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
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