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Various implementations of the @thi.ng/api
ISeq
interface / sequence abstraction and related tooling (inspired by
Clojure). Think of ISeqs as readonly sequential views & cursors of an
underlying (not necessarily sequential) collection...
Unlike with ES6 iterators,
ISeq.next()
is decoupled from an iteration step and merely produces a new view /
sequence head of the remaining sequence values. This allows forking &
sharing the sequence head(s) among multiple consumers, each able to read
the remaining values at their own pace.
ALPHA - bleeding edge / work-in-progress
Search or submit any issues for this package
yarn add @thi.ng/seqES module import:
<script type="module" src="https://cdn.skypack.dev/@thi.ng/seq"></script>For Node.js REPL:
const seq = await import("@thi.ng/seq");Package sizes (brotli'd, pre-treeshake): ESM: 533 bytes
import { aseq, rseq, concat, iterator } from "@thi.ng/seq";
// create a sequence abstraction of an array
const a = aseq([1,2,3]);
// aseq returns `undefined` for nullish or empty array arguments
// this is in accordance w/ the `ISeqable` interface
// see further below...
aseq([])
// undefined
// first() returns first value of seq (or undefined if empty)
a.first()
// 1
// next() returns new seq of remaining items
a.next()
// { first: [Function: first], next: [Function: next] }
a.next().first();
// 2
a.next().next().first();
// 3
// if the resulting sub-sequence is empty, next() returns undefined
a.next().next().next();
// undefined
// aseq() can take optional index range args
aseq([10, 20, 30, 40], 2).first()
// 30
aseq([10, 20, 30, 40], 2).next().first()
// 40
// the iterator here is only used for demo purposes
// (i.e. to convert the sequence to a standard ES6 iterable & show the result)
[...iterator(aseq([10, 20, 30, 40], 2))]
// [30, 40]
// rseq() produces a reverse sequence of the given array
rseq([1, 2, 3]).first()
// 3
rseq([1, 2, 3]).next().first()
// 2
// index ranges only (start MUST be > end)
[...iterator(rseq([0, 1, 2, 3, 4], 2))]
// [2, 1, 0]
[...iterator(rseq([0, 1, 2, 3, 4], 3, 1))]
// [3, 2]
// values can be prepended via cons()
[...iterator(cons(42, aseq([1, 2, 3])))]
// [ 42, 1, 2, 3 ]
// create new (or single value) seqs
cons(42).first()
// 42
cons(42).next()
// undefined
// zero-copy concat (supporting nullable parts/sub-sequences)
[...iterator(concat(null, aseq([]), aseq([1, 2]), undefined, cons(3)))]
// [ 1, 2, 3 ]
// if only arrays are used as sources, can also use concatA()
[...iterator(concatA(null, [], [1, 2], undefined, [3]))]
// [ 1, 2, 3 ]Since the entire approach is interface based, sequences can be defined for any custom datatype (preferably via the ISeqable interface), for example here using @thi.ng/dcons:
import { dcons } from "@thi.ng/dcons";
// concat reversed array with doubly-linked list
[...iterator(concat(rseq([1, 2, 3]), dcons([4, 5, 6])))]
// [ 3, 2, 1, 4, 5, 6 ]Lazily instantiated (possibly infinite) sequences can be created via
lazyseq(). This function returns an ISeq which only realizes its
values when they're requested.
import { defmultiN } from "@thi.ng/defmulti";
// defmultiN only used here to define multiple arities for `fib`
const fib = defmultiN({
0: () => fib(0, 1),
2: (a, b) => lazyseq(() => {
console.log(`realize: ${a}`);
return cons(a, fib(b, a + b));
})
});
fib()
// { first: [Function: first], next: [Function: next] }
fib().first()
// realize: 0
// 0
fib().next().first()
// realize: 0
// realize: 1
// 1
fib().next().next().first()
// realize: 0
// realize: 1
// realize: 1
// 1
fib().next().next().next().first()
// realize: 0
// realize: 1
// realize: 1
// realize: 2
// 2
fib().next().next().next().next().first()
// realize: 0
// realize: 1
// realize: 1
// realize: 2
// realize: 3
// 3If this project contributes to an academic publication, please cite it as:
@misc{thing-seq,
title = "@thi.ng/seq",
author = "Karsten Schmidt",
note = "https://thi.ng/seq",
year = 2019
}© 2019 - 2024 Karsten Schmidt // Apache License 2.0