<HTML><BODY>> Why does list? allow a vector in the following contract? Contract in `provide' is used only when you `require' your module from other. If you want always test it, use define/contract > Also, how do I indicate an optional (in this case keyword) argument? <a href="http://docs.racket-lang.org/reference/function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%2A%29%29">http://docs.racket-lang.org/reference/function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%2A%29%29</a> (->* (list? exact-nonnegative-integer?) (#:splice boolean?) any) Tue, 19 Aug 2014 22:44:57 -0700 от Kevin Forchione <lysseus@gmail.com>: <blockquote style="border-left:1px solid #0857A6; margin:10px; padding:0 0 0 10px;"> <div id=""> <div class="js-helper js-readmsg-msg"> <style type="text/css"></style> <div> <base target="_self" href="https://e.mail.ru/"> <div id="style_14085143380000000112_BODY">Hi guys, In an attempt to tighten up my code I started using the raise-xxxx-error feature and then began looking at contracts. I like the concept and think it would lead to cleaner looking code But I have two questions: Why does list? allow a vector in the following contract? Also, how do I indicate an optional (in this case keyword) argument? (I’m assuming I’d have to define a contract to handle the valid exact-nonnegative-integer/range for the index, unless there is one already defined. I’ll have a go at that later. ) #lang racket (provide (contract-out (insert-at (list? exact-nonnegative-integer? any/c . -> . any)))) (define (insert-at lst index val #:splice (splice #f)) #;(unless (list? lst) (raise-argument-error 'insert-at "list?" lst)) #;(uqnless (exact-nonnegative-integer? index) (raise-argument-error 'insert-at "exact-nonnegative-integer?" index)) #;(unless (<= index (length lst)) (raise-range-error 'insert-at "list" "" index lst 0 (length lst))) #;(unless (boolean? splice) (raise-argument-error 'insert-at "boolean?" splice)) (define-values (head tail) (split-at lst index)) (append head (cond [(and splice (cons? val)) val] [else (list val)]) tail)) >(insert-at #(a b) 0 ‘c) '(c . #(a b)) Thanks! -Kevin ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </div> <base target="_self" href="https://e.mail.ru/"> </div> </div> </div> </blockquote> -- Roman Klochkov </BODY></HTML>