#lang scribble/manual @(require scribble/eval (for-label racket sugar)) @(define my-eval (make-base-eval)) @(my-eval `(require sugar racket/list)) @title{List} @defmodule[sugar/list] @defproc[ (trimf [lst list?] [pred procedure?]) list?] Drop elements from each end of @racket[_lst] that satisfy @racket[_pred]. Exactly equivalent to @racket[(dropf-right (dropf _lst _pred) _pred)]. @examples[#:eval my-eval (trimf '(1 2 3 a b c 4 5 6) integer?) (trimf '(1 2 3 a b c) integer?) (trimf '(a b c) integer?) (trimf '(a b c 1 2 3 d e f) integer?)] @defproc[ (filter-split [lst list?] [pred procedure?]) (listof list?)] Like @racket[string-split], but for lists. Drop elements from anywhere in @racket[_lst] that satisfy @racket[_pred] — ends, middle, you name it — and return a list of the sublists that remain. @examples[#:eval my-eval (filter-split '(1 a b c 2 d e f 3) integer?) (filter-split '(1 a b c 2 d e f 3) (compose not integer?)) (filter-split '(a b c 1 2 3 d e f) integer?) (filter-split '(a b c 1 2 3 d e f) (compose not integer?))] @defproc[ (slice-at [lst list?] [len (and/c integer? positive?)] [force? boolean? #f]) (listof list?)] Divide @racket[_lst] into sublists of length @racket[_len]. If @racket[_lst] cannot be divided evenly by @racket[_len], the last sublist will be shorter. If this displeases you, set @racket[_force?] to @racket[#t] and a stumpy final sublist will be ignored. @examples[#:eval my-eval (slice-at (range 5) 1) (slice-at (range 5) 2) (slice-at (range 5) 2 #t) (slice-at (range 5) 3) (slice-at (range 5) 5) (slice-at (range 5) 5 #t) (slice-at (range 5) 100000) (slice-at (range 5) 100000 #t)] @defproc[ (slicef-at [lst list?] [pred procedure?] [force? boolean? #f]) (listof list?)] Divide @racket[_lst] into sublists starting with elements matching @racket[_pred]. The first element of the first sublist may not match @racket[_pred]. Or, if you really & truly want only the sublists starting with an element matching @racket[_pred], set @racket[_force?] to @racket[#t]. @examples[#:eval my-eval (slicef-at (range 5) even?) (slicef-at (range 5) odd?) (slicef-at (range 5) odd? #t)] @defproc[ (frequency-hash [lst list?]) hash?] Count the frequency of each element in @racket[_lst], and return a hash whose keys are the unique elements of @racket[_lst], and each value is the frequency of that element within @racket[_lst]. @examples[#:eval my-eval (frequency-hash '(a b b c c c)) (frequency-hash '(c b c a b c)) ] @defproc[ (members-unique? [container (or/c list? vector? string?)]) boolean?] Return @racket[#t] if every element in @racket[_container] is unique, otherwise @racket[#f]. @examples[#:eval my-eval (members-unique? '(a b c d e f)) (members-unique? '(a b c d e f a)) ] @defproc[ (members-unique?/error [container (or/c list? vector? string?)]) boolean?] Same as @racket[members-unique?], but if the members are not unique, raises a descriptive error rather than returning @racket[#f]. @examples[#:eval my-eval (members-unique?/error '(a b c d e f)) (members-unique?/error '(a b c d e f a)) (members-unique?/error '(a b c d e f a b)) ] @defform[(when/splice test expr)] A special version of @racket[when] that you can use inside @racket[quasiquote] to suppress @racket[void] values when @racket[_test] is @racket[#f]. As the name suggests, it works in conjunction with the @litchar["@"] splicing operator. @examples[#:eval my-eval `(,(when (even? 2) "hooray")) `(,(when (even? 3) "hooray")) `(,@(when/splice (even? 2) "hooray")) `(,@(when/splice (even? 3) "hooray")) ] @defform[(values->list values)] Convert @racket[_values] to a simple list. @examples[#:eval my-eval (split-at '(a b c d e f) 3) (values->list (split-at '(a b c d e f) 3)) ] @defproc[ (sublist [lst list?] [start-idx (and/c integer? (not/c negative?))] [end-idx (and/c integer? (not/c negative?))]) list?] Return a sublist of the @racket[_lst] starting with item @racket[_start-idx] and ending one item @bold{before} item @racket[_end-idx]. (Similar to how list slices are denominated in Python.) Thus the maximum value for @racket[_end-idx] is @racketfont{(length @racket[_lst])}. Errors will be triggered by nonsensical values for @racket[_end-idx]. @examples[#:eval my-eval (sublist '(0 1 2 3 4 5 6 7 8) 0 8) (sublist '(0 1 2 3 4 5 6 7 8) 8 9) (sublist '(0 1 2 3 4 5 6 7 8) 2 5) (sublist '(0 1 2 3 4 5 6 7 8) 5 2) (sublist '(0 1 2 3 4 5 6 7 8) 2 10) ] @defproc[ (break-at [lst list?] [indexes (or/c integer? (listof? integer?))]) (listof list?)] Break @racket[_lst] into smaller lists at the index positions in @racket[_indexes]. If a single integer value is given for @racket[_indexes], it's treated as a one-element list. Errors will arise if a breakpoint index exceeds the length of the list, or if the breakpoints are not increasing. @examples[#:eval my-eval (break-at '(0 1 2 3 4 5 6 7 8) 3) (break-at '(0 1 2 3 4 5 6 7 8) '(3)) (break-at '(0 1 2 3 4 5 6 7 8) '(3 6)) (break-at '(0 1 2 3 4 5 6 7 8) '(3 6 8)) (break-at '(0 1 2 3 4 5 6 7 8) '(3 6 8 10)) ]