#!/usr/bin/env perl
# Copyright (c) 2015-2020 Christian Jaeger, copying@christianjaeger.ch
# This is free software. See the file COPYING.md that came bundled
# with this file.
use strict;
use warnings;
use warnings FATAL => 'uninitialized';
use experimental "signatures";
# find modules from functional-perl working directory (not installed)
use Cwd 'abs_path';
our ($mydir, $myname);
BEGIN {
    my $location = (-l $0) ? abs_path($0) : $0;
    $location =~ /(.*?)([^\/]+?)_?\z/s or die "?";
    ($mydir, $myname) = ($1, $2);
}
use lib "$mydir/../lib";
sub usage {
    print "usage: $myname outpath numrows
  Write some useless number series in CSV format.
  Purpose: example and test for lazy list (streaming) code (check for
  leaks/memory retention).
";
    exit(@_ ? 1 : 0);
}
use Getopt::Long;
our $verbose = 0;
GetOptions("verbose" => \$verbose, "help" => sub {usage},) or exit 1;
usage unless @ARGV == 2;
our ($path, $numrows) = @ARGV;
use FP::Text::CSV qw(rows_to_csv_file);
use FP::List ":all";
use FP::Lazy ":all";
use FP::Stream ":all";
use FP::Ops qw(add);
use FP::fix;
use FP::Currying;
sub fibs () {
    # (Also see the [[fibs]] example script; unlike there, where
    # global scope is used, here we don't use Keep around $fibs as
    # it's correct when the local variable, which goes out of scope,
    # is deleted)
    my $fibs;
    $fibs = cons 1, cons 1, lazy { $fibs->stream_zip_with(\&add, rest $fibs) };
    $fibs
}
#sub exps($base, $start)
sub exps;
*exps = uncurry fun($base) {
    fix sub ($rec, $x) {
        lazy { cons $x, &$rec($x * $base) }
    }
};
sub series () {
    my $a    = 1.01;
    my $b    = 0.99;
    my $ns   = rest stream_iota;
    my $as   = exps $a, $a;
    my $bs   = exps $b, $b;
    my $fibs = fibs;
    (["n", "$a^n", "$b^n", "fib"], stream_zip $ns, $as, $bs, $fibs)
}
sub page ($title, $rows) {
    cons $title, $rows->take($numrows)
}
# Because of an unresolved issue (apparently in the Perl interpreter),
# the resulting stream has to be assigned to a lexical variable first,
# or the stream head would be held on to and the process would run out
# of memory:
my $page = page(series);
rows_to_csv_file $page, $path, +{ eol => "\n", sep_char => ";" };