NAME
====

OEIS - Look up sequences on the On-Line Encyclopedia of Integer Sequences®

SYNOPSIS
========

    use OEIS;

    say OEIS::lookup 1, 1, * + * ... *;
    #= OEIS A000045 «Fibonacci numbers: F(n) = F(n-1) + F(n-2) with F(0) = 0 and F(1) = 1.»

    say OEIS::lookup((1, 1, *+* ... *), :all).grep(* !~~ OEIS::easy).head;
    #= OEIS A290689 «Number of transitive rooted trees with n nodes.»

    say OEIS::lookup(1, 2, 4 ... ∞).mathematica.head;
    #= Table[2^n, {n, 0, 50}]

DESCRIPTION
===========

This module provides an interface to the [On-Line Encyclopedia of Integer Sequences® (OEIS®)](https://oeis.org), a web database of integer sequences. Stick an array or Seq into the `OEIS::lookup` routine and get back the most relevant result that OEIS finds, as an instance of [OEIS::Entry](OEIS::Entry). With the `:all` adverb, it returns a lazy Seq of all results. Sequences can also be looked up by their IDs. See below for details.

sub fetch
---------

    multi fetch (Int $ID, :$type 'A')
    multi fetch (Str $ID where { … })
    multi fetch (Seq $seq)
    multi fetch (*@partial-seq)

Searches for a sequence identified

  * its `Int $ID` under the `$type` namespace,

  * its `Str $ID` already containing the `$type`,

  * a Seq generating the sequence,

  * an array containing sequence elements

and returns all result pages in OEIS's internal text format as a lazy Seq.

This is a very low-level method. See [OEIS::lookup](OEIS::lookup) for a more convenient interface.

sub chop-records
----------------

    multi chop-records (Seq \pages)
    multi chop-records (Str $page)

Takes a single page in OEIS' internal format, or a Seq of them (the return value of [OEIS::fetch](OEIS::fetch)), and returns a Seq of all OEIS records contained in them, as multiline strings.

You will only need this sub if you get pages from a source that isn't [OEIS::fetch](OEIS::fetch), e.g. from a cache on disk, or if you want the textual records instead of [OEIS::Entry](OEIS::Entry) objects.

More a more convenient interface, see [OEIS::lookup](OEIS::lookup).

sub lookup
----------

    sub lookup (:$all = False, |c)

This high-level sub calls [OEIS::fetch](OEIS::fetch) with the captured arguments `|c`, followed by [OEIS::chop-records](OEIS::chop-records) and then creates for each record an [OEIS::Entry](OEIS::Entry) object. Naturally, all search features of [OEIS::fetch](OEIS::fetch) are supported.

By default only the first record is returned. This is the one that OEIS deems most relevant to the search. If the named argument `$all` is True, all records are returned as a lazy Seq.

If no result was found, the Seq is empty. Note that a too general query leads to "too many results, please narrow search" error from the OEIS. For other possible errors, see [X::OEIS](X::OEIS).

SEE ALSO
========

- [OEIS Internal Format documentation](https://oeis.org/eishelp1.html)

AUTHOR
======

Tobias Boege <tobs@taboege.de>

COPYRIGHT AND LICENSE
=====================

Copyright 2018/9 Tobias Boege

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.