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sugar/len.rkt

21 lines
634 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 (error "len: cant calculate length of" x)]))