avoid a list operation; fix error messages

dev-refac-2020
Matthew Butterick 7 years ago
parent b7933d769b
commit 803370572d

@ -139,7 +139,9 @@
(raise-argument-error 'sublist "list?" xs))
(cond
[(> j (length xs)) (error 'sublist (format "ending index ~a exceeds length of list" j))]
[(>= j i) (take (drop xs i) (- j i))]
[(>= j i) (for/list ([(x idx) (in-indexed xs)]
#:when (<= i idx (sub1 j)))
x)]
[else (error 'sublist (format "starting index ~a is larger than ending index ~a" i j))]))
@ -149,7 +151,8 @@
(raise-argument-error 'break-at "list?" xs))
(let ([bps (if (list? bps) bps (list bps))]) ; coerce bps to list
(when (ormap (λ (bp) (>= bp (length xs))) bps)
(error 'break-at (format "breakpoint in ~v is greater than or equal to input list length = ~a" bps (length xs))))
(raise-argument-error 'break-at
(format "breakpoints not greater than or equal to input list length = ~a" (length xs)) bps))
(when (not (increasing-nonnegative-list? bps))
(raise-argument-error 'break-at "increasing-nonnegative-list?" bps))
;; easier to do back to front, because then the list index for each item won't change during the recursion
@ -169,7 +172,10 @@
(modulo (abs how-far) (length xs))
(abs how-far)))
(cond
[(> abs-how-far (length xs)) (error caller "index ~a is too large for list of length ~a" (* (if (eq? caller 'shift-left) -1 1) how-far) (length xs))]
[(> abs-how-far (length xs))
(raise-argument-error caller
(format "index not larger than list length ~a" (length xs))
(* (if (eq? caller 'shift-left) -1 1) how-far))]
[(= how-far 0) xs]
[(positive? how-far)
(define-values (head tail) (split-at-right xs abs-how-far))
@ -212,8 +218,6 @@
(map (λ(how-far) (shift xs how-far fill-item cycle)) how-fars))
;; todo: can this work in typed context? couldn't figure out how to polymorphically `apply values`
;; macro doesn't work either
(define+provide+safe (shift/values xs shift-amount-or-amounts [fill-item #f] [cycle #f])
((list? (or/c integers? integer?)) (any/c boolean?) . ->* . any)
(apply values ((if (list? shift-amount-or-amounts)

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