?)))
|
|
|
|
;; general way of asking for length
|
|
(define/contract (len x)
|
|
(any/c . -> . (or/c integer? #f))
|
|
(cond
|
|
[(list? x) (length x)]
|
|
[(string? x) (string-length x)]
|
|
[(symbol? x) (len (symbol->string x))]
|
|
[(vector? x) (len (vector->list x))]
|
|
[(hash? x) (len (hash-keys x))]
|
|
[(set? x) (len (set->list x))]
|
|
[(integer? x) (len (number->string x))]
|
|
[else #f])) |