List comprehensions are popularized by other functional languages like Standard ML, Miranda, Haskell.
Here, it is implemented with the macro collect, which is inspired by Clojure's for macro.
Other list-generating procedures, like range, repeat, iterate-times, iterate-until and iterate-while are provided as well, in a curried and an uncurried version. In the sequel, only the uncurried version is documented, the curried version is supplied to be used with map and friends.
- list-comprehensions sym ..procedure
Documentation procedure. Without argument, returns the list of exported symbols, with argument the documentation of that symbol.
- range uptoprocedure
- range from uptoprocedure
- range from upto stepprocedure
creates a list of numbers with given limits from defaults to 0 step defaults to 1
- iterate-times fn kprocedure
- iterate-times fn k startprocedure
produces a list where the items are constructed by successively applying fn k times to the last value, starting with start.
- iterate-while fn ok?procedure
- iterate-while fn ok? startprocedure
produces a list where the items are constructed by successively applying fn to the last value, starting with start, as long as the value passes the ok? test.
- iterate-until fn ok?procedure
- iterate-until fn ok? startprocedure
produces a list where the items are constructed by successively applying fn to the last value, starting with start, until the value passes the ok? test.
- (collect item qualifier ....)syntax
where item is an expression with variables to be bound in the qualifiers. Each qualifier is of the form (var lst fltr ...) whith
- var a variable
- lst a list from which values are chosen
- fltr a filter expression
Creates a new list by binding var to each element of lst in sequence, and if it passes the checks fltr ..., inserts the item expression into the result list. The qualifieres are processed sequentially from left to right, so that filters of a qualifier have access to the variables of qualifiers to its left.
(collect (list x y z) (x (list #\A #\B)) (y (list 1 2)) (z (list #f #t)))
((#\A 1 #f) (#\A 1 #t) (#\A 2 #f) (#\A 2 #t) (#\B 1 #f) (#\B 1 #t) (#\B 2 #f) (#\B 2 #t))
(import list-comprehensions) (range 0) ; -> '() (range 5) ; -> '(0 1 2 3 4) (range -5) ; -> '(0 -1 -2 -3 -4) (range 1 5) ; -> '(1 2 3 4) (range 5 1) ; -> '(5 4 3 2) (range 1 5 2) ; -> '(1 3) (repeat 5 'x) ; -> '(x x x x x) (iterate-times add1 5 1) ; -> '(1 2 3 4 5) (iterate-until sub1 zero? 5) ; -> '(5 4 3 2 1) (iterate-while sub1 positive? 5) ; -> '(5 4 3 2 1) (collect (list c k) (c (string->list "ABCDEFG")) (k '(1 2 3 4 5 6 7 8))) ; -> ((#\A 1) ... (#\A 8) ... (#\G 1) ... (#\G 8)) (collect (list c k) (c (string->list "ABCDEFG")) (k '(1 2 3 4 5 6 7 8) (memv c '(#\A #\G)) (memv k '(1 8)))) ; -> ((#\A 1) (#\A 8) (#\G 1) (#\G 8)) (collect (add1 x) (x '(0 1 2 3))) ; map ; -> '(1 2 3 4) (collect x (x '(0 1 2 3 4 5) (odd? x))) ; filter ; -> '(1 3 5)
Jul 05, 2019
Copyright (c) 2017-2019, Juergen Lorenz All rights reserved.
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- macro for renamed collect
- curried and uncurried versions, syntax of for changed
- initial import for chicken-5